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In this work, we show that extraction of the true bulk lifetime from the biexponential decay that follows from low initial carrier density photoluminescence decay experiments is not generally possible, and introduce new models to enable extraction of the bulk lifetime in the case where the initial carrier density exceeds the doping level. From measurements with high initial carrier density, we establish quasi-equilibrium between localized and free carrier states and accurately measure the bulk lifetime. Using our new models, we measure the time constants associated with localization processes as well as nonradiative and radiative bulk recombination in our GaAs double heterostructures grown with molecular beam epitaxy from experiments with varied excitation strength providing initial carrier densities that range from around 1014 to 1017 cm-3. We demonstrate that this approach can be applied to lightly doped (1016 cm-3) materials where the strongest excitation yields initial carrier densities that exceed the doping level. In our n-type sample, we report lifetime values of (22.7±0.1) ns for bulk recombination, (73±1) ns for trap-capture, (51±2) ns for trap-emission, and (63±2) ns for trap-decay, with a low-level injection effective radiative efficiency of (27.5±0.7)%. In our p-type sample, we report lifetime values of (78.9±0.3) ns for bulk recombination, (77.5±0.7) ns for trap-capture, (530±10) ns for trapemission, and (177±4) ns for trap-decay, with a low-level injection effective radiative efficiency of (47.0±0.8)%. In comparison with the long and short lifetimes extracted from the biexponential decay with weak excitation, the mean bulk lifetime measured with strong excitation was (33±2)% and (53±1)% longer than the short lifetime, and (68±4)% and (103±3)% shorter than the long lifetime in our n-type and p-type samples, respectively. In our n-type sample, the extracted lowlevel injection nonradiative lifetime was (33±1) ns, and it was observed to remain constant with the injection level. In our p-type sample, the high-level injection nonradiative lifetime was measured to be (30±30)% larger than the low-level injection nonradiative lifetime of (140±2) ns. [ABSTRACT FROM AUTHOR]

In this work, we have decoupled the radiative and nonradiative contributions to recombination by developing analytical models to fit observed non-monoexponential photoluminescence decay and bulk-lifetime temperature-dependence, which has enabled absolute measurement of the effective radiative efficiency and characterization of the dominant defect in lightly doped GaAs samples grown using molecular-beam-epitaxy. The measured effective radiative efficiency values under low level injection conditions range from (88.9 ± 0.1)% and (81.2 ± 0.1)% at 77K to (0.028 ± 0.001)% and (0.034 ± 0.001)% at 700 K, with 300K values of (17.3 ± 0.1)% and (10.5 ± 0.1)% in the p-type and n-type samples, respectively. A common defect-signature is observed in the temperaturedependence of the nonradiative lifetime in samples of both doping types, and our measured parameters are consistent with characteristics previously measured for the EL2 defect using deep-level transient spectroscopy. [ABSTRACT FROM AUTHOR]

The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSb islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates. [ABSTRACT FROM AUTHOR]

We examine the role of vicinal surface steps in the formation and propagation of twins during the growth of epitaxial III-V thin films (GaAs, InP, GaSb, AlSb) on silicon substrates. This is achieved through the combined use of two-dimensional X-ray diffraction and conventional transmission electron microscopy techniques, which allow for both a macro and nano/micro characterization of the material systems. Observed is a systematic suppression of twins formed opposite to the tilt direction of vicinal substrates through a process of step-flow overgrowth of nucleated twins, and an enhancement of twins toward the tilt direction when the fastest growth planes are aligned with the step-flow. These results indicate a probable path to the enhancement of the electronic mobility of lateral devices based on III-V semiconductors on silicon. [ABSTRACT FROM AUTHOR]