Abstract
We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing.
Highlights
Semiconductor nanostructures such as quantum dot superlattices (QD SLs) grown by molecular beam epitaxy (MBE) in the Stranski-Krastanov growth mode offer unique opportunity of engineering their electron and phonon spectra with the most appropriate properties for nanodevices
Raman spectroscopy is considered as the most informative method for determining phonon spectra of semiconductor nanostructures including QD SLs consisting of a variety of materials (Ge/Si, (In,Ga,Al)Sb/GaAs, In(As,Sb)/InP, InAs/(Al,Ga)As) [1-8]
For these structures, according to the Raman selection rules, only longitudinal optical (LO) phonons can be observed in backscattering from the planar surfaces of the SLs while rather sophisticated scattering geometries should be used for probing the transverse optical (TO) phonons [6]
Summary
Semiconductor nanostructures such as quantum dot superlattices (QD SLs) grown by molecular beam epitaxy (MBE) in the Stranski-Krastanov growth mode offer unique opportunity of engineering their electron and phonon spectra with the most appropriate properties for nanodevices. The majority of the reported Raman experiments were carried out for QD SLs grown along the principal crystallographic axis [001] For these structures, according to the Raman selection rules, only longitudinal optical (LO) phonons can be observed in backscattering from the planar surfaces of the SLs while rather sophisticated scattering geometries should be used for probing the transverse optical (TO) phonons [6]. The QD SLs grown on high-index surfaces present significant interest for optoelectronic applications because they reveal intensive narrow linewidth bandgap photoluminescence These structures are much less investigated by Raman spectroscopy despite Raman selection rules allow simultaneous observation of both LO and TO phonons in backscattering experiments from the planar surface. We report the comparison of Raman spectra by acoustic and optical phonons in InAs/AlAs QD SL fabricated on (001) and (311)B GaAs surfaces in the same growth process
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