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ABSTRACT: We report on the results of transport studies of MBE-grown InAs/GaSb superlattices. We demonstrate that the in-plane mobility
is limited by interface roughness scattering by showing that, as a function of InAs layer width L, the in-plane mobility behaves
as μ ∝ L5.3, which closely follows the classic sixth power dependence expected from theory for interface-roughness-limited mobility.
Fits to the mobility data indicate that, for one monolayer surface roughness, the roughness correlation length is about 35
Å. Next, we show that the in-plane carrier mobility in InAs/GaSb superlattices is inversely proportional to carrier density
in n- and p-type samples, the result of screened interface roughness scattering.
KeywordsInAs/GaSb-superlattice-mobility-transport-interface roughness scattering
Opto-Electronics Review 04/2012; 18(3):267-270. · 0.97 Impact Factor
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ABSTRACT: The exposure of GaAs to laser ablated ZnTe causes the formation of donor (Te)-acceptor (Zn) pair states. The photonically transferred dopants resulted in a distinct transition at 1.378 eV (FWHM ≤ 30 meV), visualized by room temperature photocurrent spectroscopy. The presence of impurity absorption in the GaAs was confirmed by transmission measurements. Notably, from the standpoint of technological applications, flipping the applied bias (±1.0 V) to the ZnTe/GaAs heterostructure switches the spectral photocurrent response between the fundamental GaAs absorption and the donor-acceptor transition peak. The results further reveal the influence of the ablating laser line on the optoelectronic device properties.
Applied Physics Letters 09/2011; · 3.84 Impact Factor
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ABSTRACT: Efficient perpendicular transport of carriers by drift and diffusion in InAs/GaSb superlattice-based devices is necessary for achieving high device figures of merit. However, the values of perpendicular mobilities are usually inferred indirectly or through nonstandard experiments. Treating perpendicular and transverse mobilities on equal footing, we present here the results of a calculation of low-temperature perpendicular and transverse electron mobilities in InAs/GaSb superlattices as limited by interface-roughness scattering. Using the calculated mobility curves, it is possible to infer the value of the vertical mobility from measurements of the horizontal mobility.
Applied Physics Letters 05/2011; 98(18):182105-182105-3. · 3.84 Impact Factor
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ABSTRACT: We studied the emission properties of colloidal PbS quantum dots (QDs) (5.3 nm) dispersed on semi-insulating GaAs in the temperature range of 5–300 K by employing Fourier transform infrared photoluminescence spectroscopy. The results reveal that the PbS QDs alter and notably enhance the emission features of the GaAs substrate itself. The dependence of the QD emission peak position on temperature is modeled equivalently well with the well-known empirical Varshni equation and with a relation based on thermodynamics. The work reveals that emission properties of PbS QDs do not follow predictably general rules but are determined sensitively by the preparation method and substrate used.
Journal of Applied Physics 08/2010; · 2.17 Impact Factor
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ABSTRACT: We investigate the optical and electrical properties of a series of InAs/GaSb superlattices (SLs) as a function of InAs layer width d , from 21 to 55 Å, with a fixed GaSb layer width of 24 Å, corresponding to SLs with the cutoff wavelengths between 4 and 19 μ m . Since the higher electron mass in InAs/GaSb SLs than in mercury cadmium telluride should lead to lower photodiode tunneling currents, we also measured the cyclotron effective mass for a very long wavelength infrared design SLs. For d<40 Å , the SLs were p -type, with hole mobilities of approximately 8 000 cm <sup>2</sup>/ V s . For a high mobility p -type sample no hole cyclotron resonance signal was detected. However, the SLs with d≥40 Å were n -type, with electron mobilities increasing from 865 to 6126 cm <sup>2</sup>/ V s . Cyclotron resonance data on an n -type SL sample yielded an electron cyclotron mass of 0.068 m<sub>0</sub> , which is three times the InAs bulk value of 0.023 m<sub>0</sub> . The mass enhancement was only partially accounted for by conduction band nonparabolicity, based on our 8×8 envelope function calculation.
Journal of Applied Physics 05/2010; · 2.17 Impact Factor
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ABSTRACT: Reducing residual background carriers in InAs/GaSb superlattices (SLs) is an essential task to increase the operating temperature of photoconductive devices. This paper discusses how low-temperature Hall measurements were used to tune several SL growth parameters for the minimum residual carriers in a typical midinfrared 21 Å InAs /24 Å GaSb SLs designed for the 4 μ m cutoff wavelength. Among the three growth parameters studied, neither growth temperature nor in situ postannealing significantly affected the intrinsic carrier type and doping concentration. The lowest carrier density of 1.8×10<sup>11</sup> cm <sup>-2</sup> was achieved at 400 ° C . All SLs grown at 400 ° C maintained the lowest density around 1.6×10<sup>11</sup> cm <sup>-2</sup> with or without postannealing. However, in-plane carrier mobility showed a slight improvement with annealing, especially at temperatures above 450 ° C . The growth parameter most sensitive to the carrier density was interface control. With a minor variation in interface shutter sequence, the carrier density dramatically increased from ∼2×10<sup>11</sup> to 5×10<sup>12</sup> cm <sup>-2</sup> , and the corresponding mobility dropped from 6600 to 26 cm <sup>2</sup>/ V s , indicating dramatic degradation of interfacial quality. All SLs investigated in this study were residually p -type.
