Abstract: A process of forming high quality diamond films, wherein non-diamond components and crystal defects are significantly reduced. Diamond films are formed on a diamond substrate by vapor-phase synthesis using a source gas, wherein the atomic concentrations of oxygen and carbon, [0] and [C], respectively, in the source gas satisfy the condition that 0.01.ltoreq.[C]/([C]+[O]).ltoreq.0.40. Boron (B) doped p-type semiconducting films can also be formed using the same source gas which further includes a B-containing compound.

Abstract: A diamond film FET according to the present invention comprises a semiconducting diamond layer, a gate, a source, and a drain, wherein said semiconducting diamond layer comprises a semiconducting highly-oriented diamond film grown by chemical vapor deposition, and at least 80% of the surface area of said diamond film consists of either (100) or (111) crystal planes, and the differences {.DELTA..alpha., .DELTA..beta., .DELTA..gamma.} of Euler angles {.alpha., .beta., .gamma.}, which represent the orientations of either (100) or (111) crystal planes, simultaneously satisfy the following relations between the adjacent crystal planes: .vertline..DELTA..alpha..vertline..ltoreq.5.degree., .vertline..DELTA..beta..vertline..ltoreq.5.degree. and .vertline..DELTA..gamma..vertline..ltoreq.5.degree..

Abstract: A is a heat-resisting ohmic electrode on diamond film, including: a p-type semiconducting diamond film; a boron-doped diamond layer provided on the semiconducting diamond film; and an electrode element made of p-type Si selectively formed on the boron-doped diamond layer; wherein the boron concentration in the boron-doped diamond layer is from 1.0.times.10.sup.19 to 1.8.times.10.sup.23 cm.sup.-3, and at least one impurity selected from the group consisting of B, Al and Ga is doped in the electrode element with a concentration from 1.0.times.10.sup.20 to 5.0.times.10.sup.22 cm.sup.-3. The ohmic electrode on diamond film is applicable for electronic devices operative at high temperature.