DX centers in n-type GaAs under hydrostatic pressure

Abstract Raman scattering experiments performed on GaAs:Si as a function of hydrostatic pressure in the indirect-gap range 4–9 GPa, reveal the bistable character of the related impurity level under optical illumination. A numerical simulation of our results shows that the negative U model of Chadi and Chang is valid for reproducing the experimental data at low pressure. However, at very high pressure a positive U description which includes small lattice relaxation is necessary. This demonstrates that the DX defect evolves under pressure, and that a transition from negative to positive U occurs at about 5–6 GPa.