Subpicosecond carrier lifetime in GaAs grown by molecular beam epitaxy at low temperatures

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 sub-picosecond (<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 cm2/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.