On the excited and metastable states of cr-related double centres in gaas

The energy levels of a Cr-related trigonal centre in GaAs are studied both experimentally and theoretically. New lines and absorption bands in the energy interval of 0.9 < hv < 1.4 eV are discovered in the p-type GaAs:Cr by the method of light-induced modulation of absorption. These lines are ascribed to the intra-centre transitions with charge transfer at a [Cr-X] trigonal defect, [Cr^-X^-] —->[Cr°X°], where [Cr°X⁰) are metastable vibronic states with a large relaxation time which is found to be 10^-1 s at room temperature. The microscopic theory of such a double defect is developed with the assumption that X is the arsenic vacancy and the strong lattice relaxation is originated from the pseudo-JahnTeller effect due to the tunnelling of an electron between Cr_Ga- and V_As-related deep levels of the double-well effective potential.