Optical transitions in strained Ge/Si superlattices

U. Schmid, J. Humlíček, F. Lukeš, M. Cardona, H. Presting, H. Kibbel, E. Kasper, K. Eberl, W. Wegscheider, G. Abstreiter

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

We present spectroellipsometric measurements of the linear optical response of ultrathin Ge/Si strained-layer superlattices (SLSs) grown by molecular beam epitaxy with varying strain state and periodicity. The experiments were performed at 300 K in the energy range 1.6-5.7 eV. As predicted from ab initio calculations, the E1 transitions of the bulk split into various components in the SLSs. From the fitted critical point (CP) energy of the most pronounced of these components, the composition of the SLSs can be estimated. Compared with alloys of the same composition, the onset of the absorption in the SLSs is shifted towards lower energies than in compositionally equivalent alloys. The E2 transitions can be fitted to two CPs. Both exhibit a shift due to the hydrostatic component associated with the internal strain that is about one-half of what would be expected from bulk properties. We also present evidence of confinement effects.

Original languageEnglish
Pages (from-to)246-250
Number of pages5
JournalThin Solid Films
Volume222
Issue number1-2
DOIs
StatePublished - 20 Dec 1992

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