Chapter 7 Diamond held effect transistors using h-terminated surfaces

(1)On diamond surface, both H- and O-terminated surfaces are stable structures in air. The former exhibits a relatively hydrophobic surface and p-type conduction at the subsurface. On the other hand, the latter shows a relatively hydrophilic surface and insulating property. Substantial understanding of the surface p-type conductive layer is important.(2)The surface p-type conduction due to H-termination can be used in the surface channel of diamond FET. The high surface carrier density (1013 cm -2) and the shallow carrier distribution are advantageous for current control, the low Schottky barrier height is favorable for ohmic contact, and the low density of surface states (1011 cm -2) is suitable for MISFETs. The MESFET or MISFET with transconductance of 100 mS mm- 1 at a 1 txm gate length have been operated. In these FETs, the cut-off frequency of 10 GHz has been obtained. By the reduction of gate length, much higher frequency operation can be expected.(3)Electrolyte solution gate FET (SGFET) has been operated. The perfect pinchoff and saturation behavior have been demonstrated. The leakage current at the off stage is very small, indicating that ideal FET operation has been obtained in polycrystalline diamonds. On the H-terminated surface channel, the SGFET shows insensitivity to pH, but halogen displays ion sensitivity. This sensitivity is lost when the surface is partially oxidized by ozone. These phenomena can be explained by the difference in the polarity of surface charge between H- and O-terminated surfaces.(4)Using a conductive cantilever of AFM, an H-terminated surface (p-type semiconducting) can be changed to an O-terminated surface (insulating). Similar to nanodevice application, single-hole transistors have been operated using two tunneling junctions and an in-plane-gate FET.