Effects of CZT Substrate Surface Treatment on IR-Transmittance in the Annealing Process

The application of CdZnTe(CZT) crystals in infrared focal plane detectors and x-ray imaging detectors is hindered by the low infrared transmittance (IRT) and the presence of Cd/Te inclusions/precipitation. Over the preceding decades, strategies involving Cd vapor control during the growth process and substrate post-annealing have been posited to address these challenges. Presently, the prioritized approach is the utilization of substrate post-annealing, owing to the limited precision in comprehending the Cd-Te equilibrium and the intricacies associated with Cd vapor control technology. This study delves into the effect of the removed surface layer depth of a CZT and the selection of the (111) A-face or (111) B-face on IRT during Cd atmosphere annealing. It is recommended that a minimum of 60 μm of the surface layer be eliminated using chemical mechanical polishing technology before annealing. Experimental findings further reveal that Cd atom diffusion from the (111) A-face results in an IRT enhancement of up to 60%, in stark contrast to the slight improvement observed with the (111) B-face after annealing. The mechanism of Cd atom diffusions affecting the IRT in the annealing process is discussed.