Abstract
In this study, AlGaN/GaN HEMTs on a silicon substrate were fabricated. The devices of linear type and finger type are measured. There are two main topics in this study. One is to investigate the effects of three different gate structures, including Schottky gate, metal-insulator-semiconductor(MIS) gate, and recessed MIS gate. The other one is to compare the effects of different epi structures.Their breakdown behaviors will be compared From the measurement results, among different gate structures,MIS gate devices have the largest saturation current. Compared with MIS gate, the recessed MIS gate devices can shift the threshold voltage from -12.13V to -5V, toward E-mode operation. In the measurement of forward and reverse gate bias, the MIS gate devices show at least 4 order lower gate leakage current than the Schottky gate devices.To enhance the total current, the multiple finger devices have been fabricated. The largest total current of a multiple finger device can achieve 0.65A, which corresponds to 201mA/mm. On the breakdown characteristic, the highest breakdown voltage of a Schottky gate device is 2370V on sample A with Lgd=60-μm when the substrate is floating and the devices are tested with fluorinert immersion. However, the MIS gate devices show a lower breakdown voltage of. This phenomenon is also observed on sample B. On the other hand, the recessed MIS gate devices do not sustain more than 100V, because of a much larger gate leakage current.