Phonons in InAs Quantum Dot Structures
|Alexander G. Milekhin 1, Alexander I. Toropov 1, Dietrich RT Zahn 2|
1. Institute of Semiconductor Physics SB RAS, Lavrentjeva 13, Novosibirsk 630090, Russian Federation
We present a Raman study of the phonon spectra of periodical structures with (In,Ga)As QDs in (Al,Ga)As matrix as well as AlAs QDs embedded in InAs.
The nanostructures studied were grown by molecular beam epitaxy in the Stranski-Krastanov growth mode on (001)-oriented GaAs substrates.
Low frequency resonant Raman scattering by acoustic phonons was observed in the QD structures. The periodic oscillations seen in the Raman spectra are well described by the elastic continuum model.
Raman scattering by confined TO and LO phonons was observed in both in InAs and AlAs QDs. Optical phonons of QDs are strongly affected by both strain and confinement. The Raman study reveals a two-mode behavior of optical phonons in the whole composition range for both InGaAs QDs and the AlGaAs matrix.
With increasing excitation energy (from 1.8 to 2.4 eV) a red shift of InAs and GaAs-like LO phonons in InGaAs QDs is observed which is explained by selective resonant Raman scattering.
Interface InAs- and GaAs-like phonons as well as AlAs- and GaAs-like phonons were observed in InGaAs QDs and the AlGaAs matrix, respectively. Their frequency positions were analyzed as a function of the alloy content within the dielectric continuum model. The positions of IF phonons in the QD structures observed in the experiment agree well with calculated ones assuming the QDs have a shape of oblate ellipsoids.
In the vicinity with E0 resonance in QDs, up to third-order scattering is observed, involving both pure overtones of the first-order InAs, GaAs and AlAs optical and interface phonons and combination of phonons from the materials. Possible mechanisms of these processes are discussed.
Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium J, by Alexander G. Milekhin
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-26 07:36 Revised: 2009-06-07 00:48