Dr Paul Kinsler.
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<> From eenpk@sun Mon Oct 6 17:07:28 1997
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<> From: P Kinsler
<> Message-Id: <29747.9710061619@sun.leeds.ac.uk>
<> Subject: confined phonon modes (fwd)
<> To: eenpk
<> Date: Mon, 6 Oct 1997 17:19:56 +0100 (BST)
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<> Forwarded message:
<> >From een6rwk Mon Oct 6 17:14 BST 1997
<> From: R W Kelsall
<> Date: Mon, 6 Oct 97 17:14:40 BST
<> Message-Id: <29652.9710061614@sun.leeds.ac.uk>
<> To: eenpk
<> Subject: confined phonon modes
<> Content-Type: text
<> Content-Length: 15930
<>
<> Paul;
<>
<> some papers from BIDS which may be worth following up. No. 5 looks particularly interesting.
<>
<> Rob
<>
<>
<>
<>
<>
<> (1) TI: SIMPLIFIED MICROSCOPIC MODEL FOR ELECTRON OPTICAL-PHONON
<> INTERACTIONS IN QUANTUM-WELLS
<> AU: BHATT_AR, KIM_KW, STROSCIO_MA, HIGMAN_JM
<> NA: N CAROLINA STATE UNIV,DEPT ELECT & COMP ENGN,RALEIGH,NC,27695
<> USA,RES OFF,RES TRIANGLE PK,NC,27709
<> UNIV ILLINOIS,BECKMAN INST,URBANA,IL,61801
<> JN: PHYSICAL REVIEW B-CONDENSED MATTER, 1993, Vol.48, No.19,
<> pp.14671-14674
<> IS: 0163-1829
<> DT: Note
<> AB: A simplified microscopic model of optical phonons in
<> dimensionally confined structures is formulated and applied to
<> calculate electron-optical-phonon scattering rates in GaAs/AlAs
<> quantum wells. For this simplified model which circumvents
<> performing a complicated ab initio calculation of the force
<> constants at the interface, it is demonstrated that the
<> resulting dispersion relation and scattering rates for
<> electron-optical-phonon interactions agree very well with those
<> obtained from detailed ab initio studies. It is also shown that
<> for GaAs/A]As structures, the macroscopic dielectric continuum
<> model provides a good approximation to the scattering rate
<> predicted by the microscopic models.
<> KP: ZINCBLENDE STRUCTURE COMPOUNDS, LATTICE-DYNAMICS, GAAS/ALAS
<> SUPERLATTICES, FORCE-CONSTANTS, HETEROSTRUCTURES, GAAS,
<> POLARIZABILITY, SCATTERING, SYSTEMS
<>
<>
<> (3) TI: HOT-ELECTRON RELAXATION VIA THE EMISSION OF GAAS OPTICAL MODES
<> AND ALAS INTERFACE MODES IN GAAS ALAS MULTIQUANTUM WELLS
<> AU: OZTURK_E, CONSTANTINOU_NC, STRAW_A, BALKAN_N, RIDLEY_BK,
<> RITCHIE_DA, LINFIELD_EH, CHURCHILL_AC, JONES_GAC
<> NA: UNIV ESSEX,DEPT PHYS,COLCHESTER CO4 3SQ,ESSEX,ENGLAND
<> UNIV CAMBRIDGE,CAVENDISH LAB,CAMBRIDGE CB3 0HE,ENGLAND
<> JN: SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 1994, Vol.9, No.5 SS,
<> pp.782-785
<> IS: 0268-1242
<> AB: We demonstrate via hot-electron photoluminescence and high-
<> temperature mobility measurements the importance of the AlAs
<> interface mode in the energy relaxation of electrons in
<> GaAs/AlAs multi-quantum wells. A corresponding investigation of
<> a similar GaAs/Al0.24Ga0.76As system illustrates that this is
<> not the case for AlGaAs barrier devices where GaAs modes are
<> the dominant energy relaxation process. The importance of the
<> AlAs interface mode is not simply related to its intrinsic
<> scattering rate but also to its shorter lifetime (compared with
<> GaAs modes). Hot-phonon effects are therefore crucial to a full
<> understanding of the experimental data.
