Vapor phase epitaxy growth of CdTe epilayers for RT x-ray detectors

We report on the growth of thick CdTe layers on ZnTe/(100)GaAs hybrid substrates by the novel H2 transport vapor phase epitaxy, (H2T-VPE) method. High crystalline quality (100)-oriented CdTe single crystal epilayers can be fabricated under atmospheric pressure and at growth temperatures (TD) in the 600-800°C interval. Double crystal X-ray diffraction measurements performed on epilayers thicker than 30 mum show CdTe (400) peaks with FWHM<59 arcsec. Samples grown under optimized conditions exhibit mirror-like surfaces. Nominally undoped epilayers grown <650°C are p-type and low resistive, but they turn n-type above 650°C, as a result of donor (likely Ga) diffusion from the substrate. RT resistivities (rho) around 10^5 Ohm.cm are obtained for 675°C<TD<700°C, but rho decreases for higher temperatures and thinner samples. Layers grown under these conditions show RT electron concentrations in the 10^14-10^11 cm^-3 range. The detection capability of H2T-VPE grown CdTe is demonstrated by time-of-flight measurements performed at RT on Au/n-CdTe/n(+)-GaAs diode structures under reverse bias conditions. The present results show the potentials of H2T-VPE for the growth of detector-grade CdTe.