High performance normally-off GaN MOSFETs on Si substrates

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.