Abstract
Polarized far infrared reflectance has been measured at oblique incidence for 11 ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}\mathrm{P}$ superlattices grown lattice matched on InP(100) wafers by chemical beam epitaxy. Both the alloy layer thickness (0.25--20 nm) and number of periods (10--40) were varied. The spectra contained sharp reflectance peaks at the frequencies of the vertically propagating, zone-center, transverse optical (TO), and longitudinal (LO) optical phonons. The contributions of the individual phonon modes of the alloy layers were resolved using a generalized analysis procedure including GaAs-like, disorder induced, and InAs-like LO and TO phonons. A nonlinear variation of the alloy LO phonon frequencies with layer thickness was observed arising from phonon confinement in the alloy layers. From this result, the LO phonon in bulk InAs is predicted to exhibit anomalous dispersion. On both sides of the alloy layers we observed 0.6-nm-thick interface layers of significantly different alloy composition. Surprisingly for a lattice matched system, the InP layers exhibit a slight strain arising from the interface formation.
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