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 H2 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 microm/h are obtained at temperatures ∼760 C and with the CdTe source temperature at 827 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 in-situ 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