Properties of GaN and AlGaN Schottky contacts revealed from I–V–T and C–V–T measurements

Interface properties of metal/GaN, AlGaN Schottky structures formed on oxide-etched and intentionally oxidized surfaces are studied by I–V–T and C–V–T measurements. The characteristics support the previously proposed “surface patch” model, where the patches with low Schottky barrier heights (SBHs) cause a leakage current. The true SBHs were obtained from high-temperature I–V curves with S-values of 0.28 and 0.20 for n- and p-GaN samples, respectively. Thermally oxidized GaN surfaces represented a reduction of the effective SBH for Ni/n-GaN sample. I–V–T characteristics showed that the leakage current due to surface patches is comparable with that of the oxide-etched sample. The current drift was less than 0.1% within the range of 1–104 s. On the other hand, anodized GaN surface led to increase of the SBH up to 0.3 eV, owing to formation of a relatively thick oxide layer. The oxide-etched Au/n-Al0.2Ga0.8N sample on HEMT wafer represented a considerably reduced effective SBH at RT, because of a tunneling leakage current. However, the true SBH was deduced to be 1.4 eV from the I–V–T characteristics. The annealing in N2 flow was again effective to improve the interface properties.