CHARACTERIZATION OF CDTE SUBSTRATES AND MOCVD CD1-XZNXTE EPILAYERS BYRAMAN, PHOTOLUMINESCENCE AND X-RAY-DIFFRACTION TECHNIQUES

CdTe substrates and the quality of the Cd1-xZnxTe (x less than or equa l to 0.1) epilayers grown by metalorganic chemical vapor deposition (M OCVD) on CdTe substrates, are characterized by Raman scattering and ph otoluminescence (PL) as well as by X-ray double-crystal rocking curve (DCRC). At a low temperature the intensity of LO phonon is enhanced wh erever there is a structural defect. The defect-induced enhancement is due to a large momentum transfer which enhances the intraband Frolich interaction. In addition, the bound exciton peak intensity measured b y PL decreases wherever the LO phonon scattering efficiency increases confirming that the defect is the origin of the above Raman enhancemen t. The quantitative measure of the structural perfection is related to the ratio between the defect band and excitonic peaks in the PL spect ra, and correlates with the X-ray full-width at half-maximum (FWHM) of the layer peak. It is shown that in addition to these parameters, the FWHM of the PL defect band is a useful parameter to determine the qua lity of the epilayer, and a good correlation is obtained between the d ifferent parameters. The effect of growth parameters such as zinc part ial pressure in the reactor during growth and the reactor design are s tudied. The results indicate that crystalline imperfection is caused b y lattice mismatch between the CdTe substrate and the CdZnTe epilayer and by the nonuniformity of the zinc composition throughout the layers . The quality of the layers is independent of the reactor volume. (C) 1998 Elsevier Science B.V. All rights reserved.