<> KP: DOUBLE HETEROSTRUCTURES, PHONON INTERACTIONS, TRANSPORT
<>
<> (4) TI: ENERGY AND MOMENTUM RELAXATION RATES FOR CONFINED AND INTERFACE
<> MODES IN QUANTUM-WELL STRUCTURES
<> AU: GUPTA_R, RIDLEY_BK
<> NA: UNIV ESSEX,DEPT PHYS,WIVENHOE PK,COLCHESTER CO4
<> 3SQ,ESSEX,ENGLAND
<> JN: SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 1994, Vol.9, No.5 SS,
<> pp.753-755
<> IS: 0268-1242
<> AB: In GaAs/AlAs quantum well structures both the confined GaAs
<> optic phonon and the AlAs interface polariton (IP) mode
<> contribute to the energy and momentum relaxation of hot
<> electrons. It has been shown that in real multiple quantum well
<> structures elastic scattering of phonons can lead to a non-
<> drifting population of hot phonons, which results in a
<> suppression of the high-field electron drift velocity. The
<> consequences for device application are obvious. The non-drift
<> of the mode is determined by the relative magnitudes of its
<> energy and momentum relaxation rates.
<> We present a calculation of the lifetime and the elastic
<> scattering rates for confined and interface modes in GaAs/AlAs
<> quantum wells. It is found that the decay rates of the two
<> modes exhibit different well-width dependences, and that
<> scattering from interface roughness is the dominant mechanism
<> for momentum relaxation. The implications for high-field
<> transport are discussed.
<> KP: SCATTERING
<>
<> (5) TI: ELECTRON-PHONON SCATTERING IN GA1-XALXAS QUANTUM-WELL
<> STRUCTURES IN AN ELECTRIC-FIELD
<> AU: ZHU_JL, DUAN_WH, GU_BL
<> NA: TSING HUA UNIV,DEPT PHYS,BEIJING 100084,PEOPLES R CHINA
<> CHINESE CTR ADV SCI & TECHNOL,WORLD LAB,CTR THEORET
<> PHYS,BEIJING 100080,PEOPLES R CHINA
<> CENT IRON & STEEL RES INST,BEIJING 100081,PEOPLES R CHINA
<> JN: PHYSICAL REVIEW B-CONDENSED MATTER, 1994, Vol.50, No.8,
<> pp.5473-5479
<> IS: 0163-1829
<> AB: Effects of the well width and an electric field on electron-
<> phonon scattering are studied for two kinds of quantum-well
<> structures. One is a symmetrical single quantum well (SSQW)
<> Ga0.6Al0.4As/GaAs/Ga0.6Al0.4As, and the other is an
<> asymmetrical single quantum well (ASQW) Ga0.6Al0.4As/GaAs-
<> Ga0.8Al0.2As/Ga0.6Al0.4As. Calculated results reveal that for
<> both structures without an electric field, the intrasubband and
<> intersubband scattering rates due to interface phonons,
<> respectively, decrease and increase with increasing well width
<> while those due to confined phonons increase with increasing
<> well width. It is found that the difference between SSQW and
<> ASQW structures results in a significant change of phonon modes
<> and electronic structure and consequently the dependence of
<> scattering rates on an applied electric field is quite
<> different for the two structures, and that the intersubband
<> scattering rates can be considerably changed by applied
<> electric field as the well width is large. The result would be
<> useful for analyzing experimental results and designing some
<> devices in the future.
<> KP: PHOTOCURRENT SPECTROSCOPY, CONFINED LO, GAAS, EXCITONS,
<> HETEROSTRUCTURES, POLARIZABILITY, SUPERLATTICES, VIBRATIONS,
<> MODEL, RATES
<>
<> (6) TI: PHONON-SCATTERING SUPPRESSION IN SHORT PERIODIC ALAS/GAAS
<> MULTIPLE-QUANTUM-WELL STRUCTURES
<> AU: LETRAN_TT, SCHAFF_WJ, RIDLEY_BK, CHEN_YP, CLARK_A, EASTMAN_LF
<> NA: CORNELL UNIV,SCH ELECT ENGN,PHILLIPS HALL,ITHACA,NY,14853
<> JN: JOURNAL OF APPLIED PHYSICS, 1994, Vol.75, No.7, pp.3491-3499
<> IS: 0021-8979
<> AB: The suppression of longitudinally polarized optical-phonon
<> (LOP) electron scattering in multiple quantum wells (MQWs) was
<> sought in short periodic AlAs/GaAs with well widths of 12, 15,
<> and 20 monolayers and AlAs barrier widths of 2 and 4
<> monolayers, based on a study of electron mobility in the plane
<> of the MQW. Two-dimensional electron-gas structures with MQWs
<> of up to eight wells in their channel were grown. Their
<> mobilities at room temperature were slightly reduced, as
<> compared to samples without MQW channel, due to interaction
<> with interface polaritons from AlAs barriers, while mobility at
<> temperatures < 50 K improved due to reduction of remote ionized
<> impurity scattering. The theoretical analysis of the results
<> based on the model of hybridon-electron interaction in an
<> infinite superlattice is presented. The reduction of room-
<> temperature mobility in the MQWs is believed to be caused by
<> the interaction of electrons with both barrier interface-
<> polariton (IP) -like modes and the well LOP-IP hybrids. An
<> alternative explanation of the results of a similar experiment
<> done elsewhere is offered denying the evidence of strong
<> suppression of LOP scattering there.
