Advantage on Superconductivity of Heavily Boron-Doped (111) Diamond Films

The superconductivity transition temperatures Tc(onset) of 11.4 K and Tc(offset) of 7.4 K, which are the highest in diamond at present, are realized on homoepitaxially grown (111) diamond films with a high boron doping concentration of 8.4E21 cm-3 (4.7 atomic percent). Tc values of (111) diamond films are more than twice as high as those of (100) films at the equivalent boron concentration. The Tc of boron-doped (111) diamond increases as the boron content increases up to the maximum incorporated concentration and is agrees with the value estimated using McMillan's equation. The advantageous Tc for (111) diamond films is due to the higher carrier concentration which exceeds its boron concentration.