Simulations of Junction Termination Extensions in Vertical GaN Power Diodes

Simulations of reverse breakdown behavior of GaN power diodes with junction termination extensions (JTEs) are presented. The p-type JTE is located at the edge of the main p-n-junction, and under reverse bias, the charge in the JTE causes spreading and reduction of the peak electric fields to avoid premature avalanche breakdown. To determine the available charge in the JTE, it is shown that the electric field under reverse bias causes severe band bending within the JTE and full ionization of the Mg acceptor. Therefore, all the Mg dopants contribute charge and determine the performance of the JTE. The dependence of the breakdown voltage on the JTE's acceptor concentration and thickness is shown. When the JTE is properly designed, the simulations show improved reverse breakdown behavior and breakdown efficiencies approaching 98% of the ideal limit for planar geometry. Finally, the challenges of creating JTEs within GaN power diodes are discussed.