Chemical structures of the Cu(In,Ga)Se2/Mo and Cu(In,Ga)(S,Se)2/Mo interfaces

Using a suitable lift-off technique, we have investigated the chemical properties of the interface between Mo and chalcopyrite compound semiconductors by x-ray photoelectron spectroscopy and x-ray excited Auger-electron spectroscopy. By a systematic comparison of interfaces between S-free [Cu(In,Ga)Se(2) (CIGSe)] as well as S-containing [Cu(In,Ga)(S,Se)(2) (CIGSSe)] chalcopyrites and Mo, we find that the chemical structure at the CIG(S)Se/Mo interface is strongly influenced by the presence or absence of S. We observe an interfacial MoSe(2) [Mo(S(Z)Se(1-Z))(2)] layer formed between CIGSe [CIGSSe] and the Mo layer. The Mo(S(Z)Se(1-Z))(2) layer appears significantly thinner than the MoSe(2) layer and exhibits a different S / (S + Se) ratio [Z=0.9(1)] than the CIGSSe back side [0.5(7)], giving insight into the competition between S and Se during contact formation. Furthermore, we find a significant Ga accumulation at the Mo back contact, which points to pronounced chemical interactions during the formation of the CIG(S)Se/Mo interface.