Electronic properties of intimate Mo and CdS junctions in-situ formed on CuInSe2 (011) cleavage planes

Clean CuInSe₂ (011) surfaces are prepared in UHV by cleavage of single crystals. The structural and electronic properties of the cleavage planes and of the intimate heterocontacts to Mo and CdS are investigated by electron diffraction (LEED) and photoelectron spectroscopy (UPS, (S)XPS). The cleavage planes are stoichiometric and close to flatband conditions. Ion bombardment and annealing leads to structural disorder, changes in surface stoichiometry, and to band bending. The intimate p-CuInSe₂ (011)/Mo contacts is reactive and interfacial metallic In is formed. A Schottky type contact with a barrier height of about 0.8 eV is established. Deposited CdS forms a non-reactive overlayer at room temperature. The experimentally determined valence band and conduction band offsets are 0.8 and 0.7 eV, respectively, in deviation from the electron affinity rule. At sample temperatures above 490 K a Cu_xS interfacial reaction layer is formed and the valence band offset is reduced to 0.3 eV. The intimate heterocontacts investigated here do not correspond to the common knowledge of CuInSe₂ solar cells suggesting more complex interface processes there