Spontaneous and Stimulated Carrier Lifetime (77°K) in a High-Purity, Surface-Free GaAs Epitaxial Layer

Abstract

A simple optical transmission and excitation technique is demonstrated for the measurement of extremely short excess carrier lifetimes in GaAs. The middle layer of an epitaxial n⁺/n/n⁺ sample, in which excess carriers tend to be confined to the center of the structure, is selectively excited optically and serves essentially as a surface‐free sample that exhibits the recombination properties intrinsic to bulk material. Excited from lower to higher level (77°K), this layer (N_d∼2−3×10¹⁵/cm³, μ=6340 cm²/V sec) varies continuously in carrier lifetime from τ≈10⁻⁹ sec (spontaneous recombination) to τ≈2×10⁻¹⁰ sec (stimulated recombination), as determined by the measured change in sample absorption caused by Burstein shift of the carrier quasi‐Fermi levels (carrier population). The carrier distribution and generation rate are shown to be quite uniform within the sample as a result of the inverse dependence of the absorption upon the carrier concentration.