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# III-V Semiconductors - Science topic

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Any hints regarding other porous III-V semiconductors are also welcomed.
Pavlo Sai thank you for the answer.
Aparna Sathya Murthy thank you for the publications. Especially the first one seems to correspond to my question very well!
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Does exist any interaction between the silicon contained into a silicon doped semicondutor and the acetone used to clean the sample? I use the sonicator.
Is there any article related to silicone and acetone interaction?
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Hello,
I want to model an heterostructure device with the drift-diffusion model, for that I need a boundary conditions. At the heterostructure there is a junction barrier that dictates a thermionic emmition current injection boundary at the junction (J=A*T^2*exp(Phi-dPhi/vt)). Moreover, due to poor surface conditions there is a high surface recombination, which is modeled as Jn=qS(n(0)-np0).
*Phi and dPhi are the junction barrier and reduced junction barrier respectivally.
Does these boundary conditions (thermionic emmition and surface recombination) can be combiend together or they equivalent in some degree?
Thanks.
The following RG link is also very useful:
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If we have a diode with p-type (Germanium) and n-type ( Silicon), then what will be the formula to find the built in potential?
Dear Amit Das ,
There is a general formulation for the contact difference of potential between two any two semiconductors or even two materials. Such junctions are called heterojunctions.
The contact difference of potential phi= The work function difference of the two contacted materials. Assume that the work function of the two materials are phi1 and phi2, then phi= Ph1-ph1
The work function of a material is the difference between the vacuum level and the Fermi-level= Ev-Ef
Best wishes
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Can we learn things from the shape of the IV curve of a diode in order to examine issues and phenomena that exceeds from ideal behavior? Things like the slope of the reverse or forward bias, the knee point s-shape, etc.
What mechanisms, for example, tunneling, SRH, strain in heterojunctions, shunt paths, schottky contacts, too high series resistance, hot carrier effects, panch-throghs, traps, non ideal doping, etc. These are known effects but I'm not sure if and how they reflect in the IV curve or if there are other less known effects that I missing out.
Are there good reviews summarizing different issues and effects in the device (design, process, fabrication) and how they con reflect on the IV curve?
Most material I found talks about these effects but in the context of desired effects on different devices.
Where can I start the learning of issues in PN diodes, or semiconductor structures in general.
Any input on this matter will be highly appreciated.
Thanks
I treated some anomalous behavior of pn diodes either homo or heterojunction in the context of operation of the solar cells. I could at that time model and fully explain the S- curve of the illuminated solar cell characteristics.
I also could fully explain the large ideality factors in heterojunction diodes and solar cells: I covered this issue in two papers:
Dependence of dark current on zine concentration in Znx Cd1-x S/Zn Te hetero – junctions“M. Abdelnaby, A. Zekry
Solar Energy Materials and Solar Cells 29 (january)
Capacitance and conductance of Zn/sub x/Cd/sub 1-x/S/ZnTe heterojunctions
A Zekry, M Abdel-Naby, HF Ragaie, F El Akkad
IEEE transactions on electron devices 40 (2), 259-266
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What will be the future of solar cells? Perovskite solar cells? OR III-V Solar cells ??
1. Perovskite solar : Easier to fabricate (can be printed like paper) and have low conversion efficiency but might include toxic materials.
2. III-V solar cell: Difficult to fabricate, however, it can provide higher efficiency (47.1%, 2020).
I think that the perovskite solar cells will be further developed to overcome its instability and toxicity. There is already appreciable advancements in the direction by using more stable perovskite materials and by using metal oxide transport layers which seal the material against the water moisture in the environments.
Because of the many advantages of such cell type it will be further developed for committal applications.
As for the the iii-v solar cells they may be used with optical concentrators.
But their cooling may limit their wide use in addition to the limited resources of their materials.
I am very convinced that the solar cell industry will be further depend on silicon solar cells with all type of silicon solar cells from the crystalline to the multicrysatlline to polycrystalline to microcrystalline to amorphous solar cells.
We developed newly the heavily doped silicon solar cells that do not need silicon with high purity or just need what is called solar grade silicon.
I would like that you follow our research by looking for example to the paper in the paper in the link:
Best wishes
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Group-IV elements doping in III-V behaves amphoteric: n-type if the dopants occupy the group-III sites and p-type if they occupy the group-V sites, which is not hard to understand.
My question is on a group-VI elements doping in III-V semiconductors. An example is Te doping in GaAs. Te atoms are known to occupy As sites and make GaAs n-type. When we excessively dope Te in GaAs, however, we observed that GaAs became p-type. I would guess that it happens as Te starts occupying Ga sites or interstitial sites.
First, has any of you observed this (p-type conductance from group-VI doping in III-V)?
Second, can anyone help me understand the mechanism?
The following articles might be useful
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I was trying to understand Lattice deformation and stress in epitaxial layers, when comes to the inclination angle △φ (lots of articles just give the equation...), it confused me a lot. I totaly have no idea how to get it.
Hello,
However, it seems that you are trying to compute the uncertainty in the inclination angle, where the measured variables are a (perpendicularly) and a (parallel). If you know the measurement uncertainties in these two quantities (e.g instrument error or uncertainty) then simply take the ratio as in the given equation. Eq. 13 refers to an absolute angle (phi) that should be known. I hope that helps.
Regards,
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Hello, everyone,
I'm a little confused about valence band structure of Aluminum nitride (AlN). It is known that the crystal-field split energy in AlN is negative, so there are a lot of papers saying that the crystal-field split-off hole band is the topmost.
On the other hand, according to the k.p method (for example, or ) valence band energies at k=0 can be expressed as shown in the picture below (where Δ1 is the crystal-field splitting).
For Δ1>0 (like in GaN or InN), E1>E2>E3 and the bands are usually reffered as HH, LH and CH, respectively, so the topmost band is the heavy-hole band.
For any values of Δ1 and Δ2, E2 is always larger than E3, so in the case of AlN E2>E1>E3 which should mean that the topmost valence band is the light-hole band. Am I missing something obvious?
Another quick question is about an appropriate interpolation scheme for hole effective masses of ternary alloys. Should we use linearly interpolated Luttinger-like parameters A1...A4 for a certain composition to calculate the effective masses (including strain effect if needed) or should we calculate effective masses for the binaries from their parameters A1...A4 first and then interpolate between the obtained effective masses?
The valence band ordering for the AlGaN alloys is discussed in
M. Feneberg et.al.
"Anisotropic optical properties of semipolar AlGaN layers grown on m-plane sapphire", May 2015
• Applied Physics Letters 106(18):182102 (year 2015)
• DOI:10.1063/1.4920985 (or full text in research gate)
The properties of AlN are discussed here:
M. Feneberg et.al.
"Anisotropic absorption and emission of bulk ( 1 1 ¯ 00 ) AlN"
• Physical Review B 87(23), 235209 (2013)
• DOI: 10.1103/PhysRevB.87.235209 (or full text in research gate)
Ruediger
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I am doing some FIB cuts and analyzing my layer stack. I always see dots in the InP and InGaAsP layers, but I don't know their origin. These dots do not appear when I do a SEM of a cleaved sample, so I assume the origin is related with the Ion beam process. I attached a picture of a SEM image after an FIB to make clear which dots I am referring to. Any help or reference to solve this question is highly appreciated!
