Avalanche durability of high-voltage GaN <i>p</i> – <i>n</i> diodes with tunnel junctions as anode contacts

Abstract

Tunnel junctions were applied to anode contacts in high-voltage GaN p–n diodes with sloped mesa terminations. The devices were composed of bottom p–n junctions with low doping concentrations to ensure a high blocking voltage, along with top n++/p++ tunnel junctions with doping concentrations greater than 3 × 1020 cm−3. The formation of fine square-shaped grooves through the tunnel junctions enabled dehydrogenation from the buried p-type layers, resulting in a reduction of the series resistance in the forward current–voltage curves. Repeatable reverse bias sweeps up to avalanche voltages were demonstrated for devices with and without grooves. The differential resistance in the voltage range of avalanche multiplication was reduced by the formation of grooves and by the reduction of the gaps, which corresponded to an increase in acceptor concentrations in the buried p-type layers, as indicated by capacitance–voltage curves. Because holes generated by avalanche events pass through the neutral region in the buried p-type layer, the resistance of this layer needs to be reduced by sufficient dehydrogenation to minimize Joule heating. In addition, GaN p–n diodes with tunnel junction anode contacts having fine square grooves passed a 1 h hold test at a constant current of 1 mA at the avalanche voltage. When the high-voltage p–n junction was in reverse bias, the tunnel junction was in forward bias; holes, therefore, passed through the tunnel junction. The results suggest that tunnel junctions enable the removal of holes generated by avalanche in high-voltage GaN transistors.