The variation of optical absorption of CVD diamond as a function of temperature

The infrared absorption of CVD diamond films is reported as a function of temperature in both intrinsic and boron-doped samples. In pure diamond, because of the inversion symmetry of the lattice, there is no one-phonon IR absorption, but there are bands corresponding to the interaction of the photon with two or more phonons. We fit the measured temperature dependence of the absorption by including the Bose-Einstein factors for the two phonons involved at each energy. The infrared absorption of boron was measured in the range 500-5000 cm between 14 and 630 K. We show that the temperature dependence of the absorption can be understood in terms of thermal ionisation and thermal transitions between electronic states. © 2001 Elsevier Science B.V. All rights reserved.