Annealing of low-temperature grown semiconductors: material optimization for ultrafast all-optical gating

Summary form only given. Ultrafast all-optical gating with compact semiconductor devices requires materials with high absorption modulation, sub-picosecond response times, and low absorption in the fully saturated state (low nonsaturable losses). For the first time, we correlate the time response with the strength of the modulation in as-grown and annealed LT-GaAs. The modulation is very weak in as-grown LT-GaAs with sub-picosecond response times. We demonstrate that annealing substantially increases the modulation and preserves a fast, subpicosecond response, yielding a superior material for ultrafast all-optical gating. A qualitative model is presented which relates the material properties to the defect structure and the defect-related optical transitions in LT-GaAs. Based on this model, for the first time, guidelines are obtained for controlled defect engineering of non-stoichiometric semiconductors for applications in ultrafast nonlinear optics.