Enhanced performance characteristics of n-ZnO/p-GaN heterojunction light-emitting diodes by forming excellent Ohmic contact to p-GaN

We report significantly improved performance characteristics of n-ZnO/p-GaN heterojunction light-emitting diodes (LEDs) by forming excellent Ohmic contact to p-GaN. An elaborately designed fabrication procedure to suppress ZnO sputtering damage on p-GaN, i.e., a selective SiO₂ passivation of the p-GaN surface, was shown to yield excellent Ohmic contact to p-GaN with a specific contact resistance of 9.8×10^-3 Ω cm², while the reference contact formed on non-protected p-GaN showed non-Ohmic behavior. Heterojunction LEDs fabricated with the improved p-Ohmic contact had much better performance characteristics than did the reference LEDs, i.e., the forward voltages at 2 mA were 5.6 and 16.2 V, the series resistances were 404 and 1693 Ω, and the optical output powers at 3 mA were 56.4 and 19.9 μW for the developed and reference LEDs, respectively.