Influence of methane concentration on the electric transport properties in heavily boron doped nanocrystalline CVD diamond films

摘要

A study is presented on the morphology and electric properties of heavily boron-doped nanocrystalline diamond (B:NCD) thin films (=150 nm) grown with two different C/H-ratios (1% and 5%) and a fixed 5000 ppm B/C-ratio in gas phase on fused silica substrates. AFM measurements confirm that a higher C/H-ratio leads to smaller grains and more grain boundaries. Electric transport measurements reveal a higher resistivity and a lower mobility as function of the C/H-ratio for all temperatures measured. The resistivity of the 1% sample is almost not temperature dependent while the 5% sample is much more temperature dependent. The electric transport properties of the grain boundaries, more present in the 5% sample, can be responsible for the difference in transport properties of both samples. The active boron concentration, calculated from the electric transport measurements, is remarkably higher for the 5% sample which indicates there is more boron incorporation for higher C/H-ratios. Although both samples are disordered metals, the 1% sample with the least grain boundaries tends more to the behavior of a highly doped single crystalline diamond film, which behaves like a real metal when heavily boron-doped.