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Growth of epitaxial layers of Cd x Hg 1− x Te (CMT) onto Cd 1− y Zn y Te (CZT) substrates is widely reported as being performed in order to minimize misfit dislocations at the growth interface. The lattice parameters of CdZnTe alloys with y ∼0.04 are chosen to match that of x =0.22 CdHgTe. However, the rapid rate of change of lattice parameter, as a function y , means that the uniformity and definition of the required Zn concentration is potentially very critical. Segregation effects in the bulk growth process means that commercial CZT suppliers are unwilling to accept tight specifications on ` y ' and, in addition, different internal techniques and calibrations are being used to determine ` y '. Previously published studies of the nondestructive, near IR assessment of the CdZnTe band edge, required extrapolation techniques to define a cut-on point. Empirically determined correction factors were then applied to account for the effect of substrate thickness variations but no allowance was made for potential variations in the transmission value of the substrate. We report a study of the NIR band edge cut-on, defined by the wavelength corresponding to an absorption coefficient α =10 cm −1 , which automatically corrects for thickness or transmission variations. Data have been correlated against XRD lattice parameter data to determine the required Zn concentration. |
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