Pump-probe spectroscopy of low-temperature grown gaAs for carrier lifetime estimation: Arsenic pressure dependence of carrier lifetime during MBE crystal growth

We have performed reflection-type degenerate pump-probe spectroscopy to measure the carrier lifetime of GaAs grown by molecular beam epitaxy (MBE) at 250°C under four different effective arsenic pressures. The temporal behavior of the reflected probe pulse intensity strongly depends on both the wavelength and the intensity of the exciting laser pulse. The overall feature can be interpreted by the carrier-density- and wavelength-dependent refractive index change caused by the bandgap shrinkage, band filling, and plasma effect. We also found that the carrier lifetime depends on the effective arsenic pressure during the MBE growth, which is considered to determine the density of the defects in the GaAs. A carrier lifetime of 1.9 ps was obtained when GaAs was grown under the highest effective arsenic pressure at 250°C and subsequently annealed at 650°C.