Nickel, a persistent inadvertent contaminant in device-grade vapour epitaxially grown gallium phosphide

The presence of Ni in vapour-phase epitaxy (VPE) GaP has been detected through the strong photoluminescence band it induces in the infrared, centred near 2 mu m. The band remains intense up to <or approximately=130K, but is quenched to approximately 5% relative intensity at 300K. It shows appreciable structure at low temperature, with no-phonon transitions near 0.66 eV and prominent coupling to a well-defined gap mode of 41.3 emV. This luminescence apparently arises from an intra-d-state radiative relaxation process of Ni Ga(d⁸). This luminescence is a persistent feature of undoped VPE GaP and may be present up to 30% of the strength observed in Ni-diffused material.