Bistable defect systems in (M = Al, Ga, In) and their photorefractive properties

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Abstract
On the basis of the method recently used in the study of the trivalent impurity state in (M: In, Ga, Sc and Y), the structure of the electron trapped at an centre in is determined. Although a bistable system is obtained, due to the locally soft lattice around the ion the localized compact state has higher energy than the delocalized state. The excited p-like states and the oscillator strengths for the optical transition between the s- and p-like states in the three bistable systems (with Al, Ga, In) are evaluated. The changes in the refractive index as the systems change from localized to delocalized states are estimated, and the results are discussed in the context of the recently reported data on the photorefractive properties of In and Ga centres in .