Investigation on interface charges in SiN/AlxGa1-xN/GaN heterostructures by analyzing the gate-to-channel capacitance and the drain current behaviors

In SiN/AlGaN/GaN heterostructures, the evaluation of interface charges at the SiN/AlGaN and AlGaN/GaN interfaces is crucial since they both rule the formation of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. In this paper, we conducted a thorough analysis of the gate-to-channel capacitance C-GC(V-G) and of the drain current I-D(V-G) over a gate voltage V-G range enabling the depletion of the 2DEG and the formation of the electron channel at the SiN/AlGaN interface. This work includes the establishment of analytical equations for V T H 1 (formation of the 2DEG) and V T H 2 (formation of the electron channel at the SiN/AlGaN interface) as a function of interface charges and of the p-doping below the 2DEG. The inclusion of the p-doped layer below the 2DEG and the use we made of V T H 2 have not been reported in previous studies. Our analysis allows a reliable estimate of the interface charges at the AlxGa1-xN/GaN and SiN/AlxGa1-xN interfaces for various Al concentrations x as well as to demonstrate that the polarization charge at the SiN/AlxGa1-xN interface is compensated, which confirms previous findings. Moreover, this compensation is found to be induced by the AlGaN layer rather than the SiN layer.