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ABSTRACT: This special issue addresses to a large extent the challenges and opportunities in GaN and ZnO devices and materials deemed critical to both the GaN- and ZnO-based technologies. There are twenty articles in this special issue.
Proceedings of the IEEE 08/2010; · 6.81 Impact Factor
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ABSTRACT: AlGaN/GaN double heterostructure high electron mobility transistors (DH-HEMT's) with a 2.0 μm gate length and a 4 μm channel length, exhibiting good temperature characteristics, have been demonstrated. The maximum drain current I<sub>ds</sub> and extrinsic transconductance G<sub>m</sub> are 1300 mA/mm 235 mS/mm, 85.0 mA/mm 174 mS/mm, and 475 mA/mm, 95 mS/mm, respectively at T = -194°C, 20°C and 400°C. The temperature coefficient of I<sub>ds</sub> and G<sub>m</sub> are -1.4 mA/°C and 0.24 mS/°C respectively.
Solid-State and Integrated Circuits Technology, 2004. Proceedings. 7th International Conference on; 11/2004
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04/2002;
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ABSTRACT: We report on the calculation of electrical characteristics of
AlGaN/GaN heterojunction field effect transistors (HFETs). The model is
based on the self-consistent solution of the Schrodinger and Poisson
equations coupled to a quasi-2D model for the current flow. Both single
and double heterojunction devices are analyzed for [0001] or [000-1]
growth directions. The onset of a parasitic p-channel for particular
growth directions and alloy concentrations is also shown
IEEE Transactions on Electron Devices 04/2001; · 2.32 Impact Factor
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ABSTRACT: We have determined the electronic properties of an organic PPV film deposited on a p+-doped GaAs substrate by scanning tunneling spectroscopy. The normalized dynamical conductance curves of the PPV chains show well-defined conduction onsets and/or slope changes corresponding to the electron conduction through the LUMO and HOMO levels under forward and reverse bias. A theoretical calculation of the electronic transmission coefficient is used to describe the tunneling current as a function of the sample bias and to understand the electronic properties of the polymer. From the comparison between the calculations and the experimental results we obtain the single particle energy gap, the Fermi level position and the charge-carrier type.
Phys. Rev. B. 01/2001; 63(7).
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ABSTRACT: We have performed a systematic investigation of GaN/AlGaN quantum wells grown on different buffer layers (either GaN or AlGaN) in order to clarify the role of strain, structural parameters, and built-in field in determining the well-width dependence of the ground level emission energy. We find that identical quantum wells grown on different buffer layers exhibit strong variation of the ground level energy but similar well-width dependence. The data are quantitatively explained by an analytic model based on the envelope function formalism which accounts for screening and built-in field, and by a full self-consistent tight binding model. © 2000 American Institute of Physics.
Journal of Applied Physics 02/2000; 87(5):2289-2292. · 2.17 Impact Factor
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ABSTRACT: We report an investigation of wurtzite GaN/AlN heterostructures grown on Si(111) substrates by MBE, based on scanning tunneling microscopy measurements in air and photoluminescence. The scanning tunneling microscopy analysis of the sample surfaces demonstrates that the morphology of the GaN layers depends strongly on the thickness of the thin AlN buffer layer and has a weaker dependence on the substrate temperature during growth. GaN layers grown directly on the Si substrate or on a thin (<10 nm) AlN buffer layer present surface defects that can be associated with the formation of screw dislocations with their axis parallel to the growth direction. The photoluminescence spectra show strong extrinsic emission lines for all the investigated samples.
physica status solidi (b) 11/1999; 216(1):701 - 706. · 1.32 Impact Factor
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ABSTRACT: Decay of the longitudinal-optical (LO) phonons in wurtzite GaN has been studied by subpicosecond time-resolved Raman spectroscopy. Our experimental results show that among the various possible decay channels, the LO phonons in wurtzite GaN decay primarily into a large wave-vector TO and a large wave-vector LA or TA phonon. These experimental results are consistent with the recent theoretical calculations of the phonon dispersion curves for wurtzite GaN. © 1998 American Institute of Physics.
Applied Physics Letters 04/1998; 72(17):2132-2134. · 3.84 Impact Factor
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G. Y. Xu,
A. Salvador,
W. Kim,
Z. Fan,
C. Lu,
H. Tang, H. Morkoc,
G. Smith,
M. Estes,
B. Goldenberg,
W. Yang,
S. Krishnankutty
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ABSTRACT: We have investigated the spectral response of front-surface-illuminated GaN and AlGaN/GaN p-i-n ultraviolet photodetectors prepared by reactive molecular beam epitaxy on sapphire substrates. GaN homojunction p-i-n photodiodes exhibited a peaked response near the band edge. This enhanced response was absent in the AlGaN/GaN heterojunction p-i-n detectors. We analyzed the effect of p -layer thickness of the GaN p-i-n diodes on the magnitude of the peak photoresponse. The AlGaN/GaN photodiodes had a maximum zero-bias responsivity of 0.12 A/W at 364 nm, which decreased by more than 3 orders of magnitude for wavelengths longer than 390 nm. A reverse bias of -10 V raised the responsivity to 0.15 A/W without any significant increase in noise. The root-mean-square noise current in a 1 Hz bandwidth is ∼1.0 pA, corresponding to a noise-equivalent-power of ∼8.3 pW. We measured extremely fast decay times of 12 ns for the AlGaN/GaN and 29 ns for the GaN photodiodes. © 1997 American Institute of Physics.
