Diamond RF FETs and other approaches to electronics

Diamond semiconductor possesses exceptional physical properties, such as high thermal conductivity, high breakdown field, and high mobility, and is therefore expected to offer the highest performance among semiconductors as high-frequency, high-power transistors. At present the most critical issue in achieving diamond transistors is the lack of an n-type or p-type dopant with low activation energy. This paper reviews approaches towards electronic-device application of diamond done mainly by NTT Basic Research Laboratories. First it describes our diamond field-effect transistors with 0.1-μm gate length, which exhibit high cut-off frequencies for the current and power gains, f_T and f_MAX, of 45 GHz and of 120 GHz, and output power density of 2.1 W/mm at 1 GHz. Next it shows how doping efficiency in ion implantation can be improved by using high-pressure high-temperature annealing. Finally, it describes our concept of diamond/ nitride heterostructure and presents results that confirm its feasibility.