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

The homoepitaxy of n-CdTe:l 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 330degC 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 heat-cleaning at 350degC. (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 Omega^.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 V_Cd-l_Te acceptor centres. Homoepitaxial n-CdTe:I/i-CdTe samples were used to fabricate a preliminary Pt/i-CdTe/n-CdTe:I/AI 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.