Charge transfer ${\mathrm{Cr}}^{3+}\left({3d}^3\right)\to {\mathrm{Cr}}^{2+}\left({3d}^4\right)$ in chromium-doped GaAs

Results on the absorption and electron paramagnetic resonance measurements on chromium-doped GaAs are reported. For $p$-type samples the main optical transitions are shown to be due to a photoionization process which has been measured as a function of temperature and hydrostatic pressure. A model, developed in the configurational diagram scheme and using two types of relaxation, is proposed to explain the experimental results.