Vertical GaN Schottky barrier diodes on Ge-doped free-standing GaN substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on Ge-doped free-standing GaN substrates grown by hydride vapor phase epitaxy. Detailed material characterization was performed, and the results indicate the superiority of Ge doping in the GaN, which contributed to the SBDs with lower stress, fewer defects and higher quality. Based on the capacitance-voltage and current–voltage measurements performed, SBDs achieved together with a low turn-on voltage V_on (0.71–0.74 V), high current I_on/I_off ratio (3.9 × 10⁷–2.9 × 10⁸), high Schottky barrier height (0.96–0.99 eV), and high breakdown voltage V_b (802 V for a 100 μm diameter). This shows that vertical GaN SBDs on the Ge-doped substrates are promising candidates for high power applications.