Evidence for Radiative Recombination between Deep Donor-Acceptor Pairs in GaP at Room Temperature

Abstract

Radiative donor‐acceptor pair recombination between the deep‐donor oxygen and a shallow acceptor (zinc or cadmium) in p‐type crystals remains a dominant radiative recombination process in GaP at room temperature as it is at low temperatures. This mechanism is deduced from the spectral shift when one shallow acceptor is replaced by another, and from the dependence of photoluminescence intensities upon the simultaneous presence of both oxygen and the acceptor (zinc or cadmium). The minority carrier electron captured by the ionized donor is not readily released back to the conduction band thermally because the donor is quite deep. The thermal population of holes on the shallow acceptors is quite large even at room temperature, so that the trapped electrons can recombine with these holes. No radiative transitions between free holes and the trapped electrons are observed, implying that the capture cross section of a neutral oxygen donor for a free hole is −19 cm². Since the widths of the pair bands involving oxygen are greater than the difference in binding energies between zinc and cadmium, the two bands overlap in crystals containing oxygen and both acceptors. The sum band exhibits no structure but its position depends on the zinc‐to‐cadmium ratio.