Effects of chemical and electrochemical etching on polycrystalline thin films of CuGaSe₂

Electrochemical and, especially, chemical oxidative etching drastically improves the photoresponse of liquid electrolyte/CuGaSe₂-on-Mo junctions. This is expressed in decreased effective doping levels and increased effective minority carrier diffusion lengths. It is accounted for by removal of highly defective surface layers, which also leads to an increase in the barrier height, as judged from a positive shift of the flat band potential (on the electrochemical scale). The etching effects are seen clearly in Zn/CuGaSe₂ devices, by electron beam-induced current. This last method also reveals a supra-grain structure, which is tentatively explained by thermal stress-induced strain at the Mo-CuGaSe₂ interface.