Electrical and optical measurements of CVD diamond doped with sulfur

Homoepitaxially grown chemical-vapor-deposition diamond to which ${\mathrm{H}}_2\mathrm{S}$ was added during the growth was analyzed by electrical and optical measurements in order to investigate the nature of sulfur as a dopant in diamond. Hall measurements were carried out at low and high temperatures. In the low-temperature range (175–290 K), p-type conduction was found, with an activation energy of 360 meV. A hole concentration of $5.6\times {10}^{12}{\mathrm{cm}}^{-3}$ with a mobility of 270 ${\mathrm{cm}}^2$ ${\mathrm{V}}^{\mathrm{-}1}$ ${\mathrm{s}}^{\mathrm{-}1}$ was measured at room temperature. On the other hand, at high temperatures (650–900 K), n-type conductivity was observed with a carrier activation energy of 1.55 eV. Using photoconductivity spectroscopy, four dominant ionization energies are detected at 371 meV, 479 meV, 1 eV, and 2 eV. Excited states of the two shallow levels were deduced from oscillatory photocurrent and photothermal ionization. The first ionization energy is attributed to the effect of an unknown boron contamination source, in agreement with the p-type conductivity measured. The origin of the level detected by Hall measurements at 1.55 eV and by photoconductivity at 2 eV is not clear yet, and it has been tentatively attributed to nitrogen impurities. The origin of the new acceptor state measured at 479 meV above the valence-band edge is also discussed.