High electron mobility in nearly lattice-matched AlInN∕AlN∕GaN heterostructure field effect transistors

High electron mobility was achieved in ${\mathrm{Al}}_{1-x}{\mathrm{In}}_x\mathrm{N}∕\mathrm{Al}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ $(x=0.20–0.12)$ heterostructure field effect transistors (HFETs) grown by metal-organic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas density from $0.90\times {10}^{13}\text{to}1.64\times {10}^{13}{\mathrm{cm}}^{-2}$ with corresponding electron mobilities of 1600 and $1410{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ , respectively. The $10\mathrm{K}$ mobility reached $17600{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ for the nearly lattice-matched ${\mathrm{Al}}_{0.82}{\mathrm{In}}_{0.18}\mathrm{N}∕\mathrm{Al}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ heterostructure with a sheet carrier density of $9.6\times {10}^{12}{\mathrm{cm}}^{-2}$ . For comparison, the $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ heterostructure without the AlN spacer exhibited a high sheet carrier density $(2.42\times {10}^{13}{\mathrm{cm}}^{-2})$ with low mobility $(120{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s})$ at room temperature. The high mobility in our samples is in part attributed to $\sim 1\mathrm{nm}$ AlN spacer which significantly reduces the alloy scattering as well as provides a smooth interface. The HFETs having gate dimensions of $1.5\times 40\mu {\mathrm{m}}^2$ and a $5\mu \mathrm{m}$ source-drain separation exhibited a maximum transconductance of $\sim 200\mathrm{mS}∕\mathrm{mm}$ with good pinch-off characteristics and over $10\mathrm{GHz}$ current gain cutoff frequency.