I am looking to synthesize InP or InGaAsP colloidal solution, Could you help me?
Thanks.....
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How can the deposition time affect the carrier density concentration (electrodeposited thin film)
The deposition time affects the thickness and the homogeneity of the deposited film. The deposited film will be polycrystalline. Inside the grains the carrier concentration is more or less equals to that of the bulk material. Only the grain boundaries which makes the great effect on the mobility of the material rather than its carrier concentration. The carrier concentration is affected very slightly
by the film thickness except some trapping at the surface of the grains.
Best wishes
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The punch through mechanism is described as reverse bias applied to drain, which results into extended depletion region. The two depletion regions of drain and source therefore are intersectioned with each other, and this results into "one" depletion region, and flow of leakage current and consequently breakdown of MOSFET.
My question (by looking at the attached figure) is that how intersection of two depletion regions with electric fields in opposite directions (Eleft and Eright) can results in "one" depletion region. I believe opposite electric field cancel each other out and create a flat band region wherever the two depletion region coincide.
More explanation on punch through:
Cheers,
Amir
Dear Pranjal,
welcome,
To avoid punch through you have to increase the doping of the channel. But this would decrease the mobility of charge carriers . A common solution is to use the low doped drain where the space charge extends towards the drain rather than the channel.
Best wishes
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I am ICP etching AlGaAs Bragg structures using Ar, Cl2 and BCl3.
After etching (typically a few microns), there is material deposited on the surface and sidewalls of my photonic structures. I assume it is something like AlCl3... but I'm not sure.
I want to remove this deposited material as it increases the roughness.
I have tried H2O2, up to ~20% concentration, but this does not seem to help.
Does anyone know what the deposited material is, and how could I dissolve it away?
Vapour pressure of Aluminium Chloride 133.3 Pa (99 °C) 13.3 kPa (151 °C)
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I made a cut 60 degree to the primary flat {0-11) and made a sample of 4X8 mm with primary flat as the base. The shape of the sample is a parallelogram and I made scratch parallel to the primary flat (for the initiation of cleave), clamped it in a special sample holder for X-STM analysis and then tried to cleave it inside the STM chamber in UHV.
The cleave isn't atomically flat (110) but it has a lot of step edges as shown in the figure. I tried to cleave around 15 samples. Most of them look exactly the same way.
Any suggestions or ideas to cleave it properly are welcome.
Mattias Hammar Thanks for the suggestion. I always cleave only after cooling with LN2. Thinning down further is my next option to try.
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Hi there,
I'm looking to buy various photodiodes/solar cells for some experiments.
The cells I'm looking for are InGaP, CZAS (and CZT) and amorphous silicon.
Any pointers to where I could buy those type of cells? The higher the efficiency of the cells, the better but not the most important factor.
J
Naceur Selmane Thank you, that's amazing! I'll check it out!
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I know that Rashba coupling parameter magnitude in experiments is about 0.1 eV.A. I also have seen some papers that has reported gigantic Rashba couplings about 0.3 eV.A or higher magnitudes. If fact, I need to know that can we have small quantum rings (radius 20-60 nm) with about 0.2 eV.A or higher Rashba coupling?
Pedro L. Contreras E. you are welcome Prof. Contreras.
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Hi everybody,
I am preparing the presentation for my phd thesis and I would like to add some really concrete motivations to the introduction slides. My thesis focuses on the 3D-growth of III-V semiconductors monolithically grown on silicon. In the first part of my talk I should introduce the defects due to the monolithic growth of III-V on silicon and the different strategies used to filter these defects.
Therefore, I was thinking of starting with a slide of main motivation which will let the audience understand the following problem: defects affect the cost in semiconductors devices, therefore manufacturing companies are wasting money due to this. If we solve this problem we could potentially save this amount of money. However, I want to be more clear than that and give them some actual numbers. How much do defects cost for manufacturing companies ?
Of course, it would be amazing if you could point out some market analysis (qualitative and quantitative analysis), survey papers, etc. Thanks for your help. Ida LUCCI
Dear Ida Lucci,
Geetak's document addresses the so called manufacturing yield due to wafers' size, die size, and defective dies distribution function (that is a manufacturing parameters initiated defect distribution model on a wafer). It is not exactly what you looking for, as you want to show a single die yield improvement by such process steps that reduce the density of defects on a die by changing process and / or A3B5 components parameters. In other words, wafer statistics are not your key interest at first, until you understand what are the key mechanisms that reduce defects on a single die. If you know the answer, all you need to do is to assess the cost increase or decrease that is related to the defects reduction and then to see, if the overall manufactured dies cost sustainable or not with the positive effect of each particular device functionality improvement (as far as say reliability, parameters of operation improvement, etc.)
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I know that in order to alter the non-linear properties of materials like glasses, poling is used. My question is, is there any way to achieve that in GaAs? Thank you!
Large enhancement of conversion efficiency, for both second and third harmonic generation, is predicted when a TE-polarized pump field excites the guided mode resonances of the grating. At the onset of these modes the spectrum near the pump wavelength shows abrupt changes of linear transmission and reflection that follow a typical shape. Under these circumstances, the grating provides dramatic enhancement of local fields and fosters favorable conditions for harmonic generation processes, even in regimes of strong linear absorption at the harmonic wavelengths. In GaAs, second and third harmonic conversion efficiencies can be enhanced by several orders of magnitude larger than conversion rates achievable in either bulk or low-scale structures made of the same material. These efficiencies are not influenced by linear absorption, and they are unrelated to grating thickness.
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We consider purchasing a new notching/scribing tool. The major intended applications using such piece of equipment are as follows:
• Cleaving GaAs/InP/GaSb/InAs laser diodes for smooth facets
• Dicing laser bars
• Photonic Integrated Circuits (PICs) singulation
• Limited-Production Dicing
I wanted to check if any of you have any recommendations for a particular piece of equipment from any vendors (except Loomis), which can do these tasks very reliably. I prefer an automated system rather than a manual one.
Brian Thibeault just saw this neat gadget at a conference:
The wafer goes face-down, so it scribes on the back, and scribes all the way across the device. Manual, and possibly good for your lab's needs.
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I am trying to measure the I-V characteristic of a Schottky diode (ZnO on ITO) using a standard IV measurement machine. The sample was illuminated using SoLux lamp. The value of FF that it gives, is negative...It definitely does not sound right (considering FF=Vmp*Imp/Voc*Isc). Also, why the efficiency is infinity?
Does anyone have an explanation?
P.S: Results as shown below:
-8490155.3 Fill Factor [%]
2.947E+2 Pmax [mW]
-1.593E+0 Vmax [V]
-1.850E+2 Imax [mA]
-9.59E+0 LIV Rshunt [ohm]
-9.58E+0 Voc slope [ohm]
Inf Efficiency [%]
TIA
Dear Amir,
I know that i cam late to your question.
Dear Amir, it is clear that the sign of the current and voltage of the cell. You measure the characteristics of the cell in the fourth quadrant where the voltage is positive and the current is negative. In calculating the fill factor it is Pmax/ Voc Isc which is called also the curve factor so, it has a positive sign.
Th large fill factor value, means wrong calculations of Pmax as i see you voltage and current values okay.