Applied Physics Letters 11/1997; · 3.84 Impact Factor
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ABSTRACT: Ti/Al/Ti/Au ohmic contacts with low contact resistance (as low as 0.24 Ω mm) were used in fabricating short gate length modulation-doped field effect transistors on MBE-grown AlGaN/GaN layers. Maximum drain current achieved was above 1 A/mm with a transconductance of 182 mS/mm. RF measurements showed a maximum f<sub>τ</sub> of 35.9 GHz and an f<sub>MAX</sub> of 57.0 GHz, both achieved with 0.15 μm gate length. Simple analysis showed an electron saturation velocity of 1.3×10<sup>7</sup> cm/s in our device structure. Maximum gate-drain breakdown voltages for these devices were measured to be 30 to 35 V
Compound Semiconductors, 1997 IEEE International Symposium on; 10/1997
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ABSTRACT: Ti/Al/Ti/Au ohmic contacts with low contact resistance (as low as
0.24 Ω mm) were used in fabricating short gate length
modulation-doped field effect transistors on MBE-grown AlGaN/GaN layers.
Maximum drain current achieved was above 1 A/mm with a transconductance
of 182 mS/mm. RF measurements showed a maximum f<sub>T</sub> of 35.9 GHz
and an f<sub>max</sub> of 57.0 GHz, both achieved with 0.15 μm gates.
Simple analysis showed an electron saturation velocity of 1.3×10
<sup>7</sup> cm/s in our device structure. Gate-drain breakdown voltages
for these devices were measured to be 30 to 35 V
High Speed Semiconductor Devices and Circuits, 1997. Proceedings., 1997 IEEE/Cornell Conference on Advanced Concepts in; 09/1997
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ABSTRACT: The high electron peak and saturation velocity and a large
breakdown field attributes of GaN combined with its good thermal
conductivity and stability make it a suitable material for electrical
devices intended for high power applications. The wide band gap of GaN
leads to low intrinsic carrier concentration enabling a more precise
control of free carrier concentration over a wide range of temperatures.
In this paper we present AIGaN/GaN double heterostructure channel MODFET
exhibiting record dc performance at room and elevated temperatures
Device Research Conference Digest, 1997. 5th; 07/1997
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G. Xu,
A. Salvador,
A. Bothckarev,
W. Kim,
Z. Fan,
H. Tang, H. Morkoc,
G. Smith,
M. Estes,
B. Goldenberg,
W. Yang,
S. Krishnankutty
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ABSTRACT: UV-sensitive, visible-blind photodetectors have potential
applications in solar astronomy, missile plume detection, and combustion
monitoring. In these applications, one would like to detect the
intrinsic UV emission in a background of intense visible radiation. A
leading candidate for these tasks is a GaN-based photodetector. To date,
the majority of the effort in exploiting this material system for UV
detection has concentrated on GaN-based photoconductors which suffer
from long decay times and dark current. GaN p-n junction detectors and
Schottky junction detectors have also been reported recently. For high
speed and low noise applications, p-i-n photodetectors are generally
more desirable as they lack the negative attributes of photoconductors.
In this letter, we report on the performance of GaN p-i-n photodetectors
grown by reactive molecular beam epitaxy with ammonia as the nitrogen
source
Device Research Conference Digest, 1997. 5th; 07/1997
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ABSTRACT: A continuous wave output power of 1.5 W/mm with a power added efficiency of 17.5% has been achieved at 4 GHz in inverted AlGaN/GaN MODFET's (IMODFET's) with 2 /spl mu/m gate lengths and 78 /spl mu/m gate widths. The current gain and available power gain cutoff frequencies were 6 and 11 GHz, respectively. We suggest that the input characteristics of GaN-based FET's play an important role in the output power that can be obtained. In the present devices, high transconductance, 100 mS/mm, retained over a 5 V input swing is thought to alleviate the limitations imposed by the input characteristics. Moreover, the buried AlGaN buffer layer is suggested as having assisted in the reduction of the output conductance which aids the power gain.
