Analytically Modeling the Effect of Buffer Charge on the 2DEG Density in AlGaN/GaN HEMT

In this article, an analytical model of the buffer charge (BC) effect is presented for the 2-D electron-gas (2DEG) density (n(S)) prediction in AlGaN/GaN high-electron-mobility-transistor (HEMT). Through applying Gauss' Law, the buffer doping concentration (N-bu) and energy level (E-bu) dependent BC density (sigma(BC)) is analytically expressed. Then, the contributions of the sigma(BC) on the n(S) are included in the n(S) calculation. We propose and utilize the one-variable quadratic equation method to analytically express the sigma(BC) according to the understanding of AlGaN/GaN device semiconductor physics. Substituting the obtained sigma(BC), we establish the quantitative analytical relationship between the n(S) and the N-bu under different E-bu cases, which enhances the n(S) prediction model of the AlGaN/GaN HEMT. Compared to the conventional method without considering the BC effect, the established analytical model better predicts the n(S)-N-bu curves with the various E-bu and is in good agreement with the experimental data. Verified by the simulation and experiment, the proposed analytical model serves as beneficial guidance for the epitaxial structure design, leakage (or breakdown) and dynamic ON-resistance performance investigation, and device or circuit simulation model implementation for AlGaN/GaN HEMT.