Room-temperature electrical conductivity studies of sulfur-modified microcrystalline diamond thin films

The room-temperature electrical conductivity of sulfur-incorporated microcrystalline diamond $(μc-D:S)$ thin films synthesized by hot-filament chemical vapor deposition was investigated as a function of sulfur concentration. The films were prepared using a 0.3% $CH4/H2$ gas mixture and hydrogen sulfide $(H2S)$ as dopant source on intrinsic Si(001) substrates. The $μc-D:S$ films exhibited an increase in $n$-type conductivity with increase in $H2S$ concentration from 0 to 200 ppm, followed by a decrease in conductivity and sign reversal for the films grown with 500 ppm of $H2S.$ These films were also characterized using scanning electron microscopy, atomic force microscopy, and Raman spectroscopy techniques. The findings are discussed in terms of the role of sulfur in the films. The films grown at the highest $[H2S]$ possess the highest carrier concentration $(∼1.07×1017/cm3)$ and the lowest carrier Hall mobility $(0.01 cm2 V−1 s−1).$ Since the conductivity is affected by carrier concentration and crystallinity, the relatively low experimental conductivity values are connected to low mobilities arising from crystal defects and grain boundaries induced by sulfur addition, and to low carrier concentrations due to incomplete ionization of S atoms.