CHARGE-TRANSFER TRANSITIONS AND PSEUDOACCEPTOR STATES OF IRON IN GALLIUM-PHOSPHIDE

We report transient shallow bound-hole states of the deep Fe3+/2+ acceptor levels 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 a new 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 Fe2+-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.