Annealing studies on CuIn(Ga)Se2:: the influence of gallium

In-rich CuInSe2 (CIS) and CuIn(Ga)Se-2 (CIGS) with Ga/(Ga+In) = 28% were annealed in air at 400 degrees C. After annealing the Ga-free CIS layer, the broad photoluminescence (PL) spectrum changes to a structured spectrum which is identical to that of a Cu-rich layer. Annealing of In-rich films causes the passivation of donors and the reduction of the high compensation. The change in the PL spectrum and the clear reduction of compensation cannot be seen for the Ga-containing CIGS layers. Only a slight blue shift of the spectrum 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 interpreted as a decrease in compensation. Air-annealing causes a strong reduction 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.