The strong APR spectrum from trigonal Cr2+in GaAs

The authors report a study of the intense acoustic paramagnetic resonance spectra observed in semi-insulating or illuminated n-type chromium-doped gallium arsenide. The experimental data are compared with a Jahn-Teller model for Cr 2- ions occupying substitutional sites but subject to a large trigonal distortion as well as to random lattice strains (Cr 2 -II). Despite the lack of a detailed knowledge of this lattice strain distribution, a satisfactory fit to the major experimental features is obtained after noting that the four equivalent directions for the trigonal strain are not magnetically equivalent for an arbitrary magnetic field direction. The origin of this large trigonal distortion present at a small fraction of the Cr sites is, however, unexplained.