Comparison of the electric properties of single-crystal and polycrystalline diamond by hall effect and capacitance-voltage measurements

Abstract

The transport properties of type IIb (naturally B-doped), single-crystal diamond were investigated by differential capacitance-voltage ( C- V) measurements, Hall effect measurements and resistivity measurements. The results for the Hall effect and resistivity measurements on single-crystal samples were compared with similar measurements on polycrystalline samples grown by microwave-assisted chemical vapor deposition. The C- V and Hall effect measurements on single crystal, type IIb diamond samples showed consistent results. Temperature-dependent resistivity measurements verified an activation energy of 0.36 eV, while room temperature Hall effect measurements on a (100)-oriented, type IIb single crystal indicated that the active carrier concentration was 2.1 × 10 13 cm −3. This result was consistent with total B concentrations measured by both C- V and secondary ion mass spectroscopy (SIMS). The transport properties for polycrystalline samples were not as good as those for single-crystal samples. At room temperature, the mobilities were 3 and 10 cm 2 V −1 s −1 for two in situ doped polycrystalline thin films, as compared with 325 cm 2 V −1 s −1 for the single-crystal sample. For one in situ doped sample, the activation energy was measured to be 0.05 eV and the room temperature carrier concentration was 1.8 × 10 16 cm −3, while SIMS indicated that the total atomic B concentration was 5 × 10 18 cm −3. The relatively low carrier concentrations measured in the polycrystalline samples may be indicative of a high level of compensation (about 65%) or trapping of charge at the grain boundaries, leading to a depletion of carriers in the crystallites.