<> KP: OPTICAL PHONONS, SUPERLATTICES, MOBILITY
<>
<>
<>
<>
<>
<> (12) TI: INTERACTION BETWEEN AN ELECTRON AND OPTICAL PHONONS IN POLAR
<> SEMICONDUCTOR HETEROSTRUCTURES
<> AU: SHI_JJ, PAN_SH, LIU_ZX
<> NA: CHINA CTR ADV SCI & TECHNOL,WORLD LAB,POB 8730,BEIJING
<> 100080,PEOPLES R CHINA
<> HENAN NORMAL UNIV,DEPT PHYS,XINXIANG 453002,PEOPLES R CHINA
<> CHINESE ACAD SCI,INST PHYS,BEIJING 100080,PEOPLES R CHINA
<> JN: ZEITSCHRIFT FUR PHYSIK B-CONDENSED MATTER, 1996, Vol.100, No.3,
<> pp.353-364
<> IS: 0722-3277
<> AB: Interface phonons and bulk-like longitudinal-optical (LO)
<> phonons and their interaction with an electron are studied for
<> a finite four-layer heterostructure (FFLHS). An analysis of the
<> field eigenvectors shows that, in the vicinity of the
<> Brillouin-zone center, an interface transverse-optical (TO)
<> mode oscillates at the bulk LO frequency, and an interface LO
<> mode oscillates at the bulk TO frequency. Analytic expressions
<> and numerical illustrations for dispersion relations of
<> interface modes and for electron-phonon coupling functions and
<> scattering rates are obtained for finite, semi-infinite and
<> infinite quantum well (QW) structures which are important
<> special cases of an FFLHS. It is shown that the scattering
<> rates depend strongly on the well width of a QW structure, and
<> that interface modes are much more important than bulk LO modes
<> when the well width is small. The calculated results also show
<> that the usual selection rules for intersubband and
<> intrasubband transitions break down in asymmetric
<> heterostructures. Moreover, we have found an interesting
<> result. That is, in comparison with the negligibly small
<> interaction between an electron and the lowest-frequency
<> interface-mode in symmetric single QWs and commonly used step
<> QWs, this interaction may be very large in asymmetric single
<> QWs and general step QWs.
<> KP: QUANTUM-WELLS, COLLECTIVE EXCITATIONS, SCATTERING RATES,
<> DIELECTRIC SLAB, LO PHONONS, INTERFACE, MODES, SUPERLATTICES,
<> CRYSTALS, HETEROJUNCTIONS
<>
<> (13) TI: Electron capture in quantum wells via scattering by electrons,
<> holes, and optical phonons
<> AU: Kalna_K, Mosko_M
<> NA: SLOVAK ACAD SCI,INST ELECT ENGN,DUBRAVSKA CESTA 9,SK-84239
<> BRATISLAVA,SLOVAKIA
<> JN: PHYSICAL REVIEW B-CONDENSED MATTER, 1996, Vol.54, No.24,
<> pp.17730-17737
<> IS: 0163-1829
<> AB: Electron-capture times due td the electron-electron (e-e),
<> electron-hole (e-h), and electron-polar optical phonon (e-pop)
<> interactions are calculated in the GaAs quantum well (QW) with
<> electron and hole densities 10(11) cm(-2). The calculated
<> capture times oscillate as a function of the QW width with the
<> same period but with different amplitudes. The e-h capture time
<> is two to four orders larger and the e-e capture time one to
<> three orders larger than the e-pop capture time. The exceptions
<> are the QW widths near resonance minima, where the e-e capture
<> time is only 2-3 times larger and the e-h capture time 10-100
<> times larger. A different physical origin of the oscillatory
<> behavior is demonstrated for the e-e and e-pop capture times.
