Diamond junction FETs based on delta-doped channels

Diamond junction field effect transistors (FETs) utilizing delta-boron-dope d diamond films were fabricated and analyzed. In order to allow full charge modulation by the gate, the total channel sheet charge must not exceed the order of 10(13) cm(-2). However, boron doping shows full activation only f or concentrations above ca 10(20) cm(-3) [1]. This yields a thickness for a fully activated channel in the range of ca 1 nm. To approach such narrow d oping spikes any parasitic boron doping tails need to be eliminated. One po ssible way of achieving this is to compensate boron doping with nitrogen do ping, an extremely deep donor. This results in the formation of a pn-juncti on, where the nitrogen doped part is not activated at room temperature and which therefore represents a semi-insulating (lossy) dielectric at low temp erature and high frequency. At elevated temperature and low frequency the n itrogen doped layer becomes conducting acting as a series resistor to the i nterfacial pn-junction. Using this concept of a lossy dielectric pn-junctio n in the delta-doped channel FET, two gate diode configurations were invest igated. In the first the nitrogen doped (Ib) synthetic diamond substrate se rved as a large area back gate, while in the second the nitrogen doped gate layer was grown on top of the delta-channel. The devices show high drain c urrents of up to 100 mA mm(-1) and full channel modulation even at moderate operation temperatures of 200-250 degrees C. By extrapolation a current de nsity of 1 A mm(-1) is expected for a 0.25 mu m gate length device. (C) 199 9 Elsevier Science S.A. All rights reserved.