IEEE Electron Device Letters 07/1997; · 2.85 Impact Factor
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ABSTRACT: AlGaN/GaN double heterostructure channel modulation doped field
effect-transistors (DHCMODFETs) with a 1.5-1.75 μm gate length and 3
μm channel length exhibiting record transconductances and saturation
current have been demonstrated. The maximum normalised drain current and
transconductance are ~1100 mA/mm and 270 mS/mm, respectively, at room
temperature. Near pinch-off, the drain breakdown voltage is ~80 V. At an
elevated temperature of 300°C, the maximum drain source current and
extrinsic transconductance of the device are ~500 mA/mm and 120 mS/mm,
respectively
Electronics Letters 05/1997; · 0.96 Impact Factor
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ABSTRACT: Current–voltage characteristics of AlGaN/GaN modulation doped field‐effect transistors at elevated temperatures are studied experimentally. The drain–source current and extrinsic transconductance are both found to decrease with increasing temperature. Decrease in mobility with increasing temperatures is considered to be one of the causes of the reduction in the current and transconductance. The capacitance–voltage characteristic reveals the absence of heat activated traps in the modulation doped layer. The physics underlying various high‐temperature operations of current–voltage characteristics is discussed. © 1996 American Institute of Physics.
Applied Physics Letters 01/1997; · 3.84 Impact Factor
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ABSTRACT: Gallium nitride is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Among the devices considered for high power generation is the ubiquitous field‐effect transistors which require Schottky barriers for modulating the channel mobile charge. It is in this context that we have undertaken an investigation of likely metal‐GaN contacts. Here we report on the electrical conduction and other properties of Pt–GaN Schottky diodes. These Schottky diodes were fabricated using n‐GaN grown by the molecular beam epitaxy method. Both capacitance–voltage and current–voltage measurements have been carried out as a function of temperature to gain insight into the processes involved in current conduction. Based on these measurements, physical mechanisms responsible for electrical conduction at low and high voltages and temperatures have been suggested. Schottky barrier height determined from the current–voltage and capacitance–voltage measurements is close to 1.10 eV. © 1996 American Institute of Physics.
Journal of Applied Physics 11/1996; · 2.17 Impact Factor
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ABSTRACT: Molecular‐beam‐epitaxial GaN layers change from strongly conductive (ρ≂10<sup>-2</sup> Ω cm at 300 K) to semi‐insulating (ρ≂10<sup>6</sup> Ω cm) as the N flux is increased. Layers grown at low fluxes show strong n‐type conduction, with transport in the conduction band at high temperatures and in a shallow donor band at low temperatures. For layers grown at high N fluxes, the Hall coefficients become too small to measure, suggesting hopping conduction among deep centers. The temperature‐dependent resistivity data are most consistent with multiphonon, rather than single‐phonon, hopping. © 1996 American Institute of Physics.
Journal of Applied Physics 10/1996; · 2.17 Impact Factor
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ABSTRACT: The emission and reflection spectra of GaN have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Three intrinsic exciton transitions have been observed, one associated with each of the valence bands. Exciton excited states associated with the two top valence bands were also observed. The exciton binding energies, the band‐gap energies, and the exciton Bohr radii are all reported along with the dielectric constant and the spin‐orbit and crystal‐field parameters for GaN. © 1996 American Institute of Physics.
Journal of Applied Physics 08/1996; · 2.17 Impact Factor
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D. G. Park,
M. Tao,
D. Li,
A. E. Botchkarev,
Z. Fan,
Z. Wang,
S. N. Mohammad,
A. Rockett,
J. R. Abelson, H. Morkoc,
A. R. Heyd,
S. A. Alterovitz
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ABSTRACT: We report the properties of silicon nitride films deposited by the electron cyclotron resonance remote plasma enhanced chemical vapor deposition method on Si substrates using SiH 4 and N 2 . The effects of nitrogen/silane gas ratio (R=N 2 /SiH 4 ), electron cyclotron resonance power, substrate temperature, and H on growth, refractive index, chemical composition, and etch rate were investigated. Nominally stoichiometric Si 3 N 4 films were obtained with a refractive index of 1.9∼2.0 at a wavelength of 632.8 nm. The etch rate of the films in a buffered HF solution (7:1) was low (∼0.7 nm/min) and increased with increasing H 2 gas flow rate and decreasing substrate temperature during deposition. Fourier transform infrared spectroscopy and high temperature thermal evolution experiments showed very small amounts of H in the films. A leakage current less than 100 pA/cm<sup>2</sup> at a field of 2 MV/cm, a resistivity of ≳4×10<sup>17</sup> Ω cm, and breakdown strengths of 6–11 MV/cm at a current density of 1 μA/cm<sup>2</sup> were observed. These properties are comparable to those of Si 3 N 4 prepared by conventional high temperature (700 °C) chemical vapor deposition. The performance of GaAs‐based field‐effect‐transistors in switching and power applications can be enhanced substantially by employing a metal‐insulator‐semiconductor structure. By taking advantage of an in situ process approach, insulator‐GaAs structures were successfully gated with excellent interfacial properties. © 1996 American Vacuum Society
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1996; · 1.34 Impact Factor
