Influence of the crystalline structure on the electrical properties of CVD diamond films

[100], [110] and non-textured polycrystalline diamond films were deposited by microwave plasma enhanced chemical vapour deposition. Resistive devices with coplanar and sandwich electrical contacts were made to characterise and compare these films towards their use as radiation detector. Current-voltage measurements in the dark and under UV light and X-ray radiation were carried out. The crystalline structure of the film is shown to have a significant influence on its electrical properties and on their sensitivity to UV and X-ray radiation. Film bulk resistivities range from 1 x 10(12) for the [100] textured films to 5 x 10(14) Omega cm for the [110] textured films. We found that the [100] textured film has the highest carrier drift length before trapping (mu tau E, where mu and tau are the carrier mobility and lifetime and E is the applied electric field) while the non-textured film has the lowest mu tau E. The presence of nitrogen in a [100] textured film is shown to increase its resistivity by more than two orders of magnitude owing to compensation effect, but it reduces the carrier drift length before trapping by a factor of 2.