Electrical properties of SiN<i>y</i>/Al1−<i>x</i>Sc<i>x</i>N/GaN-based metal–insulator–semiconductor structures

The electrical properties of SiNy/Al1−xScxN/GaN-based metal–insulator–semiconductor (MIS) structures, including electron sheet density, electron mobility, depletion behavior, and off-state leakage current, were systematically investigated as a function of Sc concentration (x = 0.06–0.17). A reduction in polarization-induced charge with increasing Sc concentration was observed, evidenced by lower electric fields needed to deplete the two-dimensional electron gas (2DEG) confined close to the Al1−xScxN/GaN interface and the corresponding decreases in electron sheet density from 2.5 × 1013 to 2.0 × 1013 cm−2. These measured values are at least two times lower than theoretical predictions, likely due to expected high carbon and oxygen impurity levels in the grown barrier layers. A pinch-off instability was found to occur after SiNy passivation removal. The electron mobility was found to be inversely correlated with Sc concentration declining from 950 to almost 750 cm2/Vs, attributed to interactions between the 2DEG and the barrier. Furthermore, the off-state leakage current investigations revealed a minimum in leakage current at x = 0.12. Accordingly, an optimal Sc concentration range between x = 0.10 and 0.12 was identified that balances depletion behavior, mobility, electron sheet density, and leakage current, potentially due to near lattice-matched conditions between Al1−xScxN barrier and GaN-channel layer. These findings provide crucial insights for the development of high-performance Al1−xScxN/GaN-based transistors for next-generation high-frequency and high-power electronic applications.