Effect of interface characteristics on electrical properties of metal-gallium nitride heterostructures.

摘要

The electrical properties of metal-GaN heterostructures due to the defects and nanoscale surface inhomogeneities have been characterized to explore the nature of electron transport and the feasibility of device fabrication.; The effect of nanoscale Pt islands on the contact resistivity and Schottky barrier height in Al/p-GaN contacts was investigated. It was shown that the Al contact with nanoscale Pt islands produced good ohmic characteristics and high reflectance. Current-voltage-temperature (I-V-T) measurements in combination with modeling showed that the electric field enhancement and the increase of the possibility of tunneling due to the nanoscale Pt islands result in an improved ohmic contact.; Electrical transport in nanopatterned contacts to n-GaN using porous anodic alumina (PAA) films as masks was investigated. Non-linear I-V characteristics for the as-grown samples became linear for the reactive ion etched (RIE) and PAA patterned samples. Significant reduction of the specific contact resistivity and the effective barrier height and an increase in the reverse current were observed in the PAA patterned sample. The reduction of the depletion width at sharp corners enhanced the local tunneling current, reducing the specific contact resistivity and decreasing the effective barrier height.; The electrical properties of surface treatments such as KOH treatment and laser etching in unintentionally doped GaN were investigated. KOH treatment produced an increase in the Schottky barrier height and a decrease in the reverse leakage current. By fitting I-V data in the reverse bias region based on the thermionic field emission (TFE) model, it was shown that the experimental results are consistent with the presence of high densities of surface states, which were reduced appreciably by the KOH treatment. Laser etching yielded an increase of interface trap density and degraded the rectifying I-V characteristics. Post-treatment for the laser etched samples with thermal annealing in an N2 ambient followed by KOH treatment improved the rectifying characteristics. These results suggest that the KOH treatment together with thermal annealing is effective in improving the rectifying characteristics of Schottky barriers to n-GaN and has a potential for device fabrication.