Phonon Raman scattering in quantum wires (original) (raw)
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Raman scattering from confined phonons in GaAs/AlGaAs quantum wires
Superlattices and Microstructures, 1998
We report on photoluminescence and Raman scattering performed at low temperature (T = 10 K) on GaAs/Al 0.3 Ga 0.7 As quantum-well wires with effective wire widths of L = 100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at ω L10 = 285.6 cm −1 for L = 11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderlein † as applied to the GaAs/Al 0.3 Ga 0.7 As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques.
Applied Physics A, 2006
Raman scattering is shown to be an effective probe of optical and surface optical phonons in highly crystalline semiconducting nanowires (SNWs). We show that the confinement model of Richter et al. well describes the nanowire diameter dependence of the asymmetric broadening of the onephonon band in Si nanowires observed at ∼ 520 cm −1. We also show that the use of high laser flux (∼ 0.1 mW/µm 2) leads to a second mechanism that can asymmetrically broaden the 520 cm −1 Raman band. This broadening has nothing to do with confinement, and can qualitatively be understood in terms of inhomogeneous laser heating. A model is presented that supports this explanation. The production of SNWs via the vapor-liquidsolid growth mechanism leads, in many cases, to an instability in the nanowire diameter or cross-sectional area. In the second part of this review, we show that this instability activates the surface optical (SO) phonon Raman scattering. Examples of this phenomenon are shown for GaP and ZnS nanowires. The former and latter have, respectively, cylindrical and rectangular cross sections. We show that the cross-sectional shape of the nanowire is important for a quantitative analysis of these SO modes.
Electron intersubband scattering by confined and localized phonons in real quantum wires
Journal of Physics: Condensed Matter, 1992
AbstracL "e present study deals with electron intersubband scattering in real quanlum wire slrudures. Both the multi-subband SVUcture and mnfined phonon modes are mnsidered together. 'lle rates of scattering by mnRned longitudinaloptical (W) phonons and by surfaceoptieal (so) phonons are calculated lalting into account all possible W phonon modes as well as all posible elenmn intersubband lransilions. The estimations of Vansition rates for GaAs/ALAs awls have shown that inuasubband electron scattering and mmt intersubtend Vansitions are due primarily lo scattering by mn6aed w phonons, but in-"ant intenubbaod Lransitions the mntribution of so phonons may be dominant when lhe phonon energy is close lo lhe intersubtend energy separation. Moreover, electron7so-phonon scattering might play an impartant pan in kwtemperature elenron lransport beguse the GaAsIike so mode is shifted towanis lower frequencies mmpared with that of U) phonons. ?he energy dependence of the tolal scattering rate in an ideal quantum wire ahibils multiple sharp peaks related lo each intersubband Vansition. These peaks originate f " the m n a n t nature of lhe density of slates in ideal onedimensional systems. It is demonstrated lhat in real quantum wires with variable thickness the m n a n t peaks broaden or even disappear due lo variation of subtend energies.
Phonon spectra in quantum wires
Hemijska Industrija, 2007
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Raman-active phonon line profiles in semiconducting nanowires
Vibrational Spectroscopy, 2006
Results of Raman scattering investigations of optical phonons confined in the cross section of small diameter Si nanowires are discussed. Using low excitation intensity at 514.53 nm to study Si as a prototypical material, we first demonstrate that the outcome of the phonon confinement is an asymmetric broadening and downshifting of the LO-TO phonon line observed at 520 cm À1 in the bulk. The effect is important in Si wires with diameter d < 10 nm. We find good agreement between our data and an early theory due to Richter et al., provided we introduce an additional factor that sets the phonon confinement length. Furthermore, we examine the effects on the 520 cm À1 lineshape from increasing the laser power density in the tight microRaman focal spot size ($1 mm). We find that a second asymmetric line broadening mechanism is also present that can be identified with an inhomogeneous temperature distribution set up in the nanowires. This distribution is driven by the Gaussian spatial intensity of the laser beam in the focal plane of the microRaman instrument. Using the thermal properties of the phonons in Si, we can explain semi-quantitatively the complex changes in the lineshape that we observe in both small and large diameter Si nanowires, i.e., with or without phonon confinement as an active consideration.
