Optical investigations of the states in GaP:Ni

Abstract

This paper reports photoconductivity measurements of semi-insulating Ni-doped GaP materials. The photoresponse spectra obtained exhibit strong onsets at 0.62 eV and 0.95 eV, as well as a number of weaker features. Optical transitions are interpreted as between Ni3+ and Ni2+ ions, and the conduction and valence bands, as well as transitions involving a nickel-related defect. An energy diagram (at 300K) is deduced to consist of an Ni2+ ground state at 0.62 eV above the valence band and three excited states, and a nickel-related level located at 0.95 eV above the valence band. Optical absorption measurements have shown that the Ni+ two-electron trap concentration is negligible in semi-insulating GaP materials and increases appreciably under white light illumination.