Femtosecond spectroscopy of trapping and recombination processes in low temperature grown GaAs and InGaAs
Abstract
Femtosecond pump-probe spectroscopy was used to investigate carrier dynamics in low temperature grown (LT-) GaAs and (LT-) Ga0.47In0.53As. By using second harmonic generation, parametric conversion, and supercontinuum generation, we have employed the full power of femtosecond spectroscopy to monitor the fate of photoinjected carriers from thermalization and cooling to trapping and eventually recombination. In LT-GaAs, trapping rather than recombination was found to be responsible for the subpicosecond response at low carrier injection. Changes in the absorption coefficient and the refractive index were measured over a wide spectral range (2.7μm to 0.7μm) and over four decades of injected carrier densities (~1016[-]1020/ cm-3). We were able to identify the mid gap arsenic antisite (AsGa) defect as the main electron trap, with a concentration of ~2×1019/ cm-3, 3% of which are ionized. The gallium vacancy level (VGa) defect was found to be the main hole trap, with a concentration of ~5×1017/ cm-3. Despite trapping being faster in the as-grown material, recombination is more efficient in the annealed material. Recombination in the as-grown material is through defect mediated Auger processes, while it is controlled by the arsenic precipitates in the annealed material. Unlike normally grown layers, GaInAs grown at 200oC was found to have an ultrafast carrier scattering rate. This process spreads the injected carrier distribution producing a thermalized carrier distribution within our 100 fs time resolution. The band edge transient bleaching behavior in undoped layers grown at 200oC was qualitatively similar to that in the layer grown normally (i.e. @ 500oC). This is due to the presence of a shallow donor level and the lack of a significant density of ionized deep levels in the LT layers. The incorporation of Be dopant atoms during the low temperature growth drastically speeds the recovery of the absorption transient. Despite that, the recombination rate in LT-GaInAs was found to be similar to that of normally grown layers.
- Publication:
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Ph.D. Thesis
- Pub Date:
- October 1997
- Bibcode:
- 1997PhDT.......133L
- Keywords:
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- Physics: Condensed Matter, Physics: Optics, Engineering: Materials Science