The enhancement mode AlGaN/GaN hybrid MOS-HFETs on Si substrates have been demonstrated. The breakdown voltage of over 1.71 kV was achieved by investigating the epitaxial structure. Furthermore, a high integrity SiO 2/Al2O3 gate stack has been demonstrated for GaN MOSFETs. The SiO2 film formed on GaN by the MW-PECVD exhibits good properties compared that by the LP-CVD. Then, by incorporating the advantages of both of SiO2 with a high insulating characteristics and Al2O3 with good interface characteristics, the SiO 2/Al2O3 gate stack structure has been employed in GaN MOS devices. It is shown that a low interface state density between gate insulator and GaN, a high breakdown field, and a large charge-to-breakdown by applying 3-nm Al2O3 in this structure. The SiO 2/Al2O3 gate stack has also been applied to AlGaN/GaN hybrid MOS-HFET and excellent properties with the threshold voltage of 4.2 V and the maximum field-effect mobility of 192 cm2/Vs are shown in the transistor.
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