A MOVPE technology for fabrication of CdTe-based homoepitaxial p-i-n diode structures as nuclear radiation detectors

The homoepitaxy of n-CdTe:I layers is reported as a technological step towards the fabrication of CdTe-based p-i-n diode nuclear radiation detectors. CdTe:I layers were grown at 330°C on detector-grade (111)-oriented CdTe crystals by metalorganic vapour phase epitaxy. To ensure CdTe homoepitaxy, as-received substrates were treated before growth by etching in Br2-methanol and in-situ H2 heatcleaning at 350°C. (111)-oriented layers with fairly good surface morphology were obtained on as-prepared substrates by growing under Cd-rich vapour conditions. I-doped samples turned out to be n-type with resistivity values around a few Ω·cm and electron concentration ~1016 cm-3, but substantial electrical compensation of I donors occurs in the material, likely due to the formation of unintentional VCd-ITe acceptor centres. Homoepitaxial n-CdTe:I/i-CdTe samples were used to fabricate a preliminary Pt/i-CdTe/n-CdTe:I/Al device structure. Improvement of electrical insulation between back and front electrodes in this M-i-n device was achieved by reactive ion etching of the CdTe:I layer around the Al electrode. This treatment turned out to be effective in reducing the current flowing through the device under reverse bias conditions by more than one order of magnitude.