Improvement of Channel Mobility of GaN-MOSFETs With Thermal Treatment for Recess Surface

In this work, a thermal treatment technique under NH3 ambient for the recess surface of GaN-MOSFETs is developed. Immediately following the fabrication process of the recess, the bottoms of these structures have rough surfaces and step-terrace structures cannot be observed because of the plasma-induced damage. However, clear step-terrace structures are formed by the thermal treatment, and the RMS values of the surface roughness decrease from 0.26 to 0.14nm, which is comparable to those of the as-grown epitaxial film. In addition, it is confirmed that concentrations of impurity atoms introduced during the recess fabrication process are decreased by the thermal treatment. The channel mobility of the GaN-MOSFETs without the thermal treatment is 118cm(2)Vs(-1), whereas that of the device whose fabrication process includes the thermal treatment increased to 149cm(2)Vs(-1). These results indicate that the thermal treatment under NH3 ambient is effective for reducing on-state resistance of GaN-MOSFETs.