Journal of Applied Physics 11/2008; · 2.17 Impact Factor
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ABSTRACT: This paper presents an analysis of indium arsenide–gallium antimonide (InAs/GaSb) (110)-grown superlattices for use as infrared detectors. The analysis shows that InAs/GaSb superlattices grown on (110)-oriented substrates can be grown thinner, have higher mobilities, longer diffusion lengths, greater quantum efficiencies, and gains, thus higher responsivities, than those grown on (100)-oriented substrates for the same long wavelength threshold. Based on growth studies to date, (110) superlattices should also have higher minority carrier lifetimes, lower noise, and lower residual carrier densities, thus higher detectivities. The calculated electronic structure of a (110)-oriented superlattice based on the 8×8 envelope-function approximation shows the bands to be anisotropic and the oscillator strengths to be polarization dependent. Recommended layer widths for specific absorption thresholds are calculated.
Journal of Applied Physics 11/2008; · 2.17 Impact Factor
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ABSTRACT: Using a newly developed envelope function approximation model that includes interface effects, several InAs/GaSb type-II superlattices (SLs) were designed for uncooled mid-infrared detector applications. The 4 micron cutoff could be achieved with several SL designs. Superlattices with shorter periods have larger intervalence band separations than larger-ones, which could increase the optical signal and reduce the detector noise, thus making room temperature operation possible. To test these possibilities, several short-period SLs were grown by molecular-beam epitaxy and their optical properties with reducing SL period were studied by band-edge absorption, photoconductivity and photoluminescence measurements. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 04/2007; 4(5):1702 - 1706.
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ABSTRACT: The in-plane transport in InAs/GaSb type-II superlattices (SLs) is a sensitive indicator of SL growth quality and of the eventual performance of devices made from these materials. The in-plane mobility of electrons that move predominantly in the InAs layer is affected by a number of intrinsic and extrinsic scattering mechanisms, including interface roughness scattering (IRS). The hallmark of classic IRS-limited transport in SLs and quantum wells is the sixth power dependence of mobility on layer width. While IRS-limited transport was demonstrated in a number of SL and quantum well systems, it has never been demonstrated in the important InAs/GaSb SL material. In this paper, we perform temperature dependent Hall effect measurements on a series of InAs/GaSb SLs with a fixed GaSb layer width and a variable InAs layer width d. The low temperature (10 K) in-plane electron mobilities μ as a function of d behave as μ∝d6.20, which follows the classic sixth power dependence expected from theory. At the same time, the dominance of the IRS-limited transport indicates that our samples are less affected by other scattering mechanisms, so that mobility measurements are another indicator of sample quality.
Journal of Applied Physics 02/2007; 101(4):043706-043706-5. · 2.17 Impact Factor
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ABSTRACT: The realisation of an InGaAs/InP quantum-well infrared photodetector focal plane array imaging device is reported. The long-wave infrared response is based on the intersubband transition (intraband) in the quantum wells. In addition, a near infrared (interband) response is demonstrated. This work shows the potential of the InGaAs/InP materials system for multi-spectral imaging applications
Electronics Letters 02/2007; · 0.96 Impact Factor
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ABSTRACT: The effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design
of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that
incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb
interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb
layers as thin as a few monolayers. Although the oscillator strengths are predicted to be larger for thinner period superlattices,
the absorption coefficients are comparable because of the compensating effect of larger band widths. However, larger intervalence
band separations for thinner-period samples should lead to longer minority electron Auger lifetimes and higher operating temperatures
in p-type SLs. In addition, the hole masses for thinner-period samples are on the order the free-electron mass rather than
being effectively infinite for the wider period samples. Therefore, holes should also contribute to photoresponse. A number
of superlattices with periods ranging from 50.6 to 21.2 Å for the 4 μm detection threshold were grown by molecular beam epitaxy
based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band
gaps remained constant at 330 meV although the period changed by the factor of 2.5. Overall, the present study points to the
importance of interfaces as a tool in the design and growth of thin superlattices for mid-IR detectors for room temperature
operation.
Opto-Electronics Review 02/2006; 14(1):69-75. · 0.97 Impact Factor
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ABSTRACT: Using a newly developed envelope function approximation model that includes interface effects, several In As / Ga Sb Type-II superlattices (SLs) were designed for the 4 μ m detection threshold. The present model predicts that a given threshold can be reached with a wide range of progressively thinner SL periods and these thinner designs hold a promise of higher mobilities and longer Auger lifetimes, thus higher detector operating temperatures. The proposed SL structures were grown by molecular-beam epitaxy with slow growth rates. As predicted, the band gaps of SLs determined by low-temperature photoluminescence remained constant around 330 meV for the samples in the period range from 50.6 to 21.2 Å .