Acoustic-phonon scattering in a rectangular quantum wire
Physical Review B, 1993
The rates of electron scattering by acoustic phonons in a rectangular quantum wire embedded into another material are calculated in the framework of the Fermi golden rule. Both intrasubband and intersubband electron scattering by acoustic phonons are considered. It has been shown that due to uncertainty of momentum conservation in quasi-one-dimensional systems the acoustic-phonon scattering becomes essentially inelastic in contrast to that in bulk materials. The acoustic-phonon scattering rate in quantum wires increases with the decrease of cross section of the wire and is much greater than that in bulk materials. It is shown that the correct treatment of inelasticity leads to a nonmonotonic dependence of the emission rate on electron energy and to the disappearance of the divergency of the acoustic-phonon scattering rate at the bottom of each subband. Therefore, the scattering time averaged over the distribution function exceeds considerably that calculated using elastic and quasielastic approaches where the scattering rate is divergent. We demonstrate that electron mobility at temperatures less than 100 K calculated within elastic or quasielastic approximations is greatly underestimated.
Communications in Physics, 2015
Within the framework of the macroscopic dielectric continuum model the longitudinal optical (LO) phonon modes are derived for a cylindrical semiconductor quantum wire made of semiconductor 1 (well material) embedded in another finite semiconductor 2 (barrier material). The phonon states of modes are given by solving the generalized Born-Huang equation. It is shown that there may exist four types of longitudinal optical phonon modes according to the concrete materials forming the wire. The dispersion equations for phonon frequencies with wave-vector components parallel to the wire are obtained. After having quantized the phonon field we derive the Fröhlich Hamiltonian describing the electron--LO-phonon interaction. The influence of the thickness of the barrier layer as well as the thin metallic shell on the phonon frequencies and their interaction with electrons is studied.
Journal of the Korean Physical Society, 2013
We investigate the influence of phonon confinement on the optically-detected electrophonon resonance (ODEPR) effect and ODEPR linewidth in rectangular quantum wires (RQW). The ODEPR conditions as functions of the wire's size and the photon energy are also obtained. The splittings of ODEPR peaks caused by the confined phonon are discussed. The numerical result for a specific RQW shows that in the two cases of confined and bulk phonons, the linewidth decreases with increasing wire size and increases with increasing temperature. Furthermore, in the small range of the wire's size (L ≤ 40 nm), phonon confinement plays an important role and cannot be neglected in reaching the ODEPR linewidth.
On the Raman scattering from semiconducting nanowires
Journal of Raman Spectroscopy, 2007
We present a short review of recent work on the unusual Raman scattering characteristics in semiconductor nanowires, focusing on the dependence of the intensity, spectral and spatial character of the scattering response on the size, shape and composition of the nanowires. Results of Raman scattering collected from individual Si and nanowires and nanocones indicate that the observed enhancement is dependent on the diameter (d), the excitation wavelength (l laser) and the incident polarization state. Strong agreement between experimental data and model calculations of scattering from an infinite dielectric cylinder is found. This size dependence is in accordance with other recent findings in which a diameter-dependent dipolar 'antenna' pattern for the scattered intensity and a cross-sectional shape dependence of the surface optic (SO) phonon dispersions were seen. Further providing evidence of the nanowire shape and size dependence on Raman scattering, these results suggest manipulation of classical electromagnetic scattering signatures, thereby expanding opportunities for engineering the photonic and sensing properties of nanowires.
Mobility of 1-D GaAs Quantum Wire Limited by Polar Optic Phonon Scattering
The polar optical phonon (POP) scattering limited mobility in 1-DEG quantum wire of GaAs has been investigated. The variation of mobility with well width for 1D GaAs quantum wire has been studied. The mobility dependence on the transverse dimension of quantum wire for different values of electron energy has been also been investigated. The results obtained at 300K for GaAs wire reveal that the variation is almost linear in nature.