Charge-transfer transitions and pseudoacceptor states of iron in gallium phosphide

Abstract

We report transient shallow bound-hole states of the deep ${\mathrm{Fe}}^{3+/2+}$ acceptor level of iron in GaP, which appear close to the photoionization onsets at 0.82 and 1.23 eV. Optical-absorption spectra with improved signal-to-noise ratio and results from photoluminescence excitation show additional lines not reported hitherto. These data require an assignment of absorption lines which were reported recently. As already outlined for InP and GaAs, we discuss all lines as charge-transfer transitions, a model which is based on transient shallow bound-hole states of a pseudoacceptor. We compare the ground state of the shallow bound hole with the ${\mathrm{Fe}}^{2+}$-related deep acceptor in the three semiconductors InP, GaAs, and GaP. The transient shallow acceptor ground state is bound by about 1/20 of the ionization energy of the corresponding deep acceptor state.