Charge transport in heavily B-doped polycrystalline diamond films

Abstract

Temperature-dependent conductivity and Hall measurements have been carried out on heavily in situ B-doped polycrystalline diamond films in a temperature range from ∼100 to 750 K. The slope of the conductivity is clearly non-Arrhenius leading to a pronounced tail at low temperatures. Carrier transport at low temperatures is dominated by variable range hopping. The activation energy decreases with increasing doping concentration and the most heavily doped diamond films show metallic behavior above room temperature. Hole carrier concentrations up to 1.8×1021 cm−3 were measured in agreement with secondary-ion-mass spectroscopy investigations.

Electronic and optical properties of boron-doped nanocrystalline diamond films

“…6 as a function of the boron concentration. In the figure, the activation energies reported for single crystalline diamond films [18][19][20] and polycrystalline diamond 46,47 with the conductivity and carrier concentration data discussed later. Fig.…”

“…9 as a function of boron concentration, together with the theoretical predictions of ionized impurity scattering and grain boundary scattering expected for polycrystalline material. 49 The carrier mobility dependence on boron doping for single crystalline 46 and polycrystalline 47 diamond films have also been plotted in Fig. 9 for comparison.…”

“…15,32 In high quality PCD films, where neither nitrogen nor boron dopants contribute to conduction, the measured activation energy of the conductivity, E A ~ 1-1.7 eV, was attributed to the thermal activation of carriers in π-π* bands introduced by sp 2 -bonded carbon present in the grain boundaries. 22 The room temperature conductivitiy of single crystalline diamond films, 19,46 polycrystalline diamond films, 47 and our NCD films are shown as a function of boron concentration in cm -3 . 23,24 As the graph reveals, the conductivity of the weakly boron-doped NCD films is about three orders of magnitude lower compared to homoepitaxial boron doped films.…”

Superconductivity in diamond

“…Increasing the concentration to 10 20 cm −3 gradually decreases the activation energy 9,10 , and for n≥10 20 cm −3 , the electrical conductivity acquires metallic-like behaviour near room temperature [8][9][10][11] that signals an insulator-metal transition near this concentration. A metallic-like conductivity has not been found, however, at low temperatures for any presently available B concentration, which has reached (2-3)×10 21 cm −3 (refs 8-11).…”

“…Electrical transport studies of B-doped diamond, including high-pressure synthesized crystals and CVD (chemical vapour deposition) films, find that low boron concentrations n≈10 17 -10 19 cm −3 give a semiconducting conductivity with an activation energy of ~0.35 eV (refs 7-11). Increasing the concentration to 10 20 cm −3 gradually decreases the activation energy 9,10 , and for n≥10 20 cm −3 , the electrical conductivity acquires metallic-like behaviour near room temperature [8][9][10][11] that signals an insulator-metal transition near this concentration. A metallic-like conductivity has not been found, however, at low temperatures for any presently available B concentration, which has reached (2-3)×10 21 cm −3 (refs 8-11).…”