Optical nonlinearity in low-temperature-grown GaAs: Microscopic limitations and optimization strategies

We have quantitatively measured the linear and the nonsaturable absorption as well as the absorption modulation and its recovery time in as-grown and annealed low-temperature (LT) GaAs. Correlation of the optical data with As antisite (As-Ga) defect densities yields the absorption cross section and the saturation parameter of the dominant As-Ga to the conduction-band defec t transition. We show that this defect transition is mainly responsible for the large nonsaturable absorption in as-grown LT GaAs with fast recovery t imes. Reducing the As-Ga density by annealing yields an optimized material with small nonsaturable absorption, high absorption modulation, and fast re covery times. (C) 1999 American Institute of Physics. [S0003-6951(99)03721- 3].