Hydrogen transport vapor phase epitaxy of CdTe on hybrid substrates for x-ray detector applications

The growth of thick CdTe epitaxial layers by the hydrogen transport vapor phase epitaxy (H2T-VPE) method is reported for the first time. The thermodynamics of the H-2 transport method of CdTe is analyzed to determine the equilibrium partial pressures of the molecular species in the vapor and its supersaturation as a function of growth conditions. (100)-oriented CdTe epilayers are successfully grown by H2T-VPE on hybrid ZnTe/GaAs(100) substrates prepared by metalorganic vapor phase epitaxy. Growth rates up to 10 mu m/h are obtained at temperatures similar to 760 degrees C and with the CdTe source temperature at 827 degrees C. The achievement of even higher growth rates can be foreseen by using the present method under slightly different conditions; several hundreds micron thick CdTe layers can be thus grown by the H2T-VPE. CdTe samples have mirror-like, nearly featureless surfaces. Also, CdTe epilayers have shown a medium-to-high resistivity at room temperature, possibly as a result of compensation by donor impurities diffusing from GaAs. Still the growth of highly resistive layers by insitu chlorine doping during the H2T-VPE growth is possible. In summary, H2T-VPE is a potential alternative to traditional melt- and vapor-growth methods for the synthesis of detector-grade CdTe for application to the 1-100 keV x-ray energy range.