P-type and N-type Conductivity in Nanodiamond Films
Nanodiamond films can exhibit wildly variable carrier transport mechanisms depending on the crystallite size, grain boundary volume fraction, dopant and dopant concentrations. Films constituting larger grain sizes (>30 nm) tend to exhibit higher intrinsic resistivity and follow conventional transport mechanisms, such as band transport, intermediate variable range hopping and metallic conductivity with increasing dopant concentration. At very high doping concentrations and low temperatures they can be superconducting. Smaller grain size films (<30 nm) generally exhibit lower intrinsic resistivity and mostly variable range hopping transport due to a high density of states within the bandgap. These films tend to have higher optical absorption coefficients than those with larger grains sizes.