Accurate FTIR determination of boron concentration in CVD homoepitaxial diamond layers

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.