Irradiation-Produced Band-Tailing in Semiconductors

Band-tailing produced by electron irradiation at room temperature has been studied in various semiconductor materials using infrared absorption. The bandtailing can be produced by both 30- and 1-MeV electrons. GaAs is quite sensitive to the production of band-tailing, and InSb and Si show a lesser effect. PbTe and Ge show no band-tailing produced by these irradiations, but this is more likely due to the annealing of the necessary defects at this relatively high temperature than to any inherent material insensitivity. The annealing of the band-tailing has been studied and is found to occur primarily in several well defined stages. These stages can often be correlated with the annealing stages of isolated defects. Photoconductivity results show that the band-tailing is an absorption phenomenon. This result agrees with previous calorimetric measurements. A hypothesis involving absorption at states produced by disorder in the crystal near the band edge is put forward to explain the various aspects of band-tailing.