In this paper, we discuss the progress in the application of silicon‐on‐diamond (SOD) and chemically vapour deposited (CVD) diamond wafers as an alternative solution to silicon and silicon carbide (SiC) substrates to enhance heat dissipation away from the active region of AlGaN/GaN high electron mobility transistors (HEMT) while decreasing thermal degradation due to thermal effects. The superior thermal conductivity and insulating properties of polycrystalline diamond (8–15 Wcm/K) free‐standing wafers have demonstrated certain advantages, mostly evident in the device performance and reliability. Two unique diamond growth applications engineered by sp3 Diamond Technologies Inc., and Group4 Labs Inc., are discussed and device performance data is presented from early attempts to our most current device research efforts. As single‐crystalline diamond wafers (∼20 Wcm/K) become more accessible and affordable, it is expected to see significant improvement over the current state of this technology.

We report on a dc/RF performance of lattice-strained AlInN/GaN high-electron mobility transistors (HEMTs) on SiC substrate. HEMT devices were fabricated with gate periphery of 2 x 150 mu m with an 80-nm T-gate and similar to 2.5-mu m source-drain spacing. Fabricated devices simultaneously demonstrated up to 2.11 A/mm with f(t-ext) = 104 GHz and f(t-int) = 113 GHz. The high performance is attributed to the combination of low R-sh similar to 230 Omega/sq (mu similar to 1079 cm(2)/V . s, n(s) similar to 2.39 x 10(13) cm(-2)) and thin similar to 110-angstrom total barrier thickness with a short gate length. Other device parameters include R-c = 0.29 Omega . mm, I-g,I-leak = 27.9 mu A/mm, g(m,peak) = 432 mS/mm, and V-th = -5.8 V. To our knowledge, this is among the highest current densities reported for any HEMT operating with a unity current gain frequency exceeding 100 GHz.