Hall and photo-Hall effect measurements on sulphur-doped GaSb
In this work bulk sulphur-doped (ND>1017 cm-3) GaSb crystals have been investigated by performing Hall and photo-Hall measurements at different intensities of subgap illumination in the temperature range 14-300 K. At low temperature (T<100 K) a persistent photoconductivity (PPC) effect, similar to that observed for the DX centre in AlxGa1-xAs, has been found. Low-temperature conductivity exhibits the light-induced Mott transition, indicating the existence of sulphur-related shallow states linked to the Gamma minimum. In contrast to AlxGa1-xAs, the low-temperature saturated PPC electron concentration ( approximately 4*1015 cm-3) is much smaller than that expected from high-temperature measurements. Starting from the PPC condition, transient Hall measurements in the temperature range 80-100 K, where thermally activated electron capture is observed, have revealed a quenching of the photosensitivity, which depends on the total number of incident photons. On this basis a phenomenological model of the deep donors in GaSb:S is proposed, invoking the existence of two sulphur-related deep states with different photosensitivity and thermally activated capture cross section. Hall data are also supported by low-temperature capacitance-voltage measurements performed in the dark and after white-light illumination.