Best wishes
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Hello,
I have been working on Au/n-GaAs (Si doped) Schottky junctions. It is very well know that dark reverse saturation current (J0) is primarily dependent on temperature and nothing else (in ideal case I assume!).
However, I can clearly see a doping concentration dependence on my experimental results, which I cannot figure out. It is observed that J0 is usually 100-1000 times smaller for doping concentration of 10^16 cm-3 than 10^17 cm-3.
Can anyone explain this?
Thanks,
Amir
Dear Amirhossein,
welcome,
I would like to add to Abu Kowsar that the dependence of the dark reverse situation current of your device on the doping concentration points out that barrier height at the interface is affected by the presence of surface state at the interface at the surface of semiconductor, here GaAS.
In case that the barrier height is dominated by the surface states such that there is Fermi level pinning at the surface, then the barrier height phi from the metal to the semiconductor can be expressed by:
phi = Eg- phi0 , where Eg is the energy gap and pho is the level of the surface state which is pinned to Fermi level. For lower doping concentration , phi0 will be lower and the barrier height increases leading to larger barrier height and consequently much smaller reverse current. This may explain your observation.
For more details you may refer to S MSze, physics of semicondcutor.
Best wishes
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Hi
Currently I am working on growth of epitaxial ternary and Quaternary III-V semiconductor alloys.
For my research it is needed to know the exact alloy composition using RBS.
Tata Institute of Fundamental Research, Mumbai is also having RBS .
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I want to simulate a III-V solar cell for various temperature starting from 0 to 300 degree Celsius. Please any one may help me out by providing brief idea about it.
Dear Girija
regards
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Hi
i am am trying to etch down NI layer with thickness of 100nm on nGaAs substrate. I have read reference articles mainly the handbook of metal enchants and tried using following solutions:
H2SO4:H2O ..... different ratios from 3:1 to 4:3 to 1:50. However the Ni layer did not etch but the substrate started to be etched which is not desired.
HNO3:H2O 3:7 .... not etching Ni
HNO3:HCL .... etching both nGaAs and Ni
Afte observing that the Ni is not being etched, I believe there maybe NiO on top of Ni that needs to be etched away. However to remove NiO, there is need for HNO3 which is not very appropriate for using with nGaAs. Any recommendations for etching the Ni layer?
Thanks
Try HCl and heat a bit.
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Can the concept of the N-face or the Ga-face exist when the GaN film is not a single crystal anymore but a polycrystalline film? Can there be something like a net polarity in poly films?
Of course, you can not determine the polarity by XPS.
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Hello,
Could someone please point me to some reference data on the pemittivity of semi insulating GaAs in the THz region (1-4 THz). Chochol et. al have published some work on doped GaAs but I'm looking for semi insulating GaAs.
Thanks.
Chochol work here:
In the 0.1 to 4 THz range, semi-insulating GaAs is slightly dispersive. It has a refractive index of approximately n = 3.6 to 3.7 as measured using a THz-TDS. So, permittivity calculated as epsilon_r = n^2 would be approximately 13.
Please see the following paper for more details:
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Hi,
I have deposited 100nm Au on 5nm Au using e-beam evaporation and conventional photo-lithography techniques. I used ~5nm Ni as an adhesion layer for 100nm Au, so basically the structure is Au 5nm/Ni 5nm/Au 100nm.
The lift-off of the 100nm Au is extremely hard. I usually rest the sample in acetone for couple of hours so the lift-off is complete. However, in this case even after days, the lift-off is not complete and there are lots of unwanted pieces of Au on the surface. I try to use ultrasound (40kHz) as little as possible because it damages to the structures and removes the main metal layer as well. However, for these samples I apply ~10sec ultrasound, but after ultrasound the quality of the 100nm Au is bad and so much of metal is gone.
Worth mentioning that I dip the samples in HCL (37%) for ~3sec and H2O for 5sec before the 100nm Au deposition to remove any unwanted organic particles on the surface.
Is there any solution to improve the deposition/lift-off process, so the final 100nm Au has a good quality and shape?
Amir
one of my feature size is 3.5 microns. For this I needed 20 min sonication in acetone. Then ok. But the expired photoresist could be an issue. For lifting off of those small features we use a process called image reversal with AZ5214E. It is image resersal so positive resist but it behaves like a nagative one giving you nagative profile for easy lifting off
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I have fabricated a Schottky junction (100nm Au on nGaAs substrate with Ohmic contact of AuGe(100nm)/Ni(30nm)/Au(50nm) on nGaAs) using ebeam evaporation...When I perform I-V measurements, there has been times where a current range of 500mA (or sometimes even lower) passes through the device and after that there is black hole (dot) on the surface of Schottky layer (where probe was touching). The device I-V characteristics becomes linear (previously it was a nice diode-like curve) and to me it seems like device is failing. What can be done to increase the tolerance of the device to withstand higher currents?
Hello Amir.
According to your description, after applying a rather large current, the Schottky junction at the Au/semiconductor interface is destroyed and the contact becomes an ohmic one.
Did you estimate the power dissipated in the junction (U times I) when the biasing current is reaching 500 mA? I don't know the lateral dimension of tour device, but the associated temperature increase is certainly rather high.
GaAs can easily react with gold even in the solid-phase: Ga atoms will diffuse into gold, destroying the stoechiometry of the GaAs material just below the interface. In the present case, the combination of heating and strong current degrades the interface and transforms the Schottky contact into an ohmic one. Sinc your gold layer is rather thin, the damage is localized in the tip area.
This is the reason why, in order to improve the robustness of Schottky diodes on GaAs, a first very thin (typ.50nm) titanium is first deposited (don't react with GaAs) followed by a very thin platinum layer (to avoid interdiffusion of Ti and Au), and then gold.
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Silicon nitride films (SiNx) can have a broad range of x-values (i.e., Si rich or N rich). Can similar be expected for GaNx?
Metal (Ga)- or N-rich growth exists in MBE or MOVPE. However, it does not change the GaN stoichiometry.
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Dear Experts,
Suggest me to mix two type of catalysts with one another, which in solid state form. I am also excepting with uniform perception.
How much weight are we talking about here, grams, kilograms? You could use a laboratory-scale end-over-end drum tumbler (with e.g. rubber stoppers put in the drum) which may help to thoroughly mix the two things.
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Hello everyone,
I have used Silicon and Magnesium as dopant materials for different layers of GaN photodiode. I have drawn the structure and used those dopant materials using Sentaurus TCAD. I was able to do meshing. I visualized doping profile in Meshing section.
After running simulation, I had the following issues:
No Species in doping file for incomplete ionization. !
Can someone please guide me how I can resolve the issue. I have not faced this kind of problem in Sentaurus TCAD while I was working on different types of Silicon photodiode devices with Boron and Phosphorus doping.
Thanks,
Mottaleb
Dear Nitish, Soumen Deb,
I have used "nSiliconActiveConcentration" in Simulating AlGaAs/GaAs  Hemt  with AlGaAs doping (5e17) I am getting e density nearly equal to doping Value
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In a research paper lattice parameters of GaN is
a=0.3232nm and c= 0.5269nm   c/a =1.630   B.G=1.596 eV
for InN
a=0.3628 nm and c=0.5870nm  c/a=1.618    B.G=0.001eV
But it is reported that lattice mismatch of GaN and InN is 10.0% for a and 9.3% for c.
how to find these lattice mismatch?
have any specific formula?
