The role of various scattering mechanisms on electron velocity in Al0.21Ga0.79N/GaN HEMTs

In the present study, the mobility corresponding to various scattering mechanisms under low-field conditions was calculated. Among all scattering mechanisms, polarization Coulomb field (PCF) and polar optical phonon (POP) scattering exhibited the highest mean momentum relaxation rates under low-field conditions. Sentaurus technology computer-aided design (TCAD) coupled Monte Carlo (MC) simulations were employed to calculate the electron drift velocity (ve) of AlGaN/GaN HEMTs under high-field conditions. Individual scattering mechanisms were removed sequentially in the MC framework. The impact of each mechanism on ve under high-field conditions was quantified. The results reveal that under high-field conditions, PCF scattering can reduce ve of AlGaN/GaN HEMTs by 20%–30%. Meanwhile, a method based on the mean momentum relaxation rate was proposed. It can be used to approximate scattering strength and to rank the contributions of different mechanisms in the MC simulations. The highest mean momentum relaxation rate was also obtained for PCF and POP scattering. PCF and POP scattering are, therefore, identified as the dominant carrier-scattering mechanism in AlGaN/GaN HEMTs. Further, a correlation between device geometry and the mean momentum relaxation rate of PCF scattering was further established. Devices with a larger ratio of source-spacing (drain-spacing)-to-gate-length [Lgs(gd)/Lg] exhibited stronger PCF scattering strength.