Effects of the spontaneous polarization and piezoelectric fields on the luminescence spectra of GaN/Al0.15Ga0.85N quantum wells

We have investigated the well width dependence of the ground level emission of GaN/AlGaN quantum wells. We find that the fundamental electron–heavy-hole transition red-shifts well below the GaN bulk gap for well widths larger than 3 nm and that the luminescence intensity reduces with increasing well thickness. These effects originate from the quantum confined Stark effect caused by the strong built-in electric field induced by the spontaneous polarization charge at the GaN/AlGaN interfaces and, to a minor extent, by the piezoelectric charge, with typical strength in the MV/cm range. The experimental data are quantitatively explained by means of a self-consistent tight-binding approach which includes screening (either dielectric or by free carriers) and spontaneous polarization field.