Quantum-confined stark effect and localization of charge carriers in Al$_{0.3}$Ga$_{0.7}$N/Al$_{0.4}$Ga$_{0.6}$N quantum wells with different morphologies

The electric fields in Al$_{0.3}$Ga$_{0.7}$N/Al$_{0.4}$Ga$_{0.6}$N quantum wells are estimated. The quantum wells are grown by plasma-assisted molecular-beam epitaxy with plasma activation of nitrogen. The three-dimensional and planar modes of buffer layer growth are used. The transition to the three-dimensional mode of growth yields a substantial increase in the photoluminescence intensity of the quantum wells and a shift of the photoluminescence line to shorter wavelengths. These effects are attributed to the fact that, because of the extra three-dimensional localization of charge carriers in the quantum-well layer, the quantum-confined Stark effect relaxes. The effect of localization is supposedly due to spontaneous composition fluctuations formed in the AlGaN alloy and enhanced by the three-dimensional growth.