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

摘要

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 centre dot 10~(16)-3 centre dot 10~(21) 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~(-) 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 centre dot 10~(18)-9 centre dot 10~(19) cm~(-3) range. Above a boron concentration of 3 centre dot 10~(20) cm~(-3), the usual Raman signal of heavily boron-doped diamond was recorded. The thickness of the epitaxial layers, in the 0.2-2 mn m range, was too low to allow a more detailed analysis of the zone-center diamond optical phonon.