Temperature-dependent Hall-effect measurements on two Cr-doped GaAs samples
show a dominant center at E1 =0.324—1.4 x 10-4T eV, with respect to the valence-band edge. By comparison with secondary-ion mass spectroscopy measurements of the Cr concentration, and recent EPR measurements of the Cr2+, Cr3+, and Cr4+ concentration in several samples, it is shown unambiguously that this energy describes the Cr4+→Cr3+ transition. This is the first conclusive evidence for a charge-state transition involving Cr4+ in GaAs.
Look, D. C.,
& Eaves, L.
(1982). Positive Identification of the Cr(4+)-->Cr(3+) Thermal Transition in GaAs. Physical Review Letters, 49 (23), 1728-1731.