A new method for the growth of CdTe crystals for RT X-ray photon detectors in the 1-100 keV range

We report on the growth of thick CdTe layers on ZnTe/(100)GaAs hybrid substrates by the novel H2 transport vapour phase epitaxy (H2T-VPE) method. High crystalline quality (100)oriented CdTe single crystal epilayers can be fabricated under atmospheric pressure and at growth temperatures (T-D) in the 600-800°C interval. Double crystal X-ray diffraction measurements performed on epilayers thicker than 30 mu m show CdTe (400) peaks with FWHM<59 arcsec. CdTe samples grown under optimized conditions have mirror-like surfaces. Epilayers grown below 650°C are p-type and low resistive, but they turn n-type above 650°C, likely as a result of donor diffusion from the substrate. RT resistivities (rho) similar to 10^6 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 CdTc is demonstrated by the results of time-of-flight measurements performed at RT on Au/n-CdTe/n(+)-GaAs diode structures under reverse bias conditions.