Simultaneous Measurement of Minority-Carrier Lifetime in Single-Crystal CdTe Using Three Transient Decay Techniques

Minority-carrier lifetimes have simultaneously been measured on a single-crystal CdTe sample using three transient decay techniques. These measurements are microwave-reflection photoconductive decay (μ-PCD), time-resolved photoluminescence (TRPL), and transient free-carrier absorption (TFCA). The sample is a 0.8-mm-thick single-crystal CdTe sample from JX Nippon Mining & Metals USA, Inc., which is nominally undoped but has a hole concentration of about 2 - 3 × 10¹⁴ cm^-3. Excess carriers are generated using a Nd:YAG laser with 5-ns pulses, and lifetimes are measured at room temperature. Using 532-nm excitation, the decay curves show an initial short-lifetime component, as carriers are generated near the unpassivated front surface. While TRPL shows a short lifetime of ~7 ns, both μ-PCD and TFCA have relatively long single-exponential decays after the initial 100 ns response. These decay times, which are more dominated by the bulk lifetime after the initial surface recombination, are 190 ns for both μ-PCD and TFCA. Simultaneous measurements using twophoton (1064 nm) excitation show bulk-dominated recombination for all three techniques. Lifetimes for both μ-PCD and TFCA are 270 ns, while the TRPL lifetime, which still shows some surfacelimited initial decay, is 160 ns.