Analysis of an AlGaN/AlN Super-Lattice Buffer Concept for 650-V Low-Dispersion and High-Reliability GaN HEMTs

In this article, an optimized carbon-doped AlGaN/AlN super-lattice (SL) buffer structure for GaN-based high electron mobility transistors, grown on 200-mm Si wafers is demonstrated. The resulting transistor structure features: 1) maximum vertical breakdown strength as high as 2.72 MV/cm, 2) vertical breakdown voltages (BVs) above 1.2 kV, 3) lateral BVs above 2.2 kV, 4) reduction in buffer traps, which is expected to result in low-dynamic RON, and 5) more than 50 years of extrapolated lifetime at 150 °C under 650-V bias. These were achieved by optimizing growth parameters by systematically varying the SL growth temperature, SL carbon-doping, ammonia flow, and SL pair count with adjusting the total buffer thickness. The detailed analysis shows fundamental improvements compared to a conventional carbon-doped (Al)GaN staircase buffer with the same thickness and comparable growth time.