Effects of a GaN cap layer on admittance characteristics of AlGaN/GaN MIS structures

GaN caps are commonly used to reduce sheet charge modulation induced by AlGaN/GaN surface potential. However, the details on how GaN caps affect C- V and G- V characteristics are still unclear. In this paper, we report a difference between these characteristics with and without GaN caps, and we discovered a mechanism in which GaN caps act as quantum wells to affect the charging and discharging of interface states. Finally, we developed a numerical model to simulate admittance characteristics of AlGaN/GaN MIS structures with a GaN cap in high accuracy.