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Carlo H.

&. R I P. &. emote. honons. nterface. Pulling strings behind the stage:. ?. Carlo H. Pedro. Massimo. emote nterface honons - History I. Karl 1979: Why is v sat much lower in MOS than in bulk? Maybe we miss some inelastic scattering mech.?.

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Carlo H.

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  1. & R I P & emote honons nterface Pulling strings behind the stage: ? Carlo H. Pedro Massimo

  2. emote nterface honons - History I Karl 1979: Why is vsat much lower in MOS than in bulk? Maybe we miss some inelastic scattering mech.? Karl+Peter 1979: after many lunches together in UIUC cafeteria... q (polar optical phonon) produces macroscopic electric potential: SiO2 Si  P(x') • Fringe fields of oxide phonons scatter electrons in channel • Polar-optical Fröhlich coupling -> strong effect?  Vel-ph u  |x - x'| RIP

  3. eI + eSi 0 wTO2 wRIP2 = eI + eSi    z Vel-ph q-1/2 F dz exp(- q |z|) |yel(z)|2 - - - V - - 1 - 1 F = - eI + eSi eI + eSi  0 Remote Interface Phonons - History II Karl+Peter: after many visits to library (no google, no spinweb, no....) Lucas, Kartheuser & Bardo 1970, Wang & Mahan 1972: • Polar/nonpolar interface produces polar interface phonons: e0: Electronic+ionic D.C. e: Electronic D.C. • The corresponding el-ph interaction decays exponentially away from the interface and is Fröhlich-like:

  4. Remote Interface Phonons - History III • Karl+Peter 1979: SiO2: Static D.C. e0 = 3.9 Electronic D.C. e = 2.5 • VRIP can become relevant in devices • Cannot explain factor 2 in m for Si/SiO2 • Moore+