Thanks Hosni Saidi  & Rudolf Feile
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I am trying to use a small size crucible (smaller in volume) in ebeam evaporator for depositing expensive materials such as Au and AuGe. I also want the crucible to fit the pocket of the evaporator. Attached you can see the original size crucible that is being used and below that you can my design of smaller crucible. Smaller crucible is made by thickening the walls of the original size crucible (crucible material can be graphite copper or tungsten). However, the issue here is that the thick walls of the crucible may degrade the cooling process and result in crucible to break (crack).
What is the possible solution for having a smaller size crucible here?
I heard from a friend of using something like a "reducer" that I can fit inside the original size crucible and deposit my material. This reducer can be made of copper for example, which has good heat transfer.
I use a 7CC crucible when evaporating gold from either a 40CC pocket or a 20CC pocket... You do not need to have the crucible the same size... just make sure your beam is hitting directly in the middle of the pocket.  Additionally, for Au... why not just add a thermal source?  You dont need to put a shutter over it.  In my experience I was using about 6 grams of gold to get 150nm onto the substrate with the ebeam... I can use 1.5 grams of gold with a thermal source to get the same.  It is way more cost effective.  Additionally, you don't need to buy a fancy thermal power supply to do this.. I spent 800 bucks on a variac and a transformer and maybe 1000 bucks on the thermal feed thrus and everything works just fine :)
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Dear all,
I am not chemist and I can't really find the answer to my question in the litterature.
Could anybody suggest me a recipe for a non-selective wet etching of InGaAs and InP with similar etch rates? If possible I would like to avoid Brome based mixtures.
I was wondering if mixing in the same solution mixtures of H2SO4:H2O2:H2O (etching InGaAs) and HCl:H2O (etching InP) would do the trick. Any chemist could confirm?
Thanks a lot for your help.
Thibault
Actually this info is in review by Clawson [A.R. Clawson / Materials Science and Engineering 31 (2001) 1] on  p.17
HCl:HNO3 (1:2); equal etch rate on InP and InGaAsP 0:16 mm/s; Ref. (Furuya, K., 1981)
HBr:H3PO4:K2Cr2O7 (2:2:1); InP and InGaAsP equal etch rate 1:5 mm/min; does not attack photoresist; Ref. (Adachi, S., 1982a)
HBr:CH3COOH:K2Cr2O7 (1:1:1); InP and InGaAs mesa etch, equal rates for both; Ref. (Frei, M.R., 1991)
HBr:CH3COOH:K2Cr2O7 (2:2:1); nearly equal etch rate 2:5 mm/min for InGaAsP and InP.
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Hi everyone,
I want to dry etch III-N materials using BCl3 in a ICP-RIE system and I wonder if there are risks of samples or system contamination using this gas ?
As an addition of other researchers I would like ta add another point. If you use a mixed chemistry in your chamber you need to be careful. Especially Florine chemistry mixed with BCL3 may cause particle contamination if you mix (or sequential use) those process gases. You need to make proper cleaning and conditioning processes in between chemistry exchanges.
It would be better if you can keep the chamber walls at elevated temperatures if you use BCL3 because it may condansate or accumulate on the walls resulting corrosion, or you may use chamber liners to reduce system aging. I strongly reccomend to keep the turbo pumping all the time.
We have never experienced any contamination of a 3N material with BCL3. If you have questions in mind you may try very dilluted HF just after etching before mask strippimg. You may try 2 samples 1 with HF and 1 without HF and check the performance.
Besides the conramination, using just BCL3 in etching may not be suitable. You may need to mix BCL3 with Cl and maybe add some Ar to this mixture to obtain a reasonable eth rate, good surface quality and/or selectivity.
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I have read a fair few papers about this: defect models, papers that deal with demonstration of Fermi level depinning in Ge using certain top metal or MIS combinations. There is no doubt that the pinning position is near the valence band (VB) as I have confirmed this by experimentally measuring Schottky barriers for various metal/ Ge combinations (on both n and p type Ge).
Fermi level pinning is usually attributed to a distribution of donor and acceptor states near the VB forming a charge neutral level (~0.1 eV above the VB).
Unlike GaAs, I could not find any intuitive explanation for the physical origin of these defects (antisite defects seem to be the main candidates that behave like donor and acceptor states in III-V's). Moreover, segregation of group V atoms at atomic terraces are known to create dipoles that could affect the surface workfunction and local charge. Together, these phenomenon may somehow account for fermi level pinning. However, in Ge, there's only one species (Ge atoms) so I'm finding it hard to understand how both types of defects may arise. Are point defects (interstitials and vacancies) alone sufficient to create this effect? Could you provide any references that may be helpful? Thanks.
Srinivas,
The FLP at the surface of semiconductors due to the presence of high density surface states is an observed phenomenon. The complexity of this effect is that it depends on the surface properties of the material both chemically and geometrically. So, the findings may change from a laboratory to the other according to the surface treatment and the contacted environment. However there is studies of the germanium surface under well controlled conditions. Paul Handler and William M. Portnoy found that the surface of germanium has a strong p-type conductivity which is consistent with your observation of fermi level pinning at the surface near the valence band edge. They attributed this to : there is a two-dimensional surface state band at the surface which overlaps in energy a two-dimensional valence band just beneath the surface according to their expression in their paper at the link: http://journals.aps.org/pr/abstract/10.1103/PhysRev.116.516
I think this model can account for your experimental findings. An old paper but very useful.
Best wishes
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Why depletion region (i.e. built-in potential) in Schottky contact is smaller than the pn junction? In other words, why Voc of Schottky contact is smaller than the pn junction?
Does it have any relation with the types of charge carriers in these junction. I mean, since only electrons are the charge carriers in Schottky contact, therefore, the built-in potential is lower than the one in pn junction, where both electrons and holes are charge carriers and create stronger depletion region?
Dear Amirhossein,
Welcome,
The ideal value of the open circuit voltage is the contact difference of potential. The contact difference pf potential between two materials is difference between the work functions of the two materials, that is phi= phi1- phi2,
For the p-n junction assume phi1 is that of the p-type and phi2 is that of the n-type, then the highest possible difference is bounded by the energy gap. Because if the difference is increased beyond the energy gap the material will be metal ike and the barrier will be tunnel able. The practical value achieved for the open circuit voltage is about .6V  because one of the sides of the p-n junction must be moderately doped for effective collection of the generated electron hole pairs and  the real open circuit volatile condition is arrived when the photocurrent is equal to the dark current.
Then the open circuit voltage= nVt Ln ( Iph/ Is),
with n the ideality factor, Vt the thermal voltage. Iph the photo current and Is is the reverse saturation current of he junction.
In case of the Schottky diode solar cell and assuming n-type semiconductor, one can choose a metal such that its phi1 is equal to that of the p-type material. In this way the contact difference of potential is equal in both cases.
However the open circuit condition where the photocurrent is equal to the dark  current will result is a smaller open circuit voltage because the the dark current is a majority carrier current while in the p-n junction it is a minority carrier current.
The formula above for the open circuit holds also for the Schottky diode solar cell with the saturation current controlled by  potential barrier phib from the metal to the semiconductor. Phib= phi1- electron affinity of the semiconductor.Where phi1 is worfunction of the metal.
