Fabrication and Characterization of High-Breakdown and High-Power GaN HEMTs

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We have studied the fabrication and characterization of GaN HEMT to realize the high-breakdown and high-power GaN HEMTs. The main results we have obtained are as follows.1. It has been clarified that the off-state breakdown voltage is dominated by the electrons injected from the gate electrode.2. The gate leakage current which affects the breakdown voltage could be decreased in the GaN MISHEMTs with Si_3N_4 gate insulator.3. The off-state breakdown voltage of the GaN MISHEMTs has been increased from 70-80 V of the conventional GaN HEMTs to 160-200 V.4. The current collapse which is one of the dominant factors to decrease the output power of the conventional GaN HEMTs was suppressed in the MISHEMTs.5. It has been demonstrated that the drain current DLTS is effective in studying the transient behavior of the GaN HEMTs. It has also been clarified, using this technique, that the positive peak originating the surface states has been suppressed in the MISHEMTs.6. The issue of small transconductance of the Si_3N_4 MISHEMTs has been solved by using HfO_2 with high dielectric constant as a gate insulator.7. The inclined gate recess structure has been proposed to improve the high-speed performance of the HEMTs. It has been shown that the proposed structure is effective in improving the device performance based on the device simulation and on the device fabrication.