Some peculiarities of doping by boron and electrical conductivity of diamond synthesized under low and ultra-high pressures

This study compares some of the peculiarities of doping by boron and the electrical conductivities of diamonds synthesized under low (less than 1 bar) and ultrahigh (45 kbar) pressures. Regardless of the great difference in the growth medium and growth conditions of diamond under low and ultrahigh pressures, some general trends are observed: (1) boron mainly enters into the growth pyramid of the octahedron, whereas the degree of doping in the cubic growth pyramid is relatively low; (2) the activation energy of conductivity equals 0.37 eV for the degree of doping of no more than 10 to the -19/cm-cubed; (3) the degree of doping during crystallization of the epitaxial films on the (111) face of the seed diamond crystal attains 2.6 at. pct, i.e., it may exceed the maximum level of doping for diamonds grown under ultrahigh pressure; (4) the spatial distribution of boron in polycrystalline films of gas-phase diamond is inhomogeneous, and the mean concentration of boron is 0.1 at. pct as determined by photoelectron spectroscopy; and (5) single crystals doped by boron in the general case contain the donor nitrogen impurity, which considerably influences the electrophysical properties as a result of the formation of neutral B-N pairs in diamond and the compensation effect.