<> Effects of exchange and degeneracy on the e-e capture are
<> analyzed. The exchange effect increases the e-e capture time
<> approximately two times while the degeneracy does not change
<> the capture time except for the QW depths and widths near the
<> resonance.
<> KP: CARRIER-CARRIER SCATTERING, MONTE-CARLO, GAAS, HETEROSTRUCTURES,
<> THERMALIZATION, LASERS, PLASMA
<>
<> (14) TI: Electron scattering by optical phonons in AlxGa1-
<> xAs/GaAs/AlxGa1-xAs quantum wells
<> AU: Zianni_X, Simserides_CD, Triberis_GP
<> NA: UNIV ATHENS,DEPT PHYS,SECT SOLID STATE PHYS,ZOGRAFOS
<> 15784,ATHENS,GREECE
<> JN: PHYSICAL REVIEW B-CONDENSED MATTER, 1997, Vol.55, No.24,
<> pp.16324-16330
<> IS: 0163-1829
<> AB: The scattering of a quasi two-dimensional electron gas by
<> optical phonons in selectively doped AlxGa1-xAs/GaAs/AlxGa1-xAs
<> quantum wells is systematically studied in order to determine
<> the effect of phonon confinement. The electron states are
<> calculated solving self-consistently Schrodinger and Poisson
<> equations to obtain an accurate dependence upon the structure
<> parameters and the temperature. We study the way the scattering
<> is affected by the form of the phonons calculating the mobility
<> using three models for the phonons. They are considered: (a) as
<> three dimensional (3D), (b) as a set of confined and interface
<> phonons, and (c) as the normal modes of the heterostructure.
<> The relaxation times for the electron energy subbands are
<> calculated solving the system of Boltzmann equations. The
<> effect of the temperature and the well width variation is also
<> investigated. The results are in a good agreement with
<> experimental measurements. The agreement is only slightly
<> dependent on the model used for the phonons and becomes best
<> when the effect of the heterostructure on the phonon modes is
<> taken into account.
<> KP: HETEROSTRUCTURES, MODULATION, MOBILITY
<>
<> (15) TI: Polar optical modes in semiconductor nanostructures
<> AU: Velasco_VR, GarciaMoliner_F
<> NA: CSIC,INST CIENCIA MAT,E-28049 MADRID,SPAIN
<> UNIV JAUME I,CATEDRA CIENCIA CONTEMPORANEA,CASTELLO DE PLANA
<> 12071,SPAIN
<> JN: SURFACE SCIENCE REPORTS, 1997, Vol.28, No.5-6, pp.125-176
<> IS: 0167-5729
<> DT: Review
<> AB: Polar optical modes play an important role in electron-phonon
<> processes such as scattering rates, polaron effects and
<> resonant Raman scattering in quantum wells and superlattices,
<> Because of this there has been in recent years a strong
<> interest in the development of a long-wave theory for optical
<> modes in semiconductor nanostructures. This theory would be the
<> equivalent of the effective mass theory for electrons. Besides
<> microscopic calculations it should provide a satisfactory
<> theoretical model to study the long-wave limit, to which most
<> experimental evidence is circumscribed. Important elements in
<> this type of theory are the inclusion of the bulk spatial
<> dispersion of the optical modes together with the fact that, at
<> an interface between two media, mechanical and electromagnetic
<> boundary conditions must be satisfied, In some cases, like
<> InAs/GaSb and related superlattices, the details of the
<> interface structure are also important. We discuss here the
<> different approaches employed to study the long-wave limit in
<> these systems, including other approaches in which the envelope
<> function model is derived directly from microscopic lattice
<> dynamics.
<> KP: ELECTRON-PHONON INTERACTION, GAAS-ALAS SUPERLATTICES, ENERGY-
<> LOSS SPECTRUM, PLANAR VIBRATIONAL-MODES, RECTANGULAR QUANTUM
<> WIRE, RAMAN-SCATTERING, GAAS/ALAS SUPERLATTICES, CONFINED LO,
<> INTERFACE MODES, RESONANT RAMAN
<> WA: phonons, heterostructures, quantum wells, superlattices
<>
<>
<>
<> **** End of Data ****
<>
<>
<> ----- End Included Message -----
<>
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