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.Comment: 22 pages, 6 figure
