High-current, high-voltage AlN p–n junction diodes enabled by compositional grading

AlN p–n junction diodes with low specific ON-resistance (1.6 mΩ cm2), enabling forward current densities >1 kA/cm2, and reverse breakdown fields of 8 MV/cm, were demonstrated. The quasi-vertical device structure consisted of a p-AlGaN anode, an n-AlN drift layer, and an n-AlGaN back contact. The effect of the AlGaN/AlN band offset was studied by comparing devices with abrupt and compositionally graded junctions. Simulation and experimental data suggested that the valence band offset at the abrupt junction significantly limited hole injection into the AlN, limiting the forward current. This problem was mitigated with the use of a compositionally graded junction that showed an order of magnitude higher ON-state current density. These results show that high-current, high-breakdown AlN p–n junction diodes can be achieved by using compositional grading to circumvent the doping problem in p-type AlN.