Investigation of the Recombination and Trapping Processes of Photoinjected Carriers in Semi-Insulating Cr-Doped GaAs Using PME and PC Methods

Abstract

Investigation of the recombination and trapping processes of photoinjected carriers in semi-insulating Cr-doped GaAs (ρ ∼ 108 Ω cm) has been made at 80 and 300°K, using the photomagnetoelectric (PME) and photoconductive (PC) effects under large-injection conditions. A generalized theory for the PME and PC effects is developed, taking into account the variation of carrier lifetimes with injected-carrier density (i.e., τn = κΔnβ) and of the trapping of holes in the Cr levels (i.e., Δp = ΓΔn, Γ<1), by using a simple recombination and trapping model. The result yields a power-law relationship between the PME short-circuit current and the photoconductance, in a form that IPME varies as ΔG2/(2+β), valid for different injection ranges. Two well-defined ranges of injection were observed from the present results: In region I (high injection), IPME is directly proportional to ΔG (i.e., β = 0), and in region II (intermediate injection), IPME varies with ΔG1.2 (i.e., β = −⅓). Numerical values of τn, τp, and IPME as functions of ΔG are given. The results are in good agreement with the theoretical predictions.