Lifetime characterization of n-type HgCdTe under high excess carrier density conditions

Abstract

The excess carrier lifetime characterization of n-type HgCdTe under high excess carrier density conditions for both transient and steady state cases is discussed. Under low excess carrier density excitation, the excess carrier transport equations are linear and in the transient case the decay of the excess carriers is essentially exponential. At high excess carrier density excitation a departure from exponential decay is observed. An initial fast or slow decay is observed depending on initial conditions. Transient excess carrier lifetime results as measured by photoconductive decay are presented. The excess carrier density is generated by using a short (10 ns) 1.06 μm YAG laser pulse. Measurements are made over the 80–300 K temperature range. The results are compared with predictions from a three-level Shockley–Read model. In the model the three trap levels include a deep (approximately midgap) level and a compensating divalent Hg-vacancy acceptor. The donor level is assumed fully ionized. Steady state lifetime results within the framework of the model are also discussed. A drop in the steady state lifetime at high excess carrier density levels is predicted.