InAlN/GaN-on-Si HEMTs with an InGaN Back Barrier for mm-Wave Applications

We present InAIN/GaN-on-Si HEMTs with a 26 nm intrinsic GaN (iGaN) channel and a carbon-doped (cGaN) buffer separated by a thin $8 \mathrm{~nm} \mathrm{In}_{0.12}$ GaN back barrier and a buried intrinsic GaN (biGaN) layer. Investigating the influence of varying the cGaN and biGaN layer thicknesses reveals the significance of introducing a biGaN layer to minimise buffer trapping and reduce the large-signal performance penalty. Large-signal characterisation at 28 GHz, with harmonic tuning up to the third harmonic, shows excellent metrics for 80 nm gate length devices, with a respective Gain, $P_{\text {sat }}$, PAE of $12.6 \mathrm{~dB}, 1.06 \mathrm{~W} / \mathrm{mm}$, and 50% at 6 V, and $10 \mathrm{~dB}, 2.6 \mathrm{~W} / \mathrm{mm}$, and 50% at 10 V, positioning them as strong candidates for further optimisation targeting FR2 user equipment applications.