Electric dipole spin resonance methods revealed 2 trigonal triplet spectra and a number of almost isotropic lines at 24, 33 and 60GHz in samples of dislocation-free material which had been doped with Zn by diffusion. The absolute and relative strengths of the lines varied with the diffusion parameters, background doping of the samples and post-diffusion annealing treatment. Illumination with white light led to a metastable change in the relative heights of the spectra. None of the above spectra were observed in dislocation-rich samples. Instead, a broad background was observed after illumination; with a sequence of 1 dispersion-like and 3 absorption-like anisotropic absorption structures that were periodic in B, plus a further isotropic dispersion-like line.

H.Schroth, R.App, A.Köpf, K.Lassmann, H.Bracht, N.A.Stolwijk: Materials Science Forum, 1995, 196-201, 1601-6