Point defect study from low photoluminescence of the CdIn 2S 4 films grown by hot wall epitaxy method

Abstract

After the CdIn 2S 4 films grown by hot-wall epitaxy method were annealed in Cd-, S- and In-atmospheres, the point defects were investigated by using the low photoluminescence (PL) experiment. In the as-grown CdIn 2S 4 films, the free excitons corresponding to the light hole and the heavy hole have been observed, and their splitting gap was 8.2 meV.The gap is associated with the strain caused by the lattice mismatch between the substrate and the film in the heterojunction growth. By means of thermal annealing in various atmospheres, the (D°,X) emission was observed to originate from the V S or Cd int. From this emission, the E D value of the donor impurity level is extracted to 0.1950 eV.Also, the emission between the free electrons and the acceptor holes (FA) became a dominant peak after S atmosphere treatment, and the E A value of the acceptor level is turned out to be 0.2371 eV.Thus, the origin of the FA emission is related to V Cd or S int. These PL results led us to confirm that CdIn 2S 4:S is converted into the optical p-type. In addition, the origin of the donor–acceptor pair emissions is caused by the recombination between donors such as V S or Cd int and acceptors such as V Cd or S int. Based on these PL results, we have schemed a new energy-level diagram of the recombination process in CdIn 2S 4.