Improvement of transconductance and cut-off frequency in $\hbox {In}_{0.1}\hbox {Ga}_{0.9}\hbox {N}$ back-barrier-based double-channel Al$_{0.3}$Ga$_{0.7}$N / GaN high electron mobility transistor by enhancing the drain source contact length ratio

Abstract

An aluminium gallium nitride / gallium nitride ($\hbox {Al}_{0.3}\hbox {Ga}_{0.7}\hbox {N}/\hbox {GaN}$) high electron mobility transistor (HEMT) is designed at a gate length ($L_\mathrm{G}$) of $0.1~\mu \hbox {m}$, drain-to-source spacing ($L_\mathrm{SD}$) of $3~\mu \hbox {m}$ and drain length to source length ratio ($L_\mathrm{D}$:$L_\mathrm{S}$) of 1. The HEMT is investigated by considering four different heterostructures, namely single channel, single channel with back-barrier, double channel and double channel with back-barrier. A two-dimensional electron gas (2DEG) is formed at the interface of AlGaN / GaN HEMT (DC HEMT). The physical importance of indium gallium nitride (InGaN) as back-barrier is to increase carrier confinement by raising the conduction band of GaN buffer. The double-channel HEMT (DC HEMT) with back-barrier shows the highest current drive. There is an improvement of 3.16% in drain current and an improvement of 4.58% in cut-off frequency at a gate-to-source voltage of $-\,0.5$ V for the DC HEMT with back-barrier compared to the DC HEMT without back-barrier. For further improvement in transconductance and cut-off frequency, the structure of DC HEMT with back-barrier is modified by increasing the drain contact length and decreasing the source contact length, that is $L_\mathrm{D}$:$L_\mathrm{S} = 3$, keeping the drain-to-source spacing unchanged, i.e. $L_\mathrm{SD}=3~\mu \hbox {m}$. There is 32.55% improvement in transconductance and 14.03% improvement in cut-off frequency at a gate-to-source voltage of $-\,0.5$ V for the DC HEMT with back-barrier at $L_\mathrm{D}{:}L_\mathrm{S} = 3$ compared to the DC HEMT with back-barrier at $L_\mathrm{D}$:$L_\mathrm{S} = 1$.