Pressure-dependent measurements on n⁺GaAs (Si, Sn): the effect of deep donor (DX) states on the electrical properties and persistent photoconductivity

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Shubnikov-de Haas and persistent photoconductivity measurements are used to study the mobility, free electron density (n) and the occupancy of the DX centre in heavily doped n-GaAs as a function of doping level and hydrostatic pressure. The results show that the DX centre produces a resonant donor level between the Γ - and L-conduction band minima at a concentration comparable with the doping level. For the Si-doped samples, comparison with local vibration mode measurements indicates that the DX level can be identified with SiGa. The level acts to pin the Fermi energy at electron concentrations around 1.8 × 1019 cm−3. Analysis of the results indicates that macroscopic charge separation is not responsible for persistent photoconductivity in these samples.