Thermal- and optical-excitation processes in GaP : Cu

Abstract

The properties of two deep-level centers caused by Cu doping of GaP have been investigated in p+n diodes and photoconductors by photocurrent methods. Spectra of the cross sections for optical transitions from the valence band to the impurity levels are presented. The band-gap energy and the threshold energy of the deeper level (Ev+0.7 eV) show a similar temperature dependence from 85 to 300 K. The possible influence of other impurities on the optical threshold energy of this center is discussed. The absolute magnitude of the optical cross section for excitation from the valence band to this deep level is temperature dependent. Thermal excitation from the valence band to the shallower level (Ev+0.5 eV) is characterized by an activation energy of 0.54 eV, deduced from the temperature dependence of the thermal-emission rate. A value of about 10−13 cm2 is estimated for the thermal hole-capture cross section at 200 K.