Quantitative analysis of electronic absorption of phosphorus donors in diamond

Abstract

In this work, phosphorus donors in diamond have been investigated by means of Fourier Transform Infra-Red (FTIR) transmission spectroscopy on a series of fully-characterized homoepitaxial layers. Low-temperature FTIR absorption spectra have been obtained for concentrations of donors in the range ND=3.7×1016–3.5×1018cm−3 and compensating acceptor impurities in the range NA=2.3×1016–3.0×1018cm−3. The absorption spectra is shown to exhibit two peaks at 4220cm−1 and 4540cm−1 corresponding to electronic transitions from the ground state to the 2p0 and 2p± excited states, respectively, of phosphorus donors in the neutral state of charge. The intensity of the most intense peak at 4540cm−1 is found proportional to ND-NA over two decades. The absorption cross-section of the corresponding transition is deduced providing a calibration law for the determination of ND-NA in phosphorus-doped diamond. Furthermore, the linewidth of the peak exhibits a linear variation with the compensating acceptor concentration, interpreted as the effect of the distribution of ionized impurities. The use of the non-destructive and contact-less FTIR optical method is finally discussed to determine the compensation ratio in phosphorus-doped diamond.