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 In/sub 0.52/Al/sub 0.48/As grown at temperatures of 200 and 150 degrees C, respectively, exhibited subpicosecond carrier lifetimes, while lattice-mismatched In/sub x/Ga/sub 1-x/As 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 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. A number of applications are reviewed and discussed.>