Electrical characterization of CuInSe2 crystals

Schottky junctions were fabricated by evaporating Al on Bridgman-grown monocrystalline p-type CuInSe2 substrates. The effect of single crystal surface preparation on the electrical behavior of the devices was studied. Crystals were mechanically polished and then etched in a bromine/methanol solution. In addition, a group of crystals received a 350°C heat treatment in argon.Devices that received the substrate anneal showed a substantial reduction of junction current. Capacitance-voltage measurements performed at different frequencies indicated the presence of a large density of defect states. The frequency dependence of the capacitance was much more pronounced in non-heat treated devices. The substrate anneal can improve the near-surface quality by reducing defect states created by the mechanical polishing/chemical etching step.Deep level transient spectroscopy (DLTS) revealed a majority carrier trap at 0.18 eV above the valence band in both heat-treated and non-heat treated crystals. A clear relationship between the density of this trap and the CuInSe 2 substrate anneal step could not be established. Electron beam induced current (EBIC) measurements revealed that a buried homojunction was not present in the Schottky junctions. The CuInSe2 minority carrier diffusion length as well as the surface recombination velocity of both cleaved and polished CuInSe2 surfaces was measured by EBIC