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 defect transition. We show that this defect transition is mainly responsible for the large nonsaturable absorption in as-grown LT GaAs with fast recovery times. Reducing the As(Ga) density by annealing yields an optimized material with small nonsaturable absorption, high absorption modulation, and fast recovery times. (C) 1999 American Institute of Physics. [S0003-6951(99)03721-3].