Photoluminescence study of heat-treated InP

Low-temperature photoluminescence is used to study optical transitions in InP which arise from moderate-temperature annealing or dielectric encapsulation. A total of seven shallow emission lines appear in annealed or encapsulated InP that are not present in unprocessed material. These transitions are easily observed in undoped substrates. They are less intense or absent in Fe-doped material, and are not seen in p-type material. It is found that dielectric capping with SiO2 enhances the formation of several transitions, while phosphosilicate glass or Si3N4 effectively suppresses their formation. Surprisingly, some of these recombination centers are found to extend many microns into the substrate after SiO2 deposition at 350 °C or after annealing at temperatures as low as ∼400 °C. These centers appear to be related to previously observed processing-induced carrier concentration changes. Possible origins of the transitions are discussed.