Impact of AlGaN and InAlN Barrier Layer Materials on Double-Heterostructure GaN HEMT's Conduction Properties

Gallium-nitride (GaN) based high electron mobility transistors (HEMTs) are widely used in RF applications due to their high breakdown voltage, a consequence of GaN's wide bandgap. This paper investigates a double-heterostructure HEMT with an AlGaN barrier layer, where a two-dimensional electron gas (2DEG) forms due to piezoelectric and spontaneous polarization. We present the dependence of 2 DEG density on aluminum content and the temperature dependence of carrier mobility for an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Al}_{0.4} \text{Ga}_{0.6} ~\mathrm{N}$</tex> barrier layer. The momentum relaxation time approximation is used for numerical calculations of low-field electron mobility, accounting for all relevant scattering mechanisms. Interface roughness (IFR) scattering dominates at low temperatures, while polar optical phonon (POP) scattering primarily determines total mobility at room temperature and above. Furthermore, the barrier layer is modified to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{I n}_{0.14} \mathbf{A l}_{0.86} \mathbf{N}$</tex>, where the 2 DEG forms mostly due to spontaneous polarization. The dependence of 2DEG density on indium content in the barrier layer reveals an increase in 2DEG density, leading to lower on-state resistance. Notable improvements in transconductance are also observed, with a third double heterostructure featuring a thinner <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\operatorname{In}_{0.14} \text{Al}_{0.86} ~\mathrm{N}$</tex> barrier simulated alongside the previous two structures of equal dimensions. This provides guidelines for optimizing GaN-based HEMTs to achieve minimal on-state resistance and high transconductance.