Effect of acceptor traps in GaN buffer layer on source/drain contact resistance in AlGaN/GaN high electron mobility transistors

As-grown GaN buffer layers have a significant electron concentration, which causes an increase in leakage current and a decrease in the breakdown voltage, V${}_{BR}$, of GaN High Electron Mobility Transistors (HEMTs). To prevent this, deep acceptor traps of density, N${}_{AT}$, are added to the GaN layer during growth. While a study on the effect of N${}_{AT}$ on V${}_{BR}$ is available in the literature, that on the effect of N${}_{AT}$ on contact resistance, R${}_c$, of source/drain contacts is lacking. Herein, the following is established using technology computer-aided design simulations calibrated with measured current-voltage characteristics of ungated AlGaN/GaN structures: 1) R${}_c$ increases significantly with N${}_{AT}$ and with the depth of the trap level from the conduction band. For trap level 2.5 eV below the conduction band, R${}_c$ doubles for an increase in N${}_{AT}$ from 1 × 10${}^{16}$ to 5 × 10${}^{17}$ cm${}^{-3}$. 2) The variation of R${}_c$ with temperature is non-monotonic. Over a temperature range of 300-450 K, R${}_c$ is nearly constant with temperature for N${}_{AT}$ = 1 × 10${}^{16}$ cm${}^{-3}$ and decreases by 20% for N${}_{AT}$= 5 × 10${}^{17}$ cm${}^{-3}$, when traps are 2.5 eV below the conduction band. Also, the degradation of the transfer and output characteristics of GaN HEMTs due to a notable increase in R${}_c$ due to N${}_{AT}$ is investigated. (© 2024 Wiley‐VCH GmbH)