Some optical properties of Cu in GaP

Measurements of photoquenching (and photostimulation) spectra of luminescence are shown to be useful for studying selectively the spectral dependence of photo-ionization cross-sections of deep level impurity centres. This method is applied to Cu-doped GaP, where all observed IR-induced phenomena could be related to the properties of the red donor-acceptor (Cu) pair emission. From steady-state quenching spectra the spectral dependence of the optical emission rate for holes of the Cu-acceptor was found to be in good agreement with Lucovsky's model. The corresponding threshold energy was found to be EA = (0.51 ± 0.01) eV at low temperatures, and the temperature dependence of EA suggests, that this Cu level might be pinned to the conduction band below 160 K.