Metal-insulator transition in boron-ion-implanted diamond

摘要

We have observed the metal-insulator transition in single crystal, high-purity type-Ⅱa diamond which has been implanted at 77 K with boron ions in multiple steps and annealed at high temperatures between implants. Electrical conductivity measurements made at temperatures in the range 1.5-300 K have shown that, for boron concentrations below the critical concentration n_c which we estimate as 3.9 x 10~(21) cm~(-3), Efros-Shklovskii hopping conduction occurs at sufficiently low temperatures. At the highest concentrations, just-metallic behavior is found, with the low-temperature conductivity governed by the relation σ_(T) = σ(0) + bT~m. The conductivity critical exponent μ is estimated to be 1.7, with a fairly large uncertainty because of the limited number of concentrations on the metallic side of the transition. The high μ value found for this wide bandgap, uncompensated p-type system contrasts with the value μ ≈ 1/2 reported for p-type Si and other uncompensated semiconductors.