Phonon dispersion curves of GaAs/AlAs superlattices (original) (raw)

Phonon dispersion curves of GaAs-AlAs superlattices grown in the [111] and [110] directions

Physical Review B, 1989

The phonon properties of (GaAs),(AlAs), superlattices are studied with an eleven-parameter rigid-ion model. Short-range interactions up to the second neighbours are included, and the long-range Coulomb interaction is calculated exactly. Modes propagating both normal (k/l = 0) and oblique (k/l # 0) to the interfaces are studied. Anisotropy of sane center optical phononu is examined. The theoretical results are compared with the existing experimental data with favorable agreement .

Confined longitudinal and transverse phonons in GaAs/AlAs superlattices

Superlattices and Microstructures, 1986

The phonon spectrum of GaAs/AIAs superlattices along the (001) growth direction is calculated using a new approach based on a realistic unified treatment of the interactions in both bulk constituents, which naturally lends itself to dealing with superlattice geometries. Results for a (GaAs)3(AIAs)3 superlattice are shown with emphasis on different aspects of confinement.

Phonon spectra of ultrathin GaAs/AlAs superlattices: An ab initio calculation

Phonon spectra of ultrathin (GaAs), (A1As)"(001) superlattices are studied theoretically using linear-response density-functional techniques. Results are presented for n 1,2, 3 superlattices, along with prototype superce11 calculations aimed at simulating a completely disordered (alloy) as well as some partially disordered superlattices. Besides interfacial disorder, which modifies the effective confinement length of low-order longitudinal-optic phonons, we find thatin the ultrathin regimesome degree of cationic mixing must also affect inner planes in order to explain experimental findings. ' This is so becausein a two-mode alloy such as GaAlAsthe Ga(Al) ions do not participate in the vibration of A1As-(GaAs-) like modes, and therefore give no contribution to the corresponding polarization.

Phonon properties of GaAs/AlAs superlattice grown along the [110] direction

Physical Review B, 1989

We report Raman scattering studies of GaAs/A1As superlattices grown along the [110]direction. The appearance of distinct x-ray satellite peaks around the Bragg reflections demonstrates the formation of highly ordered periodic superlattice structures. The confined-optical-phonon modes corresponding to the three optical bulk branches as well as the folded-acoustic-phonon modes are observed. The confined modes have frequencies which map closely onto those of the optical phonons of the parent materials in the [110]direction (I-K-X) of k space. We also observe resonant Raman scattering by confined-optical and in-plane (interfacelike) vibrational overtones and their combinations. The results of a lattice-dynamical calculation for this superlattice is also presented with special emphasis on angular dispersion and the mixed polarization of superlattice modes.

Phonon properties of (311) GaAs/AlAs superlattices

Physical Review B, 1994

Raman scattering spectra of GaAs/AIAs superlattices grown along the [311] direction are compared with results of lattice-dynamical calculations. Confined optical as well as folded acousticphonon modes are clearly observed at frequencies in excellent agreement with those predicted. Several of the bulk branches hybridize along the low-symmetry [311] direction, producing confined optical modes in the superlattice of mixed longitudinal/transverse character. This hybridization complicates also the assignment of a mode order to the con6ned phonons, since they encompass components deriving from several bulk branches with different effective wave vectors. We demonstrate that a proper assignment can only be made by comparison to the calculated eigenvector envelope functions. We discuss how the crystal symmetry affects the angular dispersion of the optic modes.

Phonons in GaAs/AlAs superlattices grown along the [111] direction

Physical Review B, 1990

We present Raman-scattering data for GaAs/AlAs superlattices grown on GaAs substrates along the [111]direction. The appearance of distinct x-ray satellite peaks around the Bragg reflections demonstrates the formation of highly ordered periodic superlattice structures. The confined optical-phonon modes have frequencies which map closely those of the parent materials in the [111] direction of k space. We also observe folded acoustic-phonon modes. The results of a latticedynamical calculation for these superlattices on the basis of the shell model are presented, with special emphasis on the angular dispersion of "interface" modes.

Phonons in semiconductor superlattices

Superlattices and Microstructures, 1991

We present theoretical studies of phonon modes in semiconductor superlattices in a rigid-ion model. We examine the dispersion curves for phonone propagating in any directions, taking into account the long-range Coulomb interaction. We introduce an alternative approach which avoids direct computation of the Coulomb interaction in superlattices.

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

International Journal of Infrared and Millimeter Waves, 1990

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/AlxGa1−xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.

Phonon modes of short-period (GaAs)n/(AlAs)n superlattices

2002

In the work finding optical phonon energies from photoluminescence spectra and interpretation of their dependence on quantum well width are carried out. Remarkable decreasing both GaAs and AlAs phonon energies has been observed. It is shown that this dependence differs noticeably from that obtained from Raman spectra. The possible origin of this phenomenon is considered.  2002 Published by Elsevier Science B.V. PACS: 78.66.-w; 78.55.Cr; 63.22.+m Keywords: Short-period superlattice; Photoluminescence; Longitudinal optical phonon; Confined mode; Γ -X transfer 0375-9601/02/$ -see front matter  2002 Published by Elsevier Science B.V. PII: S 0 3 7 5 -9 6 0 1 ( 0 2 ) 0 0 0 1 6 -6

Optical phonon damping in the ultrathin-layer GaAs/AlAs superlattices

Superlattices and Microstructures, 1999

We performed the precision measurements of the near-normal far-infrared reflection and transmission spectra of the MBE-grown (GaAs) n /(AlAs) n (n = 1, 2, 4) superlattices. The results obtained show a noticeable (almost twofold) increase in the AlAs-phonon damping when n is decreased from 4 to 1. We consider possible physical mechanisms of this increase and compare our results with those obtained by other authors. The main implication of the work is that the increase in the TO-phonon damping may be related to interface broadening whose role becomes more important when the superlattice period decreases.