Evidence of linear Zeeman effect for infrared intracenter transitions in boron doped diamond in high magnetic fields

In this paper, the evolution of the infra-red absorption of high-quality epitaxial diamond films versus boron concentration is reported. Homoepitaxial diamond films were grown by microwave-plasma-assisted chemical vapour deposition on type Ib crystals. From 2e17 to 8e20 1/cm3 of boron were incorporated in the diamond from the gas phase during growth. The main absorption features are (1) a single phonon absorption around 160 meV, (2) a series of three lines at 304, 347 and 363 meV due to excited states of the bound hole, (3) a photoionisation continuum, and (4) a phonon replica of these electronic transitions. The Evolution of these absorption with the boron concentration is presented and discussed. A strong increase in the photoionisation crosssection for boron concentrations above 5e18 1/cm3 is observed. New linear relationships between the boron concentration and the integrated absorption at 347 meV and the photoionisation are proposed. From the evolution of the lines due to transitions to boron-excited states, we deduced the width of the impurity band versus the boron concentration.