No abstract

Epitaxial GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures is observed to have a significantly shorter carrier lifetime than GaAs grown at normal substrate temperatures. Using femtosecond time-resolved-reflectance techniques, a subpicosecond (~0.4 ps) carrier lifetime has been measured for GaAs grown by MBE at-200°C and annealed at 600 "C. With the same material as a photoconductive switch we have measured electrical pulses with a full-width at half-maximum of 0.6 ps using the technique of electro-optic sampling. Good responsivity for a photoconductive switch is observed, corresponding to a mobility of the photoexcited carriers of-120-150 cm"/V s. GaAs grown by MBE at 200 "C! and annealed at 600 "C is also semi-insulating, which results in a low dark current in the switch application. The combination of fast recombination lifetime, high carrier mobility, and high resistivity makes this material ideal for a number of. subpicosecond photoconductive applications.

No abstract

We report the construction of a sensitive electro-optic sampling system for the measurement of ultrafast electrical transients. This system has a temporal resolution of lessthan 4 ps (over 100- GHz bandwidth), better than 50-μV sensitivity and potential for a temporal resolution reaching the single picosecond. Demonstrated applications are ultrafast photodetector response characterization and time resolved photoconductivity.