Phonon-assisted excitonic absorption in diamond

The phonon-assisted optical transitions of excitons in intrinsic diamond have been investigated theoretically and experimentally. Excellent agreement is indicated between absorption spectra measured and calculated based on the phonon coupling strengths from first-principles calculations using just a single adjustable parameter. Temperature shift and broadening are incorporated via a pseudo-Voigt function analysis developed for the derivative of the experimental absorption spectra. The absorption coefficients of excitons in discrete and continuum states are separated and contributions from different phonon modes are discussed, which enable theoretical derivation of the exceptionally high phonon-assisted radiative rate of excitons in diamond among indirect-gap semiconductors. This study expands the applicability of the second-order perturbation theory involving electron-phonon interactions in materials important for future photonics and power electronics.