Vibrational dynamics and superconducting properties of CVD grown boron doped diamond films

One of the most intriguing discoveries in the last few decades has been the finding of superconductivity in covalently bonded systems such as MgB2, Si clathrate compound and doped fullerene. This has not only made carbon based materials, a material of focus in the 21st century but also paved new ways to the discovery of some very important semiconducting superconductors such as Si, Ge and Diamond. These materials share a common structure and the mechanism of superconductivity.
 
With increase in the boron concentration in boron doped diamond (BDD), impurity levels aggregate into an impurity band, which beyond a critical concentration of boron (nc = 4.5 x 1021 cm-3) merges with the valence band to become a superconductor. Despite great efforts in the study of the group-IV covalent semiconductors, many unresolved questions and unexplained results require further investigation. The nature of their superconducting coupling mechanism, characterization of their doping level by lattice parameter changes, and the origin of their electronic orderings and superconductivity are still debated issues and require further studies to develop a robust understanding. Also, efficient doping to achieve high Tc in superconducting BDD remains a challenging task. To address the above issues, a series of superconducting boron doped diamond films were deposited using hot filament chemical vapour deposition (HFCVD) technique. A detailed investigation of the impurity band evolution and its vibrational dynamics were carried out as a function of doping concentration. High pressure study of the superconducting BDD revealed that grain the grain boundary carbons undergo a phase change at 14 GPa.