| In this dissertation, researches about normally-off mode AlGaN/GaN MOS HEMT device utilizing gate recession and p-GaN gate with high-k gate oxide for high power application have been investigated.;Two technologies of gate recession and p-GaN/AlGaN p-n junction are utilized in this research, for achieving normally-off mode AlGaN/GaN HEMT devices. With the ALD grown HfO2, Al2O3, ZrO 2, the electrical characteristics like high threshold voltage for normally-off mode, low forward gate leakage current, large gate swing are improved. After gate recession with different depths and deposited high-k gate dielectrics, the electrical measurement results of gate recessed AlGaN/GaN HEMT with ZrO 2, HfO2, and Al2O3 show the extremely low leakage current of 10-11 A/mm and high Ion/Ioff ratio of 107. Gate recessed GaN MOS HEMT with 10 nm HfO2 shows the highest Vth of +3.07 V, maximum drain current of 500 mA/mm, sub-threshold slope of 111 mV/dec, and maximum trans-conductance of 225 mS/mm.;AlGaN/GaN MOS HEMT using p-GaN gate with high-k gate dielectrics of Al 2O3, ZrO2, and HfO2 was developed to demonstrate normally-off mode and a low leakage gate current for high power application. After gate oxide deposition of 10 nm high-k gate dielectrics, the electrical measurement results of p-GaN/AlGaN MOS HEMTs demonstrate the extremely low leakage current of 10-11 mA/mm and high Ion/Ioff ratio of 107. P-GaN/AlGaN MOS HEMT with 10 nm HfO2 shows the highest Vth of +2.1V, maximum drain current density of 585 mA/mm, sub-threshold slope of 105 mV/dec, and maximum trans-conductance of 250 mS/mm.;We developed Au-free & normally-off mode AlGaN/GaN MOS HEMT using gate recession and p-GaN gate with Pt based ohmic/gate metallization, instead of Au. In addition, high-k gate dielectrics of 10 nm HfO2 and Al2O3 are added to present a low gate current leakage. With different RTA temperatures, electrical measurement results are compared and GaN MOS HEMT with 10 nm HfO 2 shows the better electrical performaces of highest Vth of +2.58 V, maximum current density of 450 mA/mm, maximum trans-conductance of 170 mS/mm, and the lowest sub-threshold slope of 110 mV/dec. These results present ALD grown-HfO2 is also a good candidate for developing Au-free AlGaN/GaN MOS HEMT operated by normally-off mode. |
