FULL AB-INITIO CALCULATION OF 2ND-ORDER RAMAN-SPECTRA OF SEMICONDUCTORS

We present the first full ab initio calculation of second-order Raman spectra in semiconductors based on density functional perturbation the ory. The method is applied to the Gamma(1)(+) spectra of the elemental semiconductors diamond, silicon, and germanium and reproduces the exp erimental data excellently. Using first-principles phonons, we also ca lculated the corresponding overtone densities of states and Gamma(1)() Raman spectra employing phenomenological polarizability coefficients . Finally, we analyze the results of the different approaches pointing out the relevance of a full first-principles derivation. (C) 1995 Joh n Wiley & Sons, Inc.