Summary form only given. Based on ideal materials data, a power handling capability above 20 W/mm may be predicted for diamond FET devices. Even discarding n-channel devices due to the lack of donor doping, 10 W/mm may be feasible. However, extrapolation of state-of-the-art FETs yields only 0.2 mW/mm, mainly due to incomplete activation of the deep acceptor. Here, an alternative approach is discussed, where the hole conduction of a hydrogen terminated surface is used as channel in a MESFET configuration. This layer is activated at room temperature and contains approximately 10/sup 13/ cm/sup -2/ sheet charge. The electrical properties of metal contacts to this surface are work function dependent and ohmic as well as Schottky barrier contacts can be realized. In this case Au is used for the source and drain contacts and Al for the gate. In this configuration the FET is pinched off at zero gate bias and therefore operating in enhancement mode. Devices have been fabricated on synthetic 1b diamond substrates (Sumicrystal(R)) of 3/spl times/3 mm/sup 2/ surface area. These substrates are heavily nitrogen doped and insulating. The active surface layer is situated on a 100 nm thick, nominally undoped buffer layer, grown by microwave plasma CVD in a H/sub 2/ atmosphere containing 1.5% CH/sub 4/ at 590/spl deg/C and a pressure of 30 torr. After growth, the surface is H-terminated. The contact areas surrounding the active device were insulated by oxygen termination using a RF-plasma. The contacts were deposited by evaporation and patterned by lift-off.
展开▼
