Impact of epitaxial structural parameters on two-dimensional hole gas properties in p-GaN/AlGaN/GaN heterostructures

Research on p-channel field-effect transistors (p-FETs) remains limited, primarily due to the significantly lower conductivity of the two-dimensional hole gas (2DHG) compared to the two-dimensional electron gas (2DEG) in n-channel field-effect transistors (n-FETs), which poses a significant challenge for monolithic integration. In this study, we investigate the impact of epitaxial structure parameters on 2DHG properties in p-GaN/AlGaN/GaN heterostructures through semiconductor technology computer-aided design (TCAD) simulations and theoretical calculations, identifying the conditions necessary to achieve high-density 2DHG. Our simulations demonstrate that increasing the p-GaN thickness leads to two critical thicknesses determined by surface states and acceptor ionization concentration: one corresponds to the onset of 2DHG formation, and the other to its saturation. Lowering the donor surface state energy level and increasing the acceptor ionization concentration promote 2DHG formation and saturation, although the saturated density remains independent of surface states. Additionally, a higher Al composition enhances intrinsic ionization due to stronger polarization effects, thereby increasing the 2DHG sheet density. Consequently, to achieve high-density 2DHG in p-GaN/AlGaN/GaN heterostructures, it is essential to increase the Al composition, ensure that the p-GaN thickness exceeds the critical thickness for 2DHG saturation, and maximize the acceptor ionization concentration. This study elucidates the impact of epitaxial structure parameters on 2DHG properties in p-GaN/AlGaN/GaN heterostructures and provides valuable guidance for the optimization of p-FET designs.