The effect of exciton localization on the optical and electrical properties of undoped and Si-doped AlxGa1−xN

Abstract

The properties of undoped and Si-doped AlxGa1−xN layers grown by metalorganic vapour-phase epitaxy have been investigated by photoluminescence and Hall effect measurements. The variable temperature photoluminescence properties of the layers were typical of AlxGa1−xN, with the temperature dependence of the peak energy showing the often-observed S-shape. The low and variable temperature photoluminescence properties of undoped material could be well described using alloy potential fluctuation theory. However, this was not the case for moderately Si-doped material, for which much larger S-shape behaviour, and thus larger exciton localization, was observed for samples with x > 0.3. The temperature dependence of the PL peak intensity of the Si-doped AlxGa1−xN layers, as well as their Hall activation energies, were then studied in order to obtain possible origins for the large increase in the exciton localization energy. It is tentatively proposed that the increase in the exciton localization could be related to the Γ9 → Γ7 valence band crossover, which occurs at roughly the same composition (0.2 < x < 0.3).