Compositionally Graded III-N HEMTs for Improved Linearity: A Simulation Study

As is well known, a roadblock to realizing the full potential of GaN high-electron mobility transistors (HEMTs) for power amplifier applications is the peaked nature of the transconductance and the resulting power-gain roll-off exhibited by these devices. Motivated by promising work on compositionally graded HEMT designs, in this paper we explore this design solution using the numerical device simulation. Among other things, we examine the consequences of saturation velocity, grading profile, alloy scattering, and device scaling. In addition, lumped element modeling of the large-signal behavior is carried out to assess the power amplifier performance. We also compare the graded approach with another known method of linearity improvement in which the source resistance is reduced. In general, we find much to recommend in the graded-channel approach, especially for gate lengths greater than about 100 nm.