Cu(In,Ga,Al)Se-2 (CIGAS) thin films were studied as an alternative absorber layer material to Cu(InxGa1-x)Se-2. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350 degrees C, followed by postdeposition annealing at 520 degrees C for 5 h in vacuum. The film composition was measured by an electron probe micro-analyzer while the elemental depth profiles were determined by secondary ion mass spectrometry. X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2 theta values with increasing Al content. Scanning electron microscopy images revealed dense and well-defined grains, as well as sharp CIGAS/Si(100) interfaces for all films. Atomic force microscopy analysis indicated that the roughness of CIGAS films decreases with increasing Al content. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as Al content increased. (C) 2015 American Vacuum Society.

In the effective mass approximation, electronic structures of InAs/GaAs quantum rings are studied by the six-band k . p model. In the description of the Hamiltonian matrix elements, a Fourier transform method is adopted to replace analytical integral method in the literature. We demonstrate the energy levels as functions of geometric parameters of the rings and compare our results with those obtained by analytical integral. The remarkable consistency in the comparison certifies our results. The outcomes of the six-band k . p model in this article are also compared with those of the four-band k . p model. It is found that both the bound state energies and the transition energy are lower in six-band calculation than those in four-band calculation, which is attributed to the spin-orbit splitting in the six-band k . p model. (C) 2010 Elsevier Ltd. All rights reserved.

InAs single hetero structure photodiodes were considered as alternatives to cooled CdHgTe-based detectors sensitive to radiation around 3 mu m spectral region in a wide temperature range 77-300 K. Estimations of detectivity as well as p-n junction position in InAs heterostructures have been obtained via photo-electrical and AFM measurements.

We report dielectric function data from 0.74 to 6.54 eV for InAs at 22 K, obtained by spectroscopic ellipsometry. Critical-point (CP) structures are blueshifted and significantly sharpened relative to those seen at room-temperature (RT). The E(0)', E(2)(Delta), E(2), E(0)' + Delta(0)', and E(2)' features in the E(2) energy range of 4.0 to 5.6 eV cannot be resolved at RT but are clearly separated at 22 K. The energies of the CPs giving rise to these structures are determined by line shape fitting to numerically calculated second energy derivatives, and their Brillouin-zone locations identified by band structure calculations using the linear augmented Slater-type orbital method. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506497]

The findings of a study of impact ionization, avalanche multiplication and excess noise in InAs avalanche photodiodes at 77 K are reported. It is shown that hole impact ionization is negligible in practical devices which continue to operate as electron avalanche photodiodes, as they do at room temperature. A new electron ionization coefficient capable of modeling multiplication at 77 K is presented and it is shown that significant multiplication can be achieved in practical devices without excessive tunneling currents. The characteristic changes observed between room temperature and 77 K are discussed. This paper helps to demonstrate the potential for practical InAs electron avalanche photodiodes, operating cooled.

High-temperature operating performance of p-i-p quantum dots-in-awell infrared photodetectors (QDIPs) is successfully demonstrated. The optically active region consists of 10 layers of p-doped selfassembled InAs quantum dots (QDs) asymmetrically positioned in In0.15Ga0.85As quantum wells (QWs). The dark current is suppressed by an incorporated superlattice (SL) structure composed of 10 pairs of AlGaAs/GaAs heterostructure. The very low recorded dark current makes the fabricated p-i-p QDIPs suitable for high-temperature operation. The measured photoresponse reveals broad mid-wave infrared (MWIR) detection up to 200 K.

The electroluminescence of InAs/InAsSbP and InAsSb/InAsSbP LED heterostructures grown on InAs substrates is studied in the temperature range T =3D 4.2-300 K. At low temperatures (T =3D 4.2-100 K), stimulated emission is observed for the InAs/InAsSbP and InAsSb/InAsSbP heterostructures with an optical cavity formed normal to the growth plane at wavelengths of, respectively, 3.03 and 3.55 mu m. The emission becomes spontaneous at T > 70 K due to the resonant "switch-on" of the CHHS Auger recombination process in which the energy of a recombining electron-hole pair is transferred to a hole, with hole transition to the spin-orbit-split band. It remains spontaneous up to room temperature because of the influence exerted by other Auger processes. The results obtained show that InAs/InAs(Sb)/InAsSbP structures are promising for the fabrication of vertically emitting mid-IR lasers.

We have investigated carrier spin relaxation in InAs columnar quantum dots (CQDs) using time-resolved photoluminescence measurement. The CQDs were formed by depositing a 1.8 monolayer InAs seed dot layer and a short-period GaAs/InAs superlattice (SL). The spin relaxations of the 3 and 35-period SL CQDs show double exponential decay up to 50 and 130 K, respectively. The spin relaxation times of the fast component, whose amplitudes are 4-11 times larger than that of the slow component, are around 100 Ps for the two samples. For the 3-period SL CQDs, the fast spin relaxation time shows no temperature dependence up to around 50 K, indicating the relevance of the Bir-Aronov-Pikus process. The slow spin relaxation time of the 35-period SL CQDs was found to decrease from 3.42 ns at 10 K to 0.849 ns at 130 K. This large change may be explained by the Elliott-Valet process considering acoustic phonon scattering.

A spin-polarized vertical cavity surface emitting laser, with InAs/GaAs self-organized quantum dots as the active gain media, has been fabricated and characterized. Electron spin injection is achieved via a MnAs/GaAs Schottky tunnel contact. The laser is operated at 200 K and, at this temperature, the degree of circular polarization in the output is 8% and the maximum threshold current reduction is 14%. These effects are not observed in identical control devices with nonmagnetic contacts. (C) 2008 American Institute of Physics.

We fabricated a microdisk laser with five-stacked InAs quantum-dot (QD) active region, and demonstrated the lasing operation from 3 K to room temperature by femtosecond pulsed photopumping. At room temperature, the threshold power was estimated to be 0.75 mW, when the influence of the surface recombination at the disk edge was neglected. The lasing wavelength was 1.2–1.3 μm, which corresponded to excited states of the QDs. The temperature dependence of the threshold, slope efficiency, lasing wavelength, and linewidth are explained by the rapid increase in nonradiative recombination and internal absorption at critical temperatures of 200–230 K. ?2004 American Institute of Physics