Use of near-infrared as a screening technique for CdZnTe substrates

Epitaxial layers of CdxHg1-xTe (CMT) are grown onto Cd1-yZnyTe (CZT) substr ates in order to minimize misfit dislocations at the growth interface. For long wavelength focal plane array infrared detector requirements x = 0.22 C MT is nominally lattice matched to CZT alloys with y similar to 0.04. Howev er, the rate of change of lattice parameter, as a function of y, means that the uniformity and definition of the required Zn concentration is importan t. We report here a non-contact, non-destructive technique for screening/ma pping CZT substrates using the near infrared (NIR) band edge cut-on, define d by the wavelength corresponding to an absorption coefficient (alpha) = 10 cm(-1), which automatically corrects for thickness or transmission variati ons. Details of the experimental set-up and a novel holder for vertical mou nting of substrates are given. A comparison of results from this technique and X-ray diffraction (XRD) lattice parameter data is also presented.