Electrical properties of high quality diamond films

Abstract

Significant improvements have been made over the last year in the quality of chemical vapor deposited (CVD) diamond films. In particular, efforts have been made to improve the mobilities and lifetimes of free carriers. Values as high as 4000 cm 2 per V-s have been measured for the combined electron and hole mobilities in the best polycrystalline diamond, which is comparable to that of the best single-crystal IIa natural diamonds. Comparable carrier lifetimes have also been observed, ranging from 150 ps to 1 ns in CVD diamond, compared with 100 to 600 ps in natural IIa diamonds. The films were produced by microwave-assisted CVD, and both polycrystalline and epitaxial films were studied. The carrier mobility and lifetime were measured using transient photoconductivity as a function of electric field and excitation density. Both velocity saturation and electron-hole scattering were observed in the CVD films, similar to behavior measured in natural diamonds. The drift distance at an electric field of 10 kV cm −1 was as high as 15 μm. The improved properties are most likely due to lowered defect densities. Comparable results between epitaxial and polycrystalline films suggest that structural defects may not be the limitation. The improved quality is a significant step toward the production of electronic devices made of diamond, in particular diamond detectors for ionizing radiation. Already CVD diamond has been used to detect ultraviolet light, X-rays and high energy charged particles.