Quality assessment of CdZnTe (Zn ∼ 4 %) crystals

We have studied the as grown and annealed CdZnTe (Zn ∼ 4 %) crystals for the assessment of their crystalline quality. As grown crystals suffer from tellurium precipitates and cadmium vacancies, which are inherent, due to retrograde solid solubility curve in the phase diagram. This is reflected in the Fourier transform infrared (FTIR) spectra over the 400 – 4500 cm
⁻¹
range by a strong absorption around 2661 cm
⁻¹
which corresponds to the band gap of tellurium confirming their presence, whereas a monotonic decrease in the transmission with the decrease in wave number indicates the presence of cadmium vacancies. Obviously the presence of Cd vacancies lead to the formation of tellurium precipitates confirming their presence. Annealed samples under cadmium + zinc ambient at 650 °C for 6 hours show an improvement in the transmission over the same range. This can be attributed to thermo-migration of tellurium precipitates and hence bonding with Cd or Zn to form CdZnTe. This is further supported by the reduced full width at half maximum in the X-ray diffraction rocking curve of these CdZnTe crystals. Cadmium annealing although can passivate Cd vacancy related defects and reduce the Te precipitates, as is observed in our low temperature Photoluminescence (PL) spectra, alone may not be sufficient possibly due to the loss of Zn. Vacuum annealing at 650 °C for 6 hours further deteriorated the material quality as is reflected in the low temperature PL spectra by the introduction of a new defect band around 0.85 eV and reduced IR transmission.