The presence of surface states at the semiconductor material may limit the potential barrier phib to about two thirds of the energy gap of the semiconductor.
There are some methods developed to increase the barrier hight by ion implanting the surface of the semiconductor to produce a heavily doped surface layer with doping type different from that of the substrate.
In summary,It is the nature of the flow of the dark current that make a difference in the open circuit volatile.
Best wishes
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In a Schottky solar cell, consider using an opaque metal on top of the bulk of semiconductor.
Depletion region exists mostly between the metal and semiconductor, and due to the opaque metal, therefore, solar illumination cannot  reach the depletion region. Therefore, no electron and hole are created in this region. However, electron and hole can be created in other areas in the bulk of semiconductor (outside of depletion region). Can these electron have any effect in creation of photogenerated current?
Dear Amirhossein,
welcome,
Your question is already answered in reference books of electronic devices. Please refer for example to the book physics and technology of electron devices by S.M.Sze. It contains a a description of operation of such MS soar cells.
It is so that the incident solar radiation will penetrate the material in the window regions between the metal stripes which are opaque as you said. The penetration depth depends on the wavelength of the incident radiation and the absorption coefficient of the material. Yes the shorter wave length radiation will be absorbed near he surface while the longer wavelength penetrates in the depth.
all of them generate e-h pairs causing an excess of electrons and holes in the material.
The electrons and holes generated inside the field region of the junction will be separated by this field such the electrons will be swept to the cathode while the holes will be swept to the anode. The electrons hole pairs generated out side the field region will diffuse to the field region because of the concentration gradient towards the field region. When they reach the drift region they will be separated similar to those generated inside the field region.
So, as you see the effect is exactly similar to the that occurring in the p-n junction.
The difference will be in the dark current. The current here is a majority carrier current with the injection over barrier limiting the dark current.
If you want to produce a field region over the whole surface and at the same time passing  light to the  active material you can either;
Cover the whole surface of the material with very thin metal layer,
or in case of silicon you can invert the surface region by just growing silicon oxide on it. The positive fixed charge at the oxide silicon interface can invert the p-substrate material into n-type, resulting in an induced n-p junction.
For more details see the reference given at the beginning of my comment.
wish you success
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I want to use RIE to etch GaN, I think I should use Cl2 and BCl3 but I need to know about the range of plasma power and working pressure.
I used Cl2 and Ar together. Here is the recipe:
chamber pressure ~ 20 mTorr
Power: 175 W
Cl2: 20 sccm
Ar:6 sccm
In order to etch 900 nm GaN/Al(6%)GaN, you need 8 min around. But you should etch for few min then wait for few min then etch for few min to avoid over heating. For 900 nm, 3 min etch and 2 min wait 3 min etch 2 min waiting then finally 2 min etch worked fine for me.
Also you should clean the chamber before you start etching for about an hour with this recipe:
Cl2/Ar   4/46 sccm  ,, 300 Watts, 60 min, 20 mTorr (or any value).
Then you should run a conditioning (same recipe as etching) for the time needed for actual etch. In our system it was difficult to control CL2 flow, so after conditioning I completely turned off the CL2 flow. Whatever left in the pipe line, it was enough to use for etching.
I hope this recipe work for you, too. You may need to optimize the values for your case.
Good luck.
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I would use them as the semiconducting llayer in transistor devices and as we dont produce them in our lab I need somewhere where i can purchase them.
Why is a glass substrate essential? As Esteban says the growth conditions required for high quality GaAs preclude it being down on glass.
What substrate properties do you need?
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Dear Experts.,
I got Cu doped SnO2 Nanoparticles with size (<25nm). Already i got good results in XPS compare to pure SnO2. In magnetisation also i got good ferromagnetic signals at variable temperatures (300 to 5 K). But i need to confirmed it mine is Dilute Magnetic Semiconductors or not ?
Pleased to give some supportive information with evidence.
Dear Raj Kumar,
you're writing you'having good results from both electron spectroscopy and magnetometry. Both types of experiments are non-trivial in terms of interpretation. So your statements evoke my curiosity and I wished I could see (some of) your data and interpretation and see whether I'd actually agree with you over this.
Whatever. In your case I assume that you think that Cu is the magnetic element. (Would be worth using experiments able to tell whether it actually is. There have been numerous erroneous assignments in the literature . ..) "dilute" then means that Cu is a foreign species in your host material and that compared to the density of unit cells its relative abundance is markedly smaller than unity. "dilute" and "magnetic" then refers to the situation that magnetic order is established despite the fact that the average distance between the magnetic sites is relatively large. So, if in your samples the Cu:Sn ratio is maybe of the order of just a few percent, then for me it would qualify as dilute.
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Increment of Metal loaded in semiconductor shows increasing bandgap with various composition.
There is another application for increasing the bandgap value that has been forgotten by the other pals: high temperature electronics, nice for motor cars and space (to explore planets closer to the sun) sensors and/or microprocessors. In the first part of the 90's, there were some groups that have studied this problem, seeking for applications of some materials such as diamond, silicon carbide and boron phosphide as well. The discovery of blue ray emission, carbon nanotubes, photovoltaics, and other nice problems have ecclipsed this subject matter.
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Normally, Bi are considered to replace V spices in III-V-Bi alloys.( For example, the most widely studied GaAs1-xBix). However, it might be not  the case in InPBi.  It is a crucial problem for our future studies.
Recently, we grow InPBi epitaxial  layers on InP(100) surface by gas source MBE and many novel  phenomena are observed. For example, the mid-infrared photoluminescence and new raman peaks at 150 and 170 cm-1  which remind us the Bin clusters (the new raman feature may also be expected when InBi bonds are formed. From the STM results, up to now, we were just able to see the P atoms of (110)  face where some of them are replace by Bi atoms ). I hope there are other methods to solve this problem. Welcome suggestions!
You can have InBi clasters, even as small as several atoms, in InP lattice. Small clusters should still be coherent with host lattice (but they may introduce strain to surrounding host lattice). So, not directly Bi_n clusters, when Bi is on both In and P sublattices, but (InBi)_n clusters, when Bi is still on P sublattice in InP, but locally aggregated into some larger molecules (several atoms) rather than nanoclusters (hundreds or thousands atoms). They may be hard to identify, as it is in case of high electrical doping.
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Dry etching methods for III-V photonic crystal slab layers are needed to complete our project.
Thanks very much!
Hi jiagen,
here at TU/e we have small but efficient nanophotonic foundry that is perfectly suitable for micro and nano-fabrication of custom photonics devices in III-V and Si like photonic crystals, gratings, waveguides, couplers, metasurfaces, plasmonics, nano-mems, ...
Price for Universities and Research Institution are pretty competitive :)
Let me know if we may be of any help with your project.
Kind regards
Francesco
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I am wondering if i have a GaAs solar cell and a Si solar cell, what would be the best combination to achieve the max power:
have a two modules  of series connected silicon (gaas) cells together, and then connect it to other module of series connected gaas (si) cell
or
connect one si cell to a gaas cell and then  make a module out of this combination?
Dear Amirhossein,
I agree filly with Tony, and add to him:
The rules of connecting solar cells in series that they have to have the same short circuit current.
The rules of connecting solar cells in parallel is that the solar cells must have the same open circuit voltage.
