Improved rhenium Schottky diodes to n-type gallium nitride

Rhenium deposited by electron-beam evaporation and sputtering was studied for Schottky contacts to n-type gallium nitride (GaN). Barrier heights were investigated via current-voltage, current-voltage-temperature, and capacitance-voltage measurements. Electron-beam evaporated Au/Re/n-GaN diodes exhibited an average Schottky barrier height (SBH) of 0.78 ± 0.04 eV and ideality factor (n) of 1.02 ± 0.01 as deposited, and 0.81 ± 0.03 eV and 1.02 ± 0.01, respectively, when annealed for 5 min at 400°C. On the other hand, sputtered Re contacts offered poor electrical characteristics as deposited with the SBH = 0.38–0.41 eV and n = 1.26–1.73. They improved when annealed for 5 min at 500°C with a SBH = 0.74 ± <0.01 eV and n = 1.02 ± <0.01, yet the sputtered diodes were not as thermally stable. This study highlights the importance of choices made during fabrication of nominally the same structures that can dramatically affect their performance. Damage introduced during sputter deposition can be healed by annealing, but not completely since thermal stability is compromised.