Pair Spectra Involving Donor and/or Acceptor Germanium in GaP

Abstract

Photoluminescence spectra were obtained between 20° and 298°K for GaP crystals containing germanium alone or in combination with shallow acceptors (zinc or cadmium), or shallow donors (tellurium or selenium), or a deep donor (oxygen). Emission bands at 77°K at 1.942, 1.907, 1.823, 1.815, 1.38, and 1.59 eV were correlated, respectively, with the simultaneous presence of both germanium and zinc, germanium and cadmium, germanium and tellurium, germanium and selenium, germanium and oxygen, and germanium alone. The shift between the zinc‐germanium and the cadmium‐germanium bands was just the difference in binding energies between the two shallow acceptors, indicating that the emission was due to donor‐acceptor recombination between the shallow acceptor and a deep germanium donor level of binding energy ≤0.36 eV. Similarly the shift between the tellurium‐germanium and selenium‐germanium bands indicated pair recombination between the shallow donor and a deep germanium acceptor of binding energy ≤0.45 eV. The band associated with germanium alone corresponded to a pair band involving both donor and acceptor germanium, the maximum in the emission corresponding to a much smaller donor‐acceptor separation (18 Å) than for the bands involving shallow levels (52 Å) because the carriers are more tightly bound in the former case. The band at 1.38 eV was ascribed to a pair band between oxygen donors and germanium acceptors. Thermal quenching of the emission bands was predominantly due to thermal release of minority carriers after (efficient) capture by the ionized deeper level of the pair in the compensated samples.