Non-contact lifetime screening technique for HgCdTe using transient millimetre-wave reflectance

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Abstract
A non-contact lifetime screening technique for measuring excess carrier lifetime in HgCdTe (MCT) using transient millimetre-wave reflectance (TMR) is presented. The TMR system described is capable of measuring lifetimes ranging from or approximately=1*1016 cm-3) p-type material to >1 mu s found in low-doped (15 cm-3) n-type material. In TMR the reflected 90 GHz millimetre-wave (mm-wave) signal is proportional to a transient change in photoconductivity induced by a short (1.06 mu m) YAG laser pulse. The details of the TMR test system including the mm-wave circuit design are described. The system uses a computer controller for 80-300 K temperature control, x-y wafer translation and data acquisition and analysis. The TMR technique is shown to be equivalent to standard photoconductive decay. Applications of the technique, including MCT epilayer characterization by both frontside and backside illumination and in-process wafer characterization, are discussed. Spatial mapping of lifetime over an MCT wafer is demonstrated.