Radiative Pair Transitions in p-Type ZnSe: Cu Crystals

Abstract

Shallow levels with an ionization energy of 0.012 eV play an important role in the photoelectronic properties of p-type ZnSe:Cu crystals. These levels exhibit the characteristics of the higher-lying member of an imperfection pair involved in luminescence emission, as well as of a trap determining long-time decay rates of luminescence and photoconductivity, and of a center causing low-temperature reduction of free-electron lifetime. The participation of the shallow level in low-temperature pair emission is demonstrated by the thermal quenching of the emission at 50°K with an activation energy of 0.012 eV, whereas the acceptor forming the lower-lying member of the pair lies 0.72 eV above the valence band, and by the shift in the position of the emission band below 50°K with changing excitation intensity. The energetics of the emission and the 10−20 cm2 electron cross section determined from decay suggest that the shallow level may be an acceptor rather than a donor.