T<inf>c</inf> suppression and impurity band structure in overdoped superconducting Boron-doped diamond films

Our work investigates the impurity band and the core excitonic level evolution of a series of systematically boron doped diamond (BDD) films using Raman and X-ray absorption (XAS) spectroscopies. The resistivity versus temperature data shows that Tc of the BDD films achieves a peak at a maximum gaseous phase boron to carbon ratio, [[Formula presented]]max, beyond which Tc drops gradually as a result of excess defect formation, revealing a dome-shaped behaviour. Study of lattice expansion clearly shows the unambiguous presence of substitutional boron atoms beyond [[Formula presented]]max. Direct probe of the impurity band using XAS show a systematic increase in the absorption intensity of the bandgap states which ultimately degrades as the limit of [Formula presented]>[[Formula presented]]max is exceeded. The binding energy of the BDD 1s core exciton reveal a shallow measured value of 0.11 eV. This is less than earlier found values of 0.19 - 1.2 eV, in various reports for intrinsic diamond.