Defect energy levels in p-type GaAsBi and GaAs grown by MBE at low temperatures

Deep level defects in p-type GaAs1-xBix (x < 1%) and GaAs grown by molecular beam epitaxy at substrate temperatures of 330 degrees C and 370 degrees C have been characterized by deep level transient spectroscopy. We find that incorporating Bi into GaAs at 330 degrees C does not affect the total concentration of hole traps, which is similar to 4 x 10(16) cm(-3), comparable to the concentration of electron traps observed in Si-doped GaAsBi having a similar alloy composition. Increasing the growth temperature of the p-type GaAsBi (x = 0.8%) layer from 330 degrees C to 370 degrees C reduces the hole trap concentration by an order of magnitude. Moreover, the defects having near mid-gap energy levels that are the most efficient non-radiative recombination centers are present only in GaAsBi layers grown at the lower temperature. These new results are discussed in the context of previous measurements of n-type GaAs and GaAsBi layers grown under similar conditions.