Submicrometer‐thick AlGaN/GaN high‐electron‐mobility transistor (HEMT) epilayers grown on silicon substrate with a state‐of‐the art vertical buffer breakdown field as high as 6 MV cm−1 enabling a high transistor breakdown voltage of 250 V for short gate‐to‐drain distances despite such a thin structure are reported. HEMTs with a gate length of 100 nm exhibit good DC characteristics with a low drain‐induced barrier, going as low as 100 mV V−1 for a VDS of 30 V. Breakdown voltages of each epilayer from the decomposed heterostructure reveals that the outstanding breakdown strength is attributed to the insertion of Al‐rich AlGaN in the buffer layers combined with an optimized AlN nucleation layer. As a result, large signal measurements at 10 GHz could be reliably achieved up to VDS = 35 V despite the use of a 100 nm gate length. These results demonstrate the potential of submicrometer‐thick buffer GaN‐on‐Si heterostructures for high‐frequency applications.

In this work, sub-micron-thick AlN/GaN transistors (HEMTs) grown on a silicon substrate for high-frequency power applications are reported. Using molecular beam epitaxy, an innovative ultrathin step-graded buffer with a total stack thickness of 450 nm enables one to combine an excellent electron confinement, as reflected by the low drain-induced barrier lowering, a low leakage current below 10 µA/mm and low trapping effects up to a drain bias VDS = 30 V while using sub-150 nm gate lengths. As a result, state-of-the-art GaN-on-silicon power performances at 40 GHz have been achieved, showing no degradation after multiple large signal measurements in deep class AB up to VDS = 30 V. Pulsed-mode large-signal characteristics reveal a combination of power-added efficiency (PAE) higher than 35% with a saturated output power density (POUT) of 2.5 W/mm at VDS = 20 V with a gate-drain distance of 500 nm. To the best of our knowledge, this is the first demonstration of high RF performance achieved with sub-micron-thick GaN HEMTs grown on a silicon substrate.