Radiative recombination in melt-grown and Cd-implanted CuInSe2

Abstract

The behavior of the low‐temperature emission spectra of melt‐grown p‐type and Cd‐implanted n‐type CuInSe2 with changes in temperature and excitation intensity have been investigated. Broad‐band emission was dominant in the melt‐grown crystals grown under an excess Se atmosphere. Generally, the broad‐band peak was observed to occur at ∼0.94–0.95 eV, all peaks lying in the broad range of energy of ∼0.87–0.95 eV at 4.2 °K. The band was observed to shift to higher energy as the excitation intensity or temperature was increased, which implies that the band is due to a donor‐acceptor pair mechanism. The spectral characteristics are explained by the presence of an acceptor level (E A =85±2 meV) and a donor level (E D =65±2 meV) and by compensation‐dependent band shift in the p‐type crystals. Acceptors and donors responsible for the pair band appear to be Cu and Se vacancies. The change in the peak energy of the band per decade of excitation intensity was found to be in the range 4–25 meV at 4.2 °K. The shift of the broad‐band peak to lower energies and the increase in the magnitude of the energy shift due to the excitation intensity are consistent with high doping and compensation. A broad emission band was also observed in Cd‐implanted crystals at low temperatures. The temperature dependence of the broad band in these crystals was opposite to that of the p‐type crystals, the peak shifting to lower energy with an increase in temperature.