The impact of defects to minority-carrier dynamics in heavily doped GaAs:C analyzed by transient photoluminescence spectroscopy

We report photoluminescence decay time measurements in heavily Carbon-doped GaAs epilayers which are designed for the application in heterojunction bipolar transistors. These data provide access to carrier lifetimes that determine the current gains, i.e. amplification of the devices. At room-temperature trapping of non-equilibrium carriers into deep levels may govern the recombination behavior, particularly for low excitation levels. Experimental conditions are determined that allow both to achieve trap saturation and to avoid stimulated emission. Detection must be limited to a spectral window well above the energy gap. Our time-resolved data are explained by intrinsic Auger and radiative recombination mechanisms as well as defect-related recombination and trapping.