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

Abstract

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 ${\mathrm{GaN/In}}_{\text{0.18}}{\mathrm{Ga}}_{\text{0.82}}\mathrm{N/GaN}$ 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 $\text{0.6±0.2\hspace{0.17em}}\mathrm{V}$ across, and an internal electric field of $\text{−2.2±0.6\hspace{0.17em}}\mathrm{MV/cm}$ 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 ${\text{8×10}}^{20}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}},$ corresponding to a sheet charge density of $\text{0.027\hspace{0.17em}}{\mathrm{C/m}}^2.$ Free electron and hole densities of the order of ${10}^{20}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ are confined separately in the quantum well. These free carriers screen only part of the electric field due to the polarization effect.