The temperature dependence of the electron and hole impact ionization coefficients in GaN has been investigated experimentally. Two types of p-in diodes grown on bulk GaN substrates have been fabricated and characterized, and the impact ionization coefficients for both electrons and holes have been extracted using the photomultiplication method. Both the electron and hole impact ionization coefficients decrease as the temperature increases. The Okuto-Crowell model was used to describe the temperature dependence of the electron and hole impact ionization coefficients. Based on the measured impact ionization coefficients, the temperature dependence of the breakdown voltage of GaN non-punch through p-n diodes can be predicted; good agreement with experimentally reported results is obtained.

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We demonstrate an ion-implanted triple-zone junction termination extension (JTE) for vertical GaN p-n diodes. Due to the spatial distribution of fixed charge in the triple-zone JTE structure, the peak electric fields at the contact metal edge and at the edge of the JTE are significantly reduced compared to conventional approaches. The forward and reverse characteristics of diodes with conventional single-zone JTE and the triple-zone JTE explored here have been studied and compared experimentally. GaN p-n diodes fabricated using the triple-zone JTE obtain an experimentally measured maximum breakdown voltage of 1.27 kV, appreciably higher than the 1.01 kV achieved using the single-zone JTE structure. The triple-zone JTE design also provides a wider window for fabrication processing and epitaxial wafer growth to achieve the high breakdown voltage compared to single-zone designs. The triple-zone JTE is promising for cost-effective fabrication of GaN power electronics.

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