Modeling of the Charge-Voltage Characteristics of AlScN/AlN/GaN Heterostructures

With evolving research into III-nitride materials for various high-frequency applications, the ternary material Sc x Al 1-x N (referred to as ScAlN throughout) has emerged as an attractive candidate due to its exceptional piezoelectric effect (the piezoelectric moduli $e_{33}=9.125x+1.471(1-x)-6.625x(1-x)$ increases rapidly with an increasing $x$ [1]), ferroelectricity [2], and high spontaneous polarization [3]. Current research in ScAlN/AlN/GaN heterostructures is at a nascent stage and the potential benefits of utilizing ScAlN in high electron mobility transistors (HEMTs) are not quantified. We study the impact of alloy composition and barrier thickness on the density and the gate modulation efficiency of the two-dimensional electron gas (2DEG) in various ScAlN/AlN/GaN heterostructures (Figs. 1(a)&(b)). We identify the design constraints that must be met for this heterojunction to be used effectively within a HEMT architecture. An analytic charge-voltage (Q-V) and capacitance-voltage (C-V) model is developed and validated against Schrodinger- Poisson simulations. The analytic model is extended to 2D to account for the impact of drain bias on the channel charge for an ScAlN/AlN/GaN HEMT, and the role of channel transmission coefficient (i.e., diffusive versus quasi-ballistic (QB) transport) on Q-V and C-V is examined.