Impact of Buffer Al-Content on 2DEG Mobility and Scattering Mechanisms in Double-Heterostructure GaN HEMTs

This paper investigates the dependence of two-dimensional electron gas (2DEG) mobility in GaN-based double-heterostructure high electron mobility transistors (HEMTs) on aluminum content in the AIGaN buffer layer. Our model uses the momentum relaxation time approximation for numerical calculations of low-field electron mobility, with all relevant scattering mechanisms taken into account. The simulations carried out confirm that carrier mobility is predominantly influenced by polar optical phonon (POP) and interface roughness (IFR) scattering. For that reason, further analysis focused on these two scattering mechanisms, revealing opposite trends in their impact on carrier mobility with varying buffer Al-content. Additionally, the paper discusses the impact of the changes in quantum confinement due to varying buffer Al-content, and establishes a direct connection between quantum confinement and POP/IFR scattering rates, offering comprehensive insights into their interdependences. The findings underline the importance of optimizing buffer aluminum content in AIGaN/GaN/AIGaN heterostructures to achieve higher carrier mobility by finding the optimal trade-off between scattering mechanisms.