Modeling and Analysis of Terminal Capacitances in High-Power Devices: Application to p-GaN Gate HEMTs

Experimental data from gallium nitride (GaN)-on-Si p-GaN gate high-electron-mobility transistors (HEMTs) reveal a strong dependence of terminal capacitances-particularly $C_{\mathrm{BS}}, C_{\mathrm{BG}}$ , and $C_{\mathrm{BD}}$ -on the drain-to-source voltage ( $V_{\mathrm{DS}}$ ), indicating significant coupling through the bulk contact. This behavior, linked to progressive depletion of the 2-D electron gas (2DEG) under field plates, is not adequately captured by existing compact models. This work presents a detailed analysis of the dynamics of $V_{\text {DS }}$ -dependent depletion under field plates and develops an enhanced MIT Virtual Source GaN FET (MVSG) compact model that incorporates bulk-related capacitance contributions. The proposed model introduces a depletion-dependent modulation of channel and fringing capacitances and captures channel length modulation (CLM) effects due to progressive depletion of 2DEG with increasing $V_{\text {DS }}$ . The extended model shows excellent agreement with the measured capacitance behavior and provides a deeper understanding of the substrate interaction mechanisms. This advancement supports the design of next-generation high-voltage GaN power ICs, such as integrated half-bridges and gate drivers, by enabling accurate prediction of terminal capacitances in simulations that include substrate effects.