EFFECTS OF ANNEALING ON CUINSE2 FILMS GROWN BY MOLECULAR-BEAM EPITAXY

CuInSe2 (CIS) thin films with a range of Cu/In ratios were grown by mo lecular beam epitaxy on GaAs (0 0 1) at substrate temperatures of T-s = 450-500 degrees C and the effects of annealing under various atmosph eres have been investigated. Photoluminescence spectra obtained from a n ex-situ vacuum annealed CIS film at a temperature of T-A = 350 degre es C showed a red-shift and a broadening of an emission peak (peak c) which originally appeared at 0.970 eV before annealing and the red-shi fted peak c was found to consist of two overlapping peaks. The excitat ion power dependence of these overlapping peaks indicated the radiativ e recombination processes associated with the emissions to be a conduc tion band to acceptor transition (peak at 0.970 eV) and a transition d ue to donor-acceptor pairs (peak at 0.959 eV), indicating the formatio n of a shallow donor-type defect during the vacuum annealing process. The origin of this defect has tentatively been attributed to Se vacanc ies. On the other hand, the molar fraction of oxygen increased with in creasing annealing temperature in dry-air. An epitaxially grown In2O3 phase was found both in Cu-rich and In-rich films annealed at T-A grea ter than or equal to 3.50 degrees C, which was not observed in the fil ms annealed in Ar atmosphere. Thermodynamic calculations based on the Cu-In-Se-O-N system showed In(2)O(3)2 to be the most stable phase in g ood agreement with the experimental results.