Pb0.8Sn0.2Te Infrared photodiodes by indium implantation

Indium ions were implanted in p-type Pb0.8Sn0.2Te films to produce shallow p-n-junction infrared photodetectors. The films were grown epitaxially on BaF2 (111) cleavage planes and showed hole concentrations of the order of 10 17 cm-3. The indium implantation was carried out using doses between 2 x 1013 and 1 x 10-15 cm-2 and an energy of 700 keV with the films either at room temperature or 450 K. The indium concentration profiles were determined by SIMS before and after annealing of the implanted films at temperatures up to 670 K. The implanted films were covered with silicon nitride layers to avoid evaporation during the subsequent annealing. The electrical properties caused by the indium implantation were examined by far infrared reflectivity measurements in the plasma resonance region. The carrier type of the implanted layers was determined by a conventional thermoelectric method. To convert the implanted layers into n-type the films had to be annealed at a temperature of at least 570 K for 30 min. regardless of the implanted indium dose. Mesa diode were fabricated by standard photolithographic procedures. Zero bias resistance area products as high as 0.4 Ω cm2 were obtained