Fig. 1. Schematic of GaN HEMT outer fringing capacitances in different state: (a) In the OFF-state; (b) in the ON-state.

Fig. 2. Schematic of normal electric field between the side wall of the gate and the 2DEG.

Fig. 3. (a) Electric field lines after transforming the nonconfocal elliptical system to the confocal system; (b) the confocal system with L_cd = L_d.

Fig. 4. Error in the confocal system with L_cd = L_d.

Fig. 5. C_ofd versus the extended depletion length induced by donor-like surface traps.

Fig. 6. The curve of the density n_s of 2DEG and E_f versus V_g

Fig. 7. The curve of V_dsat versus V_g.

Fig. 8. The curve of C_ofd versus V_ds obtained from the traditional model and the model in this paper.

Fig. 9. The curve ofC_ofd versus V_th(The illustration show the curve of V_th with Al component and doped concentration).

Fig. 10. The curve of C_ofd versus T

Fig. 11. The curve oftemperature sensitivity of C_ofd under different drain bias.