ULTRAFAST CARRIER DYNAMICS IN III-V-SEMICONDUCTORS GROWN BY MOLECULAR-BEAM EPITAXY AT VERY LOW SUBSTRATE TEMPERATURES

Ultrashort carrier lifetimes were experimentally observed in a variety of As-based III-V crystalline semiconductor layers grown by molecular beam epitaxy over a range of very low substrate temperatures. Time-resolved optical absorption, reflection, and photoconductive switching measurements with femtosecond resolution have been used to directly measure the ultrafast carrier dynamics in these materials. GaAs and In0.52Al0.48As grown at temperatures of 200 and 150-degrees-C, respectively, exhibited subpicosecond carrier lifetimes, while lattice-mismatched InxGa1-xAs on GaAs displayed a 7 ps carrier lifetime in material grown at 200-degrees-C. A distinct decrease in carrier lifetime with decreasing growth temperature is documented for all three of the different material systems. For epilayers annealed at high-temperature, resistivities are high, and thus these materials were found to be ideally suited for a number of ultrafast optoelectronic applications. In addition to demonstrating the performance of the low-temperature-grown materials in simple photoconductive detectors, a number of these applications are reviewed and discussed.