Fabrication and Characterization of Metal-Semiconductor Field-Effect Transistor Utilizing Diamond Surface-Conductive Layer

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Abstract
Metal-semiconductor field-effect transistors (MESFETs) have been fabricated using the p-type surface-conductive layer of undoped homoepitaxial diamond film on the surface. The layers have been employed as the channel of MESFETs. Since the surface-conductive layer is ultrathin, the depletion region has already closed the surface-conductive channel at the gate voltage of 0 V, i.e., these MESFETs exhibit the enhancement mode (normally off-mode). The threshold voltages are -1.6 V and -0.7 V in the case of Al and Pb gate respectively. These MESFETs also exhibit channel pinch-off and complete saturation of drain current, and high transconductance of 2.5 mS/mm at room temperature. This value is the highest of all diamond FETs at present. enhancement/resistor (E/R) inverters with the enhancement mode transistor and resistor, and direct coupled enhancement/enhancement (E/E) inverters with the two enhancement mode transistors have been also fabricated. This E/R inverter exhibits high voltage gain. For a E/E inverter, the voltage gain has also been measured as a function of frequency. The high 3-dB frequency (f H) is above 2 MHz. The voltage gain at frequency=f H (Hz) is equal to 1/√ 2 the voltage gain at frequency=0 (Hz).