Photothermal capacitance measurements on GaP:Ni

Abstract

The photocapacitance spectrum of n-type GaP:Ni shows a peak near 0.74 eV and a rising edge at higher energies. The properties are consistent with the peak being due to photothermal ionisation to the conduction band via the excited state of the d9 configuration, while the rising edge is due to photoionisation directly from the d9 ground state to the conduction band. Experiment and theory agree that the effective capture rate of electrons is the same whether excitation is via the excited state or direct to the conduction band. A previously reported absorption process with threshold energy 0.78 eV is shown to be different from that giving the photocapacitance spectrum, and it is explained how one centre may dominate the absorption spectrum and a different one dominate the photocapacitance spectrum.