Effect of growth conditions on crystalline quality of metalorganic chemical vapor deposition (111)B CdTe epilayers characterized by x-ray diffraction

Abstract

A study of the effect of growth parameters on the resulting crystalline quality of CdTe epilayers grown by metalorganic chemical vapor deposition (MOCVD) technique is reported. The crystalline quality of the MOCVD CdTe (111)B epilayers is investigated by the double crystal rocking curve (DCRC) and Laue x-ray diffraction techniques. The rocking curve full width at half-maximum (FWHM) is used as a quantitative measure of structural perfection of the epilayers. The results indicate that a major parameter that affects the crystalline quality is the growth temperature. Epilayers grown at 480 °C exhibit high crystalline quality that is hardly affected by the partial vapor pressure of the metalorganic sources or the growth rate, whereas these growth parameters strongly affect the crystalline quality of epilayers grown at 430 °C. This phenomenon is attributed to the different mechanisms governing the growth process at these growth temperatures, namely mass transfer and surface kinetics. The crystalline quality of the MOCVD CdTe layers grown on the (111)B face of CdZnTe (4% Zn) or CdTe substrates can consistently match that of MOCVD (001) layers previously considered to have the best crystalline quality, with FWHM less than 90 arcsec for 6–7 μm thick layers. Linewidths as narrow as 56 arcsec are observed for epilayers thicker than about 11 μm. Microtwins, identified by the sixfold symmetry of Laue and double crystal 360° φ-scan diffraction patterns, are present even in epilayers with the narrowest FWHM. No straightforward correlation between visual morphology and crystalline quality was found. The growth of CdTe or CdZnTe epilayers is proposed by the MOCVD technique as buffer layers to obtain super substrates (‘‘superstrates’’) for the subsequent liquid phase epitaxy (LPE) growth of HgCdTe layers and additional heterostructures.