Luminescence in III-nitrides

A collection of photoluminescence (PL) data for GaN as well as AlGaN/GaN and InGaN/GaN quantum structures is presented and discussed. We focus first on characteristic PL spectra for donors and acceptors in GaN, where several PL spectra are observed, but unfortunately so far not safely identified with any specific donor or acceptor. An interesting infrared PL spectrum in electron-irradiated GaN seems to be O-related, in close similarity to the so called electron capture emission for the substitutional deep OP donor in GaP. The modulation doped AlGaN/GaN heterostructures and quantum wells show some PL emission related to the two-dimensional electron gas, but the potential fluctuations in these systems are still quite large, which affects the quality of the data. The InGaN/GaN quantum well (QW) structures finally show a very broad PL emission downshifted by a large fraction of an eV from the expected unperturbed QW bandgap, illustrating the action of the piezoelectric field but also the presence of strong potential fluctuations. These broad emissions do not show any direct sign of excitonic origin, rather we argue they are largely due to recombination of separately localised electron-hole pairs.