Photoluminescence properties of sodium incorporated in CuInSe2 thin films

CuInSe2 films with Cu/In ratios of m = 0.83-0.99 have been deposited on gla ss substrates by the co-evaporation method using a bi-layer process. The ef fects of sodium in these films have been investigated by comparing the elec trical and optical properties of the films with and without the Na2Se incor poration. Two donor-acceptor pair emissions, [D, A](alpha) at 0.89-0.94 eV and [D, A](beta) at 0.84-0.87 eV, were typically observed in the photolumin escence spectra. The relative intensity of [D, A](alpha) to [D, A](beta) wa s found to depend strongly on both the Cu/In ratio and Na incorporation. Fo r the films with m = 0.94, [D, A](alpha) was predominantly observed regardl ess of Na incorporation. For m less than or equal to 0.9, [D,A](beta) becam e dominant for the films without Na, while [D, A](alpha) remained as the do minant emission for the films with Na. A correlation between the prominence of [D, A](alpha) and resistivities below 2 x 10(3) Omega . cm was found, s uggesting a reduced compensation by suppressed Se vacancy donors due to the presence of Na.