Vertical Power p-n Diodes Based on Bulk GaN

There is a great interest in wide-bandgap semiconductor devices and most recently in monolithic GaN structures for power electronics applications. In this paper, vertical p-n diodes fabricated on pseudobulk low defect density (10⁴-10⁶ cm^-2) GaN substrates are discussed. Homoepitaxial low-pressure metal organic chemical vapor deposition growth of GaN on its native substrate and being able to control and balance the n-type Si doping with background C impurity has allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations of 4 × 10¹⁵ to 2.5 × 10¹⁶ cm^-3. This parameter range is suitable for applications requiring breakdown voltages (BVs) of 600 V-4 kV with a proper edge termination strategy. Measured devices demonstrate near power device figure of merit, that is, differential specific on-resistance (R_sp) of 2 mΩcm² for a BV of 2.6 kV and 2.95 mΩcm² for a 3.7-kV device, respectively. The improvement in the substrate quality over the last few years has resulted in the fabrication of diodes with areas as large as 16 mm², with BVs exceeding 700 V and pulsed (100 μs) currents of 400 A. The structures fabricated are utilized to study in detail the temperature dependency of I-V characteristics, impact ionization and avalanche characteristics, and extract (estimate) modeling parameters such as electron mobility in the GaN c-direction (vertical) and hole minority carrier lifetimes. Some insight into device reliability is also provided.