| Summary: | 碩士 === 國立虎尾科技大學 === 光電與材料科技研究所 === 95 === In this study, we investigated the performance of the n-GaAs MOSFET that the gate oxide was directly grown on the semiconductor surface using photoelectrochemical (PEC) oxidation method.
To investigate different PEC oxidation conditions for n-GaAs by PEC method, adjust pH value to control growth rate of n+-GaAs. To annealed PEC oxide under 200, 300 and 400oC in the oxygen ambiance of 10, 20, 30 and 40 minutes respectively by furnace, respectively. After annealed 30 minutes that the depth tend to become stable, then we got a smooth surface that after 300oC annealed by AFM, and analysis the compose of oxide are oxidation of gallium and arsenic by EDX, XRD, AES and XPS. We find the oxidation state of oxide increase comply with temperature of 200, 300 and 400oC by XPS.
Finally, the PEC oxidation method was used to grow the GaAs oxide layer as the gate oxide of the MOS diodes and GaAs MOSFETs. Unfortunately, the PEC oxide layers were easily dissolved in the acid and alkali solutions. Therefore, the SiOx layers were deposited on the PEC oxide layers as the protected of the PEC. In this thesis, we fabricated six MOS diodes with different gate oxide (No.1~No.6). The six kinds of gate oxide were PEC oxide (40nm), SiOx(10nm)+PEC oxide(40nm), SiOx(10nm)+PEC oxide(200oC, 33.6nm), SiOx(10nm)+PEC oxide(300oC, 26.4nm), SiOx(10nm)+PEC oxide(400oC, 22.8nm) and SiOx(50nm), respectively. From the C-V measurement, the dielectric constant of the six kinds MOS diodes (No.1 to No.6) is 7.7, 7.2, 8.2, 8.9, 9.1 and 3.9. The interface state density of five kinds MOS diodes (No.1 to No.5) is 8.22×1011, 7.85×1011, 7.47×1011, 7.28×1011 and 7.45×1011 cm2eV, respectively.
We also fabricated a GaAs MOSFET with non-anneal PEC oxide layer as the gate oxide. The drain-source situation current-drain-source voltage (IDS-VDS) and the associated extrinsic transconductance (gm) of the MOSFET were measured by Agilent 4156C semiconductor parameter analyzer. When the MOSFETs were biased at VDS=2.4V, the output current was equal to 101mA/mm at VGS=0V. At VGS=�{2.5V, the drain current was close to zero. This phenomenon indicated that the MOSFETs could be biased in a cut-off mode. The maximum associated extrinsic transconductance was 65mS/mm at VGS = �{0.3V.
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