Identification of the BiGa heteroantisite defect in GaAs:Bi

GaAS lightly doped with the heaviest group-V atom, bismuth (Bi), has been studied by conventional electron-spin resonance (ESR) and by ESR detected via the magnetic-circular-dichroism (MCD) absorption. A new Bi-related sharp-line MCD band has been observed on which two MCD-ESR lines have been discovered. They are shown to arise from the singly ionized BiGa double donor. Most remarkably, a substantial fraction, about 10 percent, of the total Bi content is found to occupy the Ga site. The BiGa MCD absorption band is tentatively assigned to an exciton deeply bound to the singly ionized double donor BiGa+.