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 ( $10^{4}$ – $10^{6}$ 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 $\mu $ m and net carrier electron concentrations of $4\times 10^{15}$ to $2.5\times 10^{16}$ 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 ( $R_{{{\textrm {sp}}}}$ ) of 2 m $\Omega $ cm $^{2}$ for a BV of 2.6 kV and 2.95 m $\Omega $ cm $^{2}$ 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 mm $^{2}$ , with BVs exceeding 700 V and pulsed (100 $\mu $ s) 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.