CORE X-RAY-SPECTRA IN SEMICONDUCTORS AND THE MAHAN-NOZIERES-DE-DOMINICIS MODEL

The Mahan-Nozieres-De Dominicis (MND) model of core x-ray spectra is e xamined for semiconductors. Due to the finite band gap, the Anderson o rthogonality does not occur, and thus spectra near the band edge can b e calculated without the shakeup contribution. For semiconductors, and not only for metals, we investigate whether the remaining many-partic le dynamic exchange effect of the MND model, or so-called replacement. can significantly alter x-ray spectral shapes near the band edge from those obtained from a straightforward final-state rule. For both emis sion and absorption, in the absence of shakeup, an exact formulation s uitable for materials with band structure is discussed. A numerical mo del for a semiconductor with a 1-eV band gap demonstrates the band-edg e modifications, and shows a 50% effect at the band edge, indicating t hat this dynamic exchange effect can be significant and should be cons idered in any specific emission or absorption calculation for a semico nductor. Although the ineffectiveness of the orthogonality theorem in semiconductors is emphasized, a suppression near the band edge also re mains a possibility. included is a discussion on the breakdown of the final-state rule. In addition, connection is made to the determinantal approach of Ohtaka and Tanabe. [S0163-1829(98)01040-6].