MOVPE growth optimisation of CdTe epitaxial layers for p-i-n diode X-ray detector fabrication

We report on the atmospheric pressure metalorganic vapour phase epitaxy of both nominally undoped and iodine (I) donor doped CdTe layers on high resistivity (111)B CdTe substrates, as a preliminary step towards the fabrication of p-i-n diode X-ray detectors. CdTe epilayers were grown at 330°C after in-situ H2 heat treatment of the substrate for surface oxide removal. We show that the homoepitaxy of CdTe critically depends on in-situ heat treatment temperature (TA), best epilayer morphology and reduced surface roughness being obtained for TA = 350°C. Secondary ion mass spectrometry analysis of I-doped samples shows good dopant incorporation, which increases for Te:Cd precursor molar flow ratios in the vapour below unity. I-doped samples grown under the latter conditions have room temperature resistivity three orders of magnitude lower than for undoped layers and electron concentrations ~1016 cm-3.