Comparative study of In/CdTe/Au Schottky- and p–n junction-diode detectors formed by backside laser irradiation doping

Abstract

Two types of In/CdTe/Au diode structures were fabricated using detector-grade p-CdTe single crystals: (i) by vacuum evaporation of In and Au contacts on the chemically treated (111) surfaces; (ii) by backside laser doping when the In/CdTe structures were irradiated from the crystal side with a wavelength for which the semiconductor was transparent. Thus, diodes with a Schottky contact (In/CdTe) and a p–n junction were obtained, respectively. To prove the doping of the thin region near the In/CdTe interface by In (donor) and study thermal tolerance of both types of In/CdTe/Au diode detectors, room temperature I–V characteristics and 57Co isotope emission spectra were measured before and after annealing of the diodes at temperatures below and above the In melting point. Thermal annealing at lower temperatures led to a slight increase and decrease in reverse dark current of the unirradiated and laser-irradiated samples, respectively. Heating up to 200 °C resulted in a significant increase in reverse current and complete spectra degradation in the samples fabricated without laser processing. After such annealing, the electrical characteristics of the p–n junction diodes, formed by the backside laser doping technique, became optimized and 57Co spectra were almost unchanged. It was supposed that a Schottky barrier at the In/CdTe interface was degraded, while a p–n junction, created in a deeper region of the CdTe crystal, remained functional even after melting and solidifying the In contact.