Study of charge distribution across interfaces in GaN/InGaN/GaN single quantum wells using electron holography

Strong internal electric fields (of the order of MV/cm) influence the electronic properties and light emission process of InGaN quantum wells. We have used electron holography to directly profile the potential and charge distribution across a GaN/In0.18Ga0.82N/GaN quantum well structure, and present here an analysis of the fine-scale potential variations at the quantum well. The potential profiles show a drop of 0.6±0.2 V across, and an internal electric field of −2.2±0.6 MV/cm in the quantum well. An analysis based on Poisson’s equation suggests that the field is caused by electronic charges with a peak density of 8×1020 cm−3, corresponding to a sheet charge density of 0.027 C/m2. Free electron and hole densities of the order of 1020 cm−3 are confined separately in the quantum well. These free carriers screen only part of the electric field due to the polarization effect.