GaN high-electron mobility transistors (HEMTs) based on nitrogen-polar (N-polar) nitride films are promising for high-frequency millimeter-wave applications. However, realizing high-mobility N-polar GaN/AlGaN heterostructures by metal-organic chemical vapor deposition (MOCVD) remains challenging. In this work, N-polar GaN/AlGaN heterostructures are grown on SiC substrates by MOCVD. By lowering the growth temperature of the high-resistance GaN (HR-GaN) template layer, the two-dimensional electron gas (2DEG) mobility is significantly increased to 1947 cm2/V s, the highest value reported for N-polar GaN/AlGaN heterostructures on SiC. The mobility enhancement is primarily attributed to the effective reduction of oxygen impurity concentration in N-polar heterostructures at lower growth temperature of HR-GaN, leading to weakened ionized impurity scattering toward 2DEG. Importantly, reducing the growth temperature of HR-GaN also substantially increases its sheet resistance, which not only suppresses leakage current of N-polar HEMTs, but also contributes partially to the 2DEG mobility enhancement. This work presents an effective approach for enhancing the mobility of N-polar heterostructures, which is beneficial for the development of high-performance millimeter-wave N-polar GaN HEMT devices.
Ma et al. (Mon,) studied this question.