Vertical Bridgman growth and characterization of CdMnTe substrates for HgCdTe epitaxy

A Cd_0.8Mn_0.2Te (CdMnTe) single-crystal ingot was grown by the vertical Bridgman method. The properties of the as-grown CdMnTe crystal required for substrate application of HgCdTe epitaxy, relating to the crystallinity, uniformity, impurity, and mechanical properties, were investigated. X-ray rocking curve and etch pits density (EPD) measurements revealed that the as-grown crystal had a full-width-at-half-maximum (FWHM) of 40-70 arcsec and EPD of (6-8)×10⁴ cm^-2, which indicated a high crystalline perfection. The distribution of Mn along the axial and radial directions of the ingot was measured by electron microprobe analysis. It was evaluated that the segregation coefficient of Mn in CdMnTe during the growth was 0.95, and the Mn concentration variation in the radial direction was within 0.001 mole fraction. The impurity segregation in the as-grown ingot was studied by inductively coupled plasma-mass spectrometry (ICP-MS). It was found that the impurities Li, Ni, and Ag with segregation coefficients larger than unit were enriched in the first-to-freeze region of the ingot, while the impurities In, Cu, and Ga with segregation coefficients less than unit were enriched in the last-to-freeze region of the ingot. Vickers microhardness measurements showed that the microhardness of the as-grown CdMnTe ingot was in the range of 52.2-56.0 kg/mm² and increased with the increase of Mn concentration.