Vertical GaN P-N Power Diodes with over 5 kV Breakdown Voltage

This work reports vertical GaN PN diodes with over 5 kV breakdown voltage. The devices were fabricated on a 2” Ammonothermal NEAT GaN substrate. The electron concentration of the substrate is &gt; 8 ×10¹⁸cm⁻³ with an average dislocation density of ~ 1×10⁵cm⁻². The drift layer was grown by metalorganic chemical vapor deposition (MOCVD) at a growth rate of 5 μm/hr. The epi-layers on top of the substrate consist of 2 μm thick n+ layer (2×10¹⁸ cm^-3) followed by ~ 28 μm n^- drift layer (1×10¹⁵ cm^-3), and a 500 nm p-GaN layer (1×10¹⁷ cm^-3) topped with a thin p⁺-20 nm GaN layer (5×10¹⁷ cm^-3). The device has a size of 500 μm in diameter. The device structure was designed based on analytical calculations and numerical simulations. After optimization in numerical simulations, a design with 6 Guard Rings (GR) was chosen for electrical field management. In addition to the GRs, a 1.7 μm spin-on-glass and a field plate design were included. Simulation results show that the electric field is peaked at 3.5 MV/cm at the edge of the GR under a reverse bias of 6.4 kV. The GRs were implemented by nitrogen ion implantation at a dose of 3.2×10¹³ions/cm⁻². A Ti/Al based alloyed contact was used as the back cathode for n-GaN and a Ni/Pt/Au based alloyed contact was used as top anode for p-contact. The n-contact resistance was measured to be 6.1×10^-6Ωcm² and the p-contact resistance was 9.2×10^-5 Ωcm², respectively. The device exhibited an avalanche breakdown at 5093 V, showing a remarkable agreement with numerical simulation with a breakdown efficiency of &gt; 79%. The reverse leakage current density is below 1×10^-7A/cm² until 200 V and ~ 1×10^-5A/cm² at 3 kV. For forward characteristics, the device has a turn-on voltage of 3.85 V at 100 A/cm² and has a current density of over 500 A/cm² below 5.0 V. The specific on resistance for this device is 2.45 mΩ.cm². Considering the measured breakdown voltage and specific on-resistance, the device has a Baliga figure of merit of 10.6 GW/cm². Considering the p-contact resistivity from the TLM structure next to the device (1.4 mΩcm²)and the specific on-resistance of the device, the electron mobility in n-drift layer is approximately 1000 cm²/Vs. To the best of our knowledge, this is the first GaN pn power diode that demonstrates over 5 kV breakdown with a drift layer of less than 30 μm.<br/><br/>Acknowledgment: ARPA-E (DE-AR0001036), and U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, FY18/FY19 Lab Call.