Fermi level pinning at CdS/Cu(In,Ga)(Se,S) 2 interfaces: effect of chalcopyrite alloy composition

• Published in: The Journal of physics and chemistry of solids Vol. 64; no. 9; pp. 1591 - 1595
• Main Authors: Turcu, M., Rau, U.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2003; Elsevier
• Subjects: A. Chalcogenides; A. Interfaces; A. Thin films; Condensed matter: electronic structure, electrical, magnetic, and optical properties; D. Transport properties; Electrical properties of specific thin films; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Other inorganic semiconductors; Physics; A. Thin films; D. Transport properties; A. Interfaces; A. Chalcogenides; Valence bands; Inorganic compounds; Indium selenides; Cadmium sulfides; Energy gap; Charge carrier recombination; Band theory; Chemical composition; IV characteristic; Band structure; Interface energy; Digital simulation; Transition element compounds; Theoretical study; Zinc oxides; Chalcopyrite; Fermi level; II-VI semiconductors; Copper sulfides; Alloying; Heterostructures
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/S0022-3697(03)00137-9

We introduce a quantitative model for the band diagram of ZnO/CdS/Cu(In,Ga)(Se,S) 2 heterostructures and for carrier recombination at the CdS/chalcopyrite interface. We derive analytical expressions for the open circuit voltage and the Fermi energy position at the active interface. The open circuit voltage under interface recombination is almost independent from the band gap energy of the chalcopyrite when the valence band edge of the absorber remains at the same energy position. The analytical calculations are in relatively good agreement with numerical simulations. Experimental current–voltage analysis indicates that devices prepared from Cu-poor Cu(In,Ga)(Se,S) 2 chalcopyrites are dominated by recombination in the bulk of the absorber while interface recombination prevails if the absorbers are prepared under Cu-excess. In the latter case, the experimentally determined interface barriers reveal that the interface Fermi energy position shifts upward on the energy scale upon increasing the Ga content into the absorber and remains at a relatively low energy value under S/Se alloying.