The origins of leaky characteristics of Schottky diodes on p-GaN

The possible origins of the leaky characteristics of a Schottky barrier on p-GaN have been investigated. The as-grown samples did not show any electrical activity using Hall measurements. Ni diodes made on as-activated samples, either at 950°C for 5 s or at 750°C for 5 min exhibited quasiohmic behavior. Upon sequential etching of the sample to remove a surface layer of 150 Å, 1200 Å, and 5000 Å from the sample, the I-V behavior became rectifying. I-V-T measurements showed that the slopes of the lnI-V curves were independent of the temperature, indicative of a prominent component of carrier tunneling across the Schottky junction. C-V measurements at each etch-depth indicated a decreasing acceptor concentration from the surface. The highly doped (>1.7 × 10¹⁹ cm^-3) and defective surface region (within the top 150 Å from surface) rendered the as-activated Schottky diodes quasiohmic in their I-V characteristics. The leaky I-V characteristics, often reported in the literature, were likely to originated from the surface layer, which gives rise to carrier tunneling across the Schottky barrier. This highly doped/defective surface region, however, can play an important role in ohmic contact formation on p-GaN.