DX CENTER CHARACTERIZATION IN SE-DOPED ALGAAS UNDER HYDROSTATIC-PRESSURE

Se-related DX centres in AlGaAs alloys have been characterized by deep-level transient spectroscopy techniques under hydrostatic pressure. The thermal-emission energy, E(e) = 0.24 +/- 0.02 eV, is constant throughout the alloy range considered (0.29 < x < 0.77), and independent of the applied pressure. The thermal-capture barrier energy follows a V-shaped curve as a function of the alloy composition, with E(cmin) = 0. 13 eV for Al compositions around 38 %, where the Se-DX centre electron occupancy is a maximum. Emission spectra show.up to three peaks generated by three discrete emission rates. Their pressure dependence suggests the existence of three close discrete DX levels originating from changes of the donor local environment. These results confirm the model proposed by Chadi and Chang for Se-related DX centres (group-VI donors). As compared with the Si-DX centre properties quantitative differences originate from a shallower energy position of Se-DX centres in the gap, owing to smaller values of the thermal emission and capture barriers, 200 meV and 70 meV lower, respectively.