So, in your case since Ga As cells have higher open circuit voltage they could never be connected in parallel. They may be connected in series if their short circuit current is adjusted to be equal.
If this is not the case then one has  as Tony said, add then in the load after cascading every one with the proper DC to DC converter.
Best wishes
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I start work in the modeling material science. I doped GaN with RE and found that the impurities energy in the middle of Conduction band and valence band.
How to calculate the Band gap energy ? are we calculate like donor or acceptor ?
blue is conduction band and red is valence band, between that (the two line ) is maximum and minimum energy of impurities.
As long as one deals with a crystal with a translational symmetry of the crystal lattice one may apply the concept of band-structures 𝐸(𝒌).
Like for GaN. Its energy gap does not depend much on the concentration of impurities, as long as their concentration is small (e.g. 1012 -1018 cm-3 in comparison with ca.
1023 cm-3 Ga’s ).
But when the concentration of impurities increases and becomes comparable to the concentration of the lattice atoms, then one obtains e.g. (random) substitutional 𝐴x𝐵1-x alloys. They lack translational symmetry and thus the concept of a wave vector and a description by a band structure 𝐸(𝒌) becomes questionable. Different approaches have been developed (e.g. the virtual crystal approximation, coherent phase approximation, etc.) to deal with this subject by partially reestablishing the language of band theory.
For optimal electro- and photoluminescence an Er concentration in GaN is ~ 1 at% (Er in GaN:Er is found to replace Ga). Then the Er’s concentration has to be considered as high.
By describing the physical properties of disordered alloys via the spectral decomposition method by using supercells, one can still obtain an “effective band structure”. E.g., these calculations show for Inx Ga1-x that the energy gap decreases from 3.20 eV for GaN to 0.26 eV for InN and this alloy exhibits a well-defined “effective band structure”. Ga (N1-xPx), in contrast, shows a rapid disintegration of the valence band Bloch character and the appearance of a strongly localized level in the energy gap of GaN for vanishingly small amounts of P (e.g. x <0.004) in GaN. With increasing concentration of P (e.g. 𝑥≥0.01) this level evolves into an impurity band.
Among other methods this spectral decomposition method may be also appropriate for the determination of the energy gap and impurity levels or impurity bands for RE metals (e.g. Er) in GaN alloys in dependence on their RE concentration. Thus also in this direction one may have a look in the literature.
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Hi,
Which geometry of the metal contact on the semiconductor wafer can give best Schottky diode properties? Whether the circular metal dots or the large area of metal (say 1x1 cm2), which is deposited on the front surface of the wafer?
How does the performance depend on diode area?
Attached is just a rough sketch, what would be the best design?
I would say that the two geometries won't make much difference to the quality of the contact - this will be determined more by the surface and the materials properties. If you're concerned the metal won't make a good Ohmic contact with the semiconductor, I would suggest ensuring that the surface is free of passivating oxide and/or contaminants, and/or investigating which metals are best suited for making contacts on the semiconductor you're using.
Obviously the magnitude of the contact area will affect the absolute value of the current you measure - if the contact is properly Ohmic, then the resistance should be inversely proportional to the area. If the measured current is expected to be small, then the larger contact may be better to improve signal-to-noise ratio (depending on the sensitivity of your equipment). However, the dot pattern offers the advantage of being able to take multiple measurements on the same wafer and average the results, so I would recommend using the circular contacts unless their smaller size results in too small a current.
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As i just only understand that pinch off actually occur when apply some voltage on drain (VD) until equal to the drain voltage saturation (VDS) so that the depletion region at drain is increasing due to electrical field at the drain edge is decrease, thus only small electron and even no electron is induced at the drain edge. i just want to know Why actually it occur?
no channel exist at the drain end. but current flows due to the electric field in the depletion region. when electron comes to pinch off region, they all swept out to drain by the depletion region electric field. no of electrons reaching to drain is lesser but their average velocity increases. this results a constant current at saturation.
Long channel devices means when the channel length is long enough(~micro meter range). if your channel length is in nanometer range you will not get a constant current at saturation, drain current increases slightly with Vds. this is called short channel effect.
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Hi
I was wondering how carrier scattering varies with the defects in thin film semiconductors. For example if iii-V semiconductor grows on silicon substrate because of the lattice mismatch there will be lot of misfit dislocations and growth twins. Is there any straight forward answer where it can be said that the carrier scattering increases/decreases with line defects or stacking faults. Or if I pose the question like this: how the mobility  is affected by these defects. Will it increase or decrease by these defects? Or is it complicated to say? There exist lot of literature which mostly are misleading or I did not find very good answer in literature which can straight way gun down the question. Some literature says carrier scattering will be more with twin length some says it would decrease with coherent twin boundary length as twin boundaries are low scattering centers. I am not sure how to interpret. In my case I got twin formation between film and the substrate which drastically increases the conductivity. I am not sure whether to interpret that twin boundaries played a dominant role to reduce the carrier scattering and thus enhanced the mobility and conductivity or it has no effect on carrier mobility or scattering.  Your thoughts will be highly appreciable.
Ankurda,
Usually in nitride semiconductors heterojunctions there are various factors responsible for scattering mechanism,e.g.:acoustic phonon, optical phonon, ionized impurity, interface roughness, surface donor and most importantly threading dislocations. Under different ranges of temperatures one or other factor becomes more dominant than the other. In case of nitrides the dislocations are found to be more benign than other semiconductors. Generally , if the distance between two neighboring dislocations are longer than the scattering length of the electrons, no more further reduction of dislocations are of any help to enhance the mobility of the 2DEG formed at the heterojunction of AlGaN/GaN. Under that situation other factors need to taken care of.
Thanks
Abheek
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I want to reflow microposit S1813 photoresist around some 700-1000 um tall structures, so that the tips of these have almost no resist left on them. Any tips on how to do this?
Hi,  and thanks a lot Jules. What I am attempting is to cover some pyramidal microstructures covered in thin oxide, and then expose the tip for etching away the oxide and do metallization. It seems that 130 C in a convection oven for 30 minutes does the job with a pretty thin resist, close to what you suggested.
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I need reference spectra to compare with. I have measured the Aluminium-K absorption edge for an AlInP layer. If anyone knows literature data or has performed similar experiments please let me know.
Thanks
I have a Al foil and Al2O3 foil measured at K-edge (see attached file).
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Why we cannot crystallize III-V simiconductors out of solution (aqueous or organic solvent)? for example cannot obtain in VLS (vapor-liquid-solid) method and force to use SLS (solution-liquid-solid) method?
The challenge lies in poor solubility of these compounds. Nucleation is supposedly easy, but there is no growth and then no crystals of appreciable size are produced. Some attempts have been made by the group of Prof. Brock, please, see:
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We know that most of the 2DEG-electrons in the undoped AlGaN/GaN heterostructure comes from the surface donor states (UK Mishra et. al and Guang et. al.). These electrons are driven by the electric field due to two sheet charge at the AlGaN-surface (-ve) and the interface (+ve). Now, when the electrons from the surface donor states travel to from 2DEG, they have to go past the +ve sheet charge in the interface (AlGaN-side). Why don't the electrons recombine with the +ve sheet charge before getting confined into the GaN side of the heterostructure and forming 2DEG?
