Two-phonon infrared processes in semiconductors

Abstract. We report our detailed calculation of the infrared spectra of GaAs and GaP from first principles, and similar ongoing efforts for diamond-type spectra, which have recently been calculated. LATTICE DYNAMICS Over the last decade or so, density-functional perturba-tion theory (DFPT) and application of the 2n 1 theo-rem have revolutionized the theoretical study of lattice dynamics [1]. Frozen-phonon algorithms have also been successful in calculating complete phonon dispersion re-lations [2]. These advances allow detailed knowledge of the vibrational continuum, to complement the realistic calculation of electronic band structure that has been pos-sible for some time. Beyond the harmonic approximation, with DFPT it has been possible to calculate anharmonic effects, such as widths, shapes, and shifts of Raman modes [3], an