  The intensive development of technology for fabrication semiconducting CVD
diamond layers poses an important task of developing a precise and
non-destructive method for estimation the boron content in thin epitaxial
layers. For bulk and uniformly doped diamond samples, the infrared optical
spectroscopy successfully performs such a role. Here we propose a correct
method to determine the boron concentration in CVD homoepitaxial diamond layers
from FTIR spectra. The method is the natural advancement of the existing
technique for bulk samples. The feature of the novel technique is the accurate
accounting of passing radiation through a multilayered structure with different
thicknesses of absorbing media for special absorbing mechanisms. For this
situation, an expression for the effective optical density is obtained. We have
demonstrated the benefit of the method for a set of samples with CVD
homoepitaxial layers grown on various HPHT substrates with and without nitrogen
impurity. The measured FTIR spectra were subdivided into relevant sections
responsible for the specific absorption mechanisms, and the correct amplitudes
of the boron absorption peaks were derived. The data obtained from FTIR spectra
is thoroughly compared to the charge carrier concentration derived from
electrical capacitance-voltage measurements.
