Analysis of Leakage Channel with Different Al Composition back Barriers in AlN/GaN High‐Electron‐Mobility Transistors on Silicon

This study investigates the effect of different Al compositions in the back‐barrier (BB) materials on the off‐state leakage characteristics of AlN/GaN/Al_xGaN high‐electron‐mobility transistors (HEMTs) on silicon substrates. The position of the N‐type parasitic channel within the epitaxial material is further validated. Electrical performance measurements of AlN/GaN/AlGaN HEMTs with varying isolation depths are conducted, and parasitic channels in the unintentionally doped AlGaN BBs are confirmed through isolation leakage and capacitance tests. Transmission line model results reveal that the parasitic channel is an N‐type channel with a sheet resistance of 7078.4 Ω sq⁻¹. Simulations show that the Al composition in the BB layer influences the position of the N‐type parasitic channel. As the Al composition increases to 15%, the parasitic channel contracts from the BB layer into the GaN channel layer. Isolation leakage tests on Al_0.2GaN and AlN BBs, with the isolation depth controlled at the interface between the channel and the BB layers, yield leakage currents of 3.9 × 10⁻⁴ and 2 × 10⁻⁷ mA mm⁻¹, respectively.