Non-Linear Analytical Approach to Investigate Barrier Layer Parameter Effect on 2DEG and DC Characteristics in AlGaN/GaN HEMTs

This paper investigates the DC characteristics of a two-dimensional (2D) analytical model of AlGaN/GaN High Electron Mobility Transistor (HEMT), based on the solution of Poisson’s equation and incorporating the effects of spontaneous (P_S_P) and piezoelectric (P_PZ) polarization. The behaviour of the sheet carrier density (nₛ) is studied using a non-linear model of the Fermi level, and the two-dimensional electron gas (2DEG) current–voltage characteristics incorporate the effects of velocity saturation, field-dependent mobility, and parasitic resistances. Additionally, variations in the threshold voltage (V_th) and nₛ are examined in relation to barrier thickness (d_AlGaN) , aluminum mole fraction (n), and the doping density (N_D) of the barrier layer. In predicting the 2DEG density and V_th with varying n, d_AlGaN and ND, both P_S_P and P_PZ polarization effects were considered. The nₛ increased with d_AlGaN , from 1.3 × 1013 cm–2 at 20 nm to 1.4 × 1013 cm–2 at 34 nm, while V_th shifted negatively from –4.7 to –9.4 V due to reduced gate control at higher thickness. For n, nₛ rose from 1.0 × 1013 to 1.7 × 1013 cm–2 as n increased from 0.20 to 0.30, with V_th moving from –4.0 to –6.2 V, driven by enhanced polarization and carrier confinement. Similarly, increasing N_D from 1 × 1018 to 6 × 1018 cm–3 elevated nₛ from 1.3 × 1013 to 1.4 × 1013 cm–2 and shifted V_th from –4.3 to ‒6.1 V, due to a higher supply of free electrons. The results obtained from this work closely match simulated data, confirming the validity of the model.