Fabrication and characterization of metal-semiconductor field-effect transistor utilizing diamond surface-conductive layer

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 О 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 A1 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 (Е/R) inverters with the enhancement mode transistor and resistor, and direct coupled enhancement/enhance-ment (E/Е) inverters with the two enhancement mode transistors have been also fabricated. This Е/R inverter exhibits high voltage gain. For a E/Е inverter, the voltage gain has also been measured as a function of frequency. The high 3-dB frequency (fн) is above 2 MHz. The voltage gain at frequency =/h (Hz) is equal to l √2~ the voltage gain at frequency = 0 (H_z).