Applied Physics Letters 01/2006; · 3.84 Impact Factor
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Microelectronics Journal. 01/2005; 36:256-259.
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ABSTRACT: The superlattice (SL) of a 40 period InAs / GaSb SL structure were varied around the 20.5 Å InAs /24 Å GaSb design in order to produce a device with an optimum mid-infrared photoresponse and a sharpest photoresponse cutoff. The samples for this study were grown by molecular beam epitaxy with precisely calibrated growth rates. Varying individual layer width around the nominal design, we were able to systematically change the photoresponse cutoff wavelength between 4.36 to 3.45 um by decreasing the InAs width from 23.5 to 17.5 Å , and between 4.55 to 4.03 μ m by increasing the GaSb width from 18 to 27 Å . Therefore, the cutoff changes faster with decreasing InAs rather than increasing GaSb width. However, increasing GaSb width more effectively enhances the sharpness of photoresponse near band edge. The effect of design parameters on the photoresponse cutoff and other effects are explained by a nonperturbative, modified envelope function approximation (EFA) calculation that includes the interface coupling of heavy, light, and spin-orbit holes resulting from the in-plane asymmetry at InAs / GaSb interfaces. Using the modified EFA model, the SL design at fixed period of 44.5 Å was adjusted for the optimum performance.
Journal of Applied Physics 10/2004; · 2.17 Impact Factor
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ABSTRACT: The effect of small changes in GaSb layer width on the photoresponse spectrum of 20.5 Å InAs / InSb - interfaces /X Å GaSb type-II superlattice ( SL ) suitable for mid-infrared detection was investigated. By decreasing the GaSb width X from 27 to 18 Å , the cut-off wavelength was increased from 4.03 to 4.55 μ m . This decrease of the SL band gap and other effects of the design changes on photoresponse spectrum with narrower GaSb layers are explained by a nonperturbative, modified envelope function approximation calculation that includes the interface coupling of heavy, light, and spin–orbit holes resulting from the in-plane asymmetry at InAs / GaSb interfaces.
Applied Physics Letters 07/2004; · 3.84 Impact Factor
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ABSTRACT: Optimum bound-to-continuum normal-incidence absorption in low-doped (less than 1×1012cm-2) p-type GaAs/AlGaAs quantum wells obtains for well widths for which the second light-hole (LH2) level is resonant with the top of the valence band quantum well near the center of the Brillouin zone. Experimentally we found that such absorption saturates at higher doping levels. For higher doping around 4×1012cm-2, our envelope-function approximation (EFA) model predicts that pushing LH2 deeper into the continuum avoids absorption saturation and at least doubles the photoresponse. The results are explained on the basis of an EFA calculation, which shows that saturation is due to the fact that the line of resonances in the continuum as a function of the in-plane wave vector eventually becomes a bound LH2 band in the well at some critical wave vector. By matching this critical wave vector (via well width and/or well depth adjustment) with the Fermi wave vector (determined by doping in the well) for the desired QWIP (i.e., cutoff wavelength), saturation can be avoided. This prediction is verified on a set of well-characterized samples. A re-entrant band behavior, in which a band is bound over a limited portion of the Brillouin zone, is also demonstrated.
Phys. Rev. B. 08/2003; 68(8).
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ABSTRACT: Using a set of p-type GaAs/AlGaAs quantum well infrared
photodetectors, a wide spectral coverage is demonstrated. Photoresponses
at wavelengths as short as 1.4 μm and as long as 15 μm are shown.
The shortest wavelength device with a high Al fraction (95%) peaks at
1.9 μm and covers a range of 1.4 to 3 μm
Electronics Letters 09/2002; · 0.96 Impact Factor
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ABSTRACT: The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are
presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately
7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam
epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors
grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength.
The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than
superlattices grown on GaSb substrates.
Journal of Electronic Materials 06/2001; 30(7):798-801. · 1.47 Impact Factor
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ABSTRACT: Resonant cavities are used to enhance the absorption efficiency in p-type GaAs/AlGaAs quantum-well infrared photodetectors. The cavities are fabricated by applying thick gold films on the detector bottom sides after substrate removal via selective wet etching. The observed peak enhancement and spectral shape are in good agreement with model predictions. Peak absorption of about 25% is obtained for the device studied. © 2000 American Institute of Physics.
Applied Physics Letters 10/2000; 77(15):2400-2402. · 3.84 Impact Factor
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ABSTRACT: We report a demonstration of very long wavelength infrared detectors based on InAs/GaSb superlattices operating at T = 80 K. Detector structures with excellent material quality were grown on an optimized GaSb buffer layer on GaAs semi-insulating substrates. Photoconductive devices with 50% cutoff wavelength of λc = 17 μm showed a peak responsivity of about 100 mA/W at T = 80 K. Devices with 50% cutoff wavelengths up to λc = 22 μm were demonstrated at this temperature. Good uniformity was obtained over large areas even for the devices with very long cutoff wavelengths. © 2000 American Institute of Physics.
Applied Physics Letters 09/2000; 77(11):1572-1574. · 3.84 Impact Factor
