Two-dimensional electron gas density in high Al content AlxGa1-xN/GaN double heterostructure

Al content in Al_xGa_1-xN/GaN double heterostructure (DH) is improved high up to x=1 by using a compressively strained GaN quantum well (QW) layer. By solving the coupled Schrodinger and Poisson equations self-consistently, we investigate the two-dimensional electron gas (2DEG) distributions and sheet densities in Al_xGa_1-xN/GaN DHs. Comparing to the 2DEG in Al_0.5Ga_0.5N/GaN single heterostructure (SH), the 2DEG sheet density in a comparable AlN/GaN/Al_0.5Ga_0.5N DH is nearly doubled from 2.31×10¹³cm^-3 to 4.47 × 10¹³cm^-3, mainly owing to the additional piezoelectric polarization in the GaN QW. It is also shown that 2DEG in the GaN QW is increased with increasing the Al content of the top barrier due to the stronger polarization effect and large conduction band offset at the Al,Ga_1-xN/GaN interface. Increasing the lower barrier thickness will reduce the 2DEG density in the GaN QW while the 2DEG at the lower Al_yGa_1-yN/GaN interface is increased, making the total 2DEG density almost a constant.