INVESTIGATION OF FIELD, CARRIER, AND COHERENT PHONON DYNAMICS IN LOW-TEMPERATURE-GROWN GAAS

We compare the dynamics of electric field, transport, and coherent pho nons in as-grown and annealed low-temperature (LT) GaAs by an electro- optic technique on a subpicosecond time scale. The buildup and decay o f space-charge fields associated with the photo-Dember effect are inve stigated. The recombination dynamics of trapped carriers is monitored via the ps decay of the electro-optic signal. Differences in annealed and as-grown LT GaAs are related to the different microscopic form of excess arsenic and point defect density. In the coherent phonon signal a large red shift of the LO phonon and an additional local vibration below the LO phonon provides information on structural defects in as-g rown LT GaAs.