If you want to understand modern theory of polarization in more detail, see this reference (http://link.springer.com/chapter/10.1007/978-3-540-34591-6_2). It is pretty involved but I hope it helps clear up some concepts about bulk polarization vs polarization discontinuities.
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Usually III-V semiconductors have direct band gap and can be calculated directly by some mathematical manipulation, however few inorganic materials usually don't exhibit a prominent absorption band edge!!!.
How the band gape is estimated for such type of materials?
As Sobia Dilpazir told, Tauc plot is used to determine the optical gap, in semiconductors.
Tauc, J., Grigorovici, R., & Vancu, A. (1966). Optical Properties and Electronic Structure of Amorphous Germanium. Physica Status Solidi (b), 15(2), 627–637. doi:10.1002/pssb.19660150224
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III-V semiconductors have tetrahedral crystal structure with sp3 hybridization. Does all materials that have this type of crystal structure have semiconductor properties? Does this include organic compounds also?
Ranjith,
The elementary semiconductor materials like silicon are characterized by tetrahedral covalent bond, where every atom is bound to four neighboring atoms. Three five compounds behaves in the same manner forming zinc blende structure.
Accordingly the valence band will be filled with electrons and the conduction band will be empty at zero kelvin. At room temperature, the valence band will be partially empty and the conduction band will be partially filled resulting in conduction by holes in the valence band and electrons in the conduction band. By doping the material one can control the hole concentration and the electron concentration and this is one of the great properties of the semiconductors.
So, a semiconductor can be recognized by a chemical bond, a crystallographic  structure, and en energy band structure.
It is so that the semiconductors are classified into elementary and compound semiconductors. The compound semiconductors are clarified into three five compounds such as GaAs, and two six compounds like CdTe.
It is so depending on the value of the energy gap, these compounds can have metal like properties to semiconductors to semi insulators.Organic semiconductors under go such main properties. But it is noticed the organic semiconductors ha short range order rendering the conduction band very narrow with very high effective mass of electrons in such materials
Best wishes
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But other iii-v semiconductor do not have that much high band gap? What is the speciallity of GaN crystal which makes its band gap that high than any other semiconductor?Also how it consumes less power and the brightness/watt is more than any other light sources such as CFL which makes its use in LED possible?
The answer to this question is fundamentally impossible to give as the property in question is a result of the arrangement of the Gallium and Nitrogen atoms. It's the equivalent of asking "why is water clear?" It's a natural consequence of the atomic arrangement, which forms the molecular band structure of the material. Once you solve the appropriate equations for the atomic structure of GaN, you'll arrive at the appropriate, crystal direction-dependent, energy band diagram. Outside of the math, the answer to your question is a philosophical one rather than a scientific one.
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This is a vertical Tunnel FET fabrication
I need to fabricate In0.53Ga0.47As  and In0.7Ga0.3As layers for a vertical TFET
Dear Praveen C S,
Yes, you can use Atomic Layer Deposition (ALD) to grow InxGa1-xAs.
Some relevant papers are recommended.
Please note that Atomic Layer Epitaxy (ALE) is sometimes referred to ALD.
[1]  Incorporation of indium and gallium in atomic layer epitaxy of InGaAs on InP substrates [http://www.sciencedirect.com/science/article/pii/S0022024811002491]
[2]  Role of interface strain in atomic layer epitaxy growth kinetics of InxGa1−xAs [http://www.sciencedirect.com/science/article/pii/002202489190675U]
[3]  A comparative study of the growth mechanism of InAs/GaAs and GaP/GaAs heterostructures and strained layered superlattices by atomic layer epitaxy [http://www.sciencedirect.com/science/article/pii/S0022024804019190]
Good luck!
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Which case is shows more doped Metal (Cobalt) into semiconductor nano-TiO2.
1. Metal (0.02g) doped into semiconductor (0.1g).
2. Metal (0.02g) doped intoi semiconductor (0.3g)
What happens when we increase semiconductor ?
Dear RAJ,
Do you want to calculate the atomic percent in two cases?
The doping in case 1 i greater than that in case 2. The weight percent in case 1 is 20 percent and in case 2 is 2/30 = about 6.6 percent.
when you increase the semiconductor keeping the metal weight constant the doping decreases.
wish you success.
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For coating the ceramic AlN substrate with Au using e-beam evaporator,  what metal layer should be used at first as an adhesion-promoter? Is it Ti? In fact, I evaporated Ti/Au(20 nm/800 nm) on ceramic substrates, however, I experienced the metal peeling-off problem as shown in the attached file.
Could this problem be due to the fact that the substrate is not cleaned enough prior to loading it into the chamber? Is the pre-cleaning process very critical? How to clean the substrate before loading into the chamber?
I agree, cleaning should be the first thing. You can sonicate in acetone, then methanol and then isopropanol for a couple of minutes each time (as long as they don't react with the ceramic). Also you can try to put more Ti (it looks like you are depositing a lot of Au), a rule of thumb is 10:1 for Au:Ti. Also try a lower deposition rate (I think it will help too), maybe less than 1.0 A/s. A lower deposition rate will help for better vacuum and in general that is better, you can even evaporate in steps to allow the pressure keep low and don't let the material heat up too much. I particularly prefer Cr rather than Ti, it has better adhesion, but you need to consider that it is magnetic.
Good luck
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I have simulated a p-i-n photodiode in Si, which has a large intrinsic region width, to capture a broad range of wavelengths from 400 nm to 900 nm. I see that the spectral response peaks at about 625 nm. I am interested to know why this happens at this wavelength?
I would expect the curve to decrease from the lower to the higher wavelengths, due to decreasing absorption coefficient values. Or is there something that I am missing here? Thanks for any clue!
The various series of silicon pin photodiodes are optimized for certain range of wavelengths. The pin photodiodes optimized for wavelengths 450…950 nm has the peak quantum efficiency (> 95 %) at wavelength of 625 nm.
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In multi-junction PV cell assemblies, why is it common for the substrate to be a metallic-ceramic-metallic structure?
What purpose does each layer serve exactly?
You have to have electrically insulating material as a core substrate, it may be glass , plastic or ceramics such alumina. The alumina may have the best thermal conduction among the three materials. It is also strong and durable. The alumina here is in form of a foil with small thickness such that its thermal resistance is reduced. The alumina sheet and the underlying metal  layer forms a combined bi layer structure  to improve the mechanical and thermal properties of the substrate such as the ability of folding and rolling.
wish you success.
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I know the difference between GaAs(111)A and (111)B is the surface termination. Now I have GaAs(111)A wafers for epitaxy puropse, and since it is double-side polished, can I just use the backside as (111)B, or it is not epi-ready in terms of growth purpose? On the other hand, I found little suppliers for GaAs(111)B with ONE side polished; and two-side polished wafers just increase the complexity of my experiment. Is there a special reason about this?
Growth on (111) is very different from (11-1) as the latter has a low growth rate and the (111) a 100 times higher growth rate surface in GaAs, see L. Hollan and C. Shiller, J. Crystal Growth 13/14, 319 (1972) and W. Shaw, J. Electrochem. Soc. 115, 405 (1968). The reason is the stability of the different surface reconstructions on these orientations.
Hence there in practive is no stable (111) surface obtained. Because the higher growth rate results from a strong sticking and thus a very low mobility on (111). However, a (111) surface can be stable (thermodynamically) at low V/III ratios (i.e. a very low growth rates for near equilibrium and low arsenic pressure). See the calculated WUlff plot (from A. Kley at FHI-Berlin 1997) In practice this is almost impossible to achieve in MOVPE but maybe possible via MBE.
About double side substrates: As written above those are first polished on one side, then mounted (glued) on that polished side and the final surface CMP is done; this is also done using a much finer polishing paste. While both side may look shiny, one side is much flatter and has much less polishing damage than the other. For epitaxy one the backside (and generally for any GaAs growth) you could try to etch the surfaces. An epi-ready ozone treatment tend to fail on high-index GaAs surface. If you attempt growth with MOVPE, a long anneal in H2 and AsH3 at 650°C may help before growth.
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Is there any relation between traps energy level and electron capture cross-section in semiconductor materials? Where can I find the theory or experimental data related electron capture cross section for the trap assisted recombination for GaAs material? Any good book suggestion will be very useful.
There is no rigorous theory linking electron/hole capture cross-section with the trap energy. I am not aware of any rigorous theory for the cross-section of a trap for capture of electrons or holes. The capture cross-section represents the probability of the trap capturing the free carrier. It should depend upon the physical/chemical identity of the trap and more importantly upon the charge state of the trap. In general, it is believed that Coulombic attraction between the trap and the carrier increases capture cross-section, while Coulombic repulsion decreases the capture cross-section, by orders of magnitude. For a neutral trap, the capture cross-section is about 10E-14 to 10E-15 cm2, while in the case of Coulomb attraction, it may be as large as 10E-10, and for Coulomb repulsion, it may be as low as 10E-19 cm2.
Experimental data are meagre in the case of GaAs traps. The main problem is that there are very few reliable techniques for the determination of the capture cross-section of the trap. However, there is substantial data on silicon/silicon-dioxide interface traps, obtained from the MOS admittance technique. Some experimental results indicated the capture cross-section to decrease with the interface trap energy moving towards the band edges.
References:
1. EH Nicollian and JR Brews, MOS Physics and Technology, Wiley, 1982.
2. A. Rose, Concepts in Photoconductivity and Allied Problems, Wiley, 1963.
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We have super high resolution (76um Pixel, <2 Arc Sec) XRD rocking curve data for a 0.5um MBE Super Lattice (SL) epi of InAs/InAsSb on (001) GaSb 25nm period. We would like to map the estimated relative epitaxial film thickness from this data.
Raw real time data showing up to 4 harmonics from SL structure, (004) symmetric reflection XRD rocking curve analysis: https://www.youtube.com/watch?v=De_Nh7iN6y4&list=PL7032E2DAF1F3941F&index=29
Comparison of the substrate GaSb (004) with Theoretical and Experimental GaAs (004): https://www.flickr.com/photos/85210325@N04/10647827636/in/set-72157648319384526   Ideally, we should have compared with the data from the substrate GaSb prior to epi deposition, in situ perhaps!
Q1. Is it reasonable to assume that the diffracting volume across the X-ray topograph is constant for an "optically flat" sample using the parallel beam geometry/optics. As long as the collimated incident beam's wavelength (energy) dispersion is constant (unchanging), this would work. Even if the beam monochromation wasn't perfect (a delta function). Correct?
A1. Seems to be "YES" based on feed-back thus far 11-11-14.
Q2. As in this case, if the estimated penetration depth is in the order of 12-15um, the epitaxial film would then diminish the substrate reflection intensity based on its thickness. Therefore, the integrated intensity from the substrate below the epitaxial film would be inversely proportional to the epitaxial film thickness. However, the sensitivity of this signal (from substrate plus 0th order peak of epi) to the epi thickness is a lot lower than the direct signal from the epi alone as we can considered in the +2nd Order Reflection (960 Arc Sec on RHS of the GaSb substrate peak in figure below of the relative reciprocal space map, Y-Omega, for the SL sample). https://www.flickr.com/photos/85210325@N04/15527541937/
A2. "Jury is still out".
The key to precision in this case would be the correct identification and deconvolution of the "background signal" and the incident beam shape factor. Using an advanced 2D detector & image processing techniques, the SNR with a <2kW conventional laboratory source doesn't seem to be a challenge. Could always use more signal :-)
Appreciate the erudite and expert RG membership's help!
I hope I get the question correctly. Your SL peaks (important: their integrated intensity) are supporting points for the envelope function. This envelope function (for the theta-2theta scan) corresponds to the diffraction signal from your InAs/InAsSb bilayer (convolution theorem for Fourier Transforms). However to extract the relative film thicknesses the information may be difficult to extract from one Bragg peak only. The 200 in addition has better contrast between InAs and InAsSb. In any case the fit of such an envelope has to take into account strain and thickness of both layers. Strain gradients maybe neglected as pseudomorphic growth can be expected in your materials with (hopefully) no significant plastic relaxation effects
So SL peaks for two symmetric reflections would carry more information. If I understand correctly, your substrate peak falls exactly on one SL peak. In this case I see no way how this SL peak can be used for data analysis and it should thus be omitted. It is very important to take the integrated intensities as supporting points of the envelope as the peak intensities are affected by SL imperfections (as drifts etc..).
I have fitted SLs in this paper :
and as you can see in Fig3, I included all kind of imperfection parameters in the SL simulation in order to fit the real data with the only goal of extracting the relative thicknesses AND strains. The effort (writing a ab initio simulation for each superlattice) could have been significantly shortened would I have extracted only the integrated intensity of every SL peak and fitted the envelope.
Or here:
http://www.schuelli.com/ in PhD thesis pages 50-56 and 81-92.
again the effortwas disproportional and the key figure in the data is not to sample at very high resolution the SL (in this particular case maybe, as the SL was perfect) but to get integrated intensities of as many SL peaks as possible.
For your point 1): I would say yes, as your lateral beam size on the sample seems to be much larger than the SL thickness one can consider the illuminated volume to be constant.
Point 2) I hope this is explained above
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I am working on two types of MSM photodetector ,on of them ohmic the other one schottcky. I studied sensitivity of both detectors, I saw sensitivity decreasing at high voltage in range (5-10)v
The question is why did sensitivity decrease at high voltage(5-10)v of MSM photodetector?
sensitivity =photocurrent/dark current
Dear Sha,
I agree with Han interpretation. However let make some comments which may be useful for this issue:
- The sensitivity of the photo detector is normally defined by the ratio of the photocurrent  to the the power of the incident radiation.
- From the shape of the dark characteristics one can identify the the type of the MS contact, i. e. , whether it is rectifying or ohmic. If it is rectifying then it operates as a photdiode. When it is ohmic it will act as a photocoductor or a photoresistor.
- Photodiodes working in reverse bias have their photocurrent constant with the reverse voltage so long as they do not enter in breakdown region. Their dark current is  equal to the reverse saturation current which may increase with the reverse voltage.
- In case of a photoconductor  The photocurrent may increase linearly with the applied voltage while   the dark current may increase at low voltage linearly and then more than linear at higher voltage because of the heating effects as hinted by Han. So the ratio will be constant at low voltage where the heating effect is negligible and the decreases at high voltage because of the heating effect.
You can prove that by measuring the currents as a function of the voltage.
wish you success.
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