| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系 === 98 === Enhancement mode (E-mode) AlGaN/GaN HEMTs utilizing Fluorine plasma treatment is investigated in this study. The Fluorine-plasma technique effectively converted the device from conventional depletion mode (D-mode) into E-mode operation. The threshold voltage of the AlGaN/GaN HEMT shifted to +0.7 V after F-treatment. A maximum drain current density of 580 mA/mm was measured at VG = 4 V, and peak transconductance was around 185 mS/mm at VG = 2.5 V. The pulsed ID-VD measurement shows the damages caused by Fluorine plasma treatment in the GaN buffer layer was removed after 400 ℃ annealing for 10 min. In addition, the F-ion treated E-mode HEMTs revealed a tradeoff between threshold voltage and current density. To increase the threshold voltage without sacrificing the current density, an E-mode ALD-Al2O3/AlGaN/GaN MIS-HEMT was fabricated to further increase the threshold voltage. An AlGaN/GaN HEMT with high threshold voltage of 5.2 V was demonstrated as truly normally-off operation along with high turn-on gate voltage of 12.7 V due to the insertion of a 16-nm Al2O3 layer under Schottky gate. The device also demonstrated a maximum drain current density of 520 mA/mm at VG = 11 V without large gate leakage and with a peak transconductance of 100 mS/mm.
E-mode high-breakdown-voltage (HBV) AlGaN/GaN HEMTs were also developed. The developed devices have a breakdown-voltage higher than 200 V were achieved, as defined by drain (or gate) leakage current up to 1 mA/mm. The F-treated E-mode HBV HEMT demonstrated an output current as high as 900 mA under 3-V gate bias, and the device also showed a low leakage current of 150 μA/mm at VD= 200 V. The above results indicate such F-treated E-mode devices developed are promising for future power electronic applications.
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