Raman characterization of boron-doped {111} homoepitaxial diamond layers

p-type {111} homoepitaxial diamond layers were grown by Microwave Plasma-Enhanced Chemical Vapor Deposition. The variation of the gas phase boron concentration led to solid-state incorporation of boron in the 6 · 1016–3 · 1021 cm− 3 range. Confocal Raman spectroscopy and Raman imaging have been used to investigate this series of homoepitaxial films. As already observed for undoped or phosphorous-doped {111} epilayers, a first noticeable feature was the presence of many sharp and weak lines peaking at random in the 500–2000 cm− 1 range. These peaks were all the most observed that the doping level was low. A number of boron-related Raman lines centered at about 610, 925, 1045 cm− 1 were observed for solid state boron concentrations in the 1.5 · 1018–9 · 1019 cm− 3 range. Above a boron concentration of 3 · 1020 cm− 3, the usual Raman signal of heavily boron-doped diamond was recorded. The thickness of the epitaxial layers, in the 0.2–2 μm range, was too low to allow a more detailed analysis of the zone-center diamond optical phonon.