A new acceptor state in CVD-diamond

Homoepitaxially grown CVD-diamond to which H₂S 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. 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. The first ionization energy is attributed to the non-intentional incorporation of boron impurities, in agreement with the measured p-type conductivity. The level at 479 meV has been identified as an acceptor state, and its origin is discussed. The origin of the level detected by Hall measurements at 1.55 eV and by photoconductivity at 2 eV is not yet clear, and it has been tentatively attributed to nitrogen impurities.