Annealing studies on CuIn(Ga)Se-2: the influence of gallium

In-rich CuInSe2 (CIS) and CuIn(Ga)Se-2 (CIGS) with Ga/(Ga+In) = 28% were an nealed in air at 400 degrees C. After annealing the Ga-free CIS layer, the broad photoluminescence (PL) spectrum changes to a structured spectrum whic h is identical to that of a Cu-rich layer. Annealing of In-rich films cause s the passivation of donors and the reduction of the high compensation. The change in the PL spectrum and the clear reduction of compensation cannot b e seen for the Ga-containing CIGS layers. Only a slight blue shift of the s pectrum and an increase of the Cull width at half maximum is observed after air annealing. However, photoluminescence excitation experiments reveal a decrease of the band-tail character of the absorption edge which can be int erpreted as a decrease in compensation. Air-annealing causes a strong reduc tion of the Ga-concentration in the CIGS layer. The Ga-loss can be detected by X-ray diffraction and secondary ion mass spectroscopy. Ga segregates as oxide phase on top of the crystal and is analysed with X-ray photoelectron spectroscopy. The thickness of that oxide layer was estimated to be 100 nm . (C) 2000 Elsevier Science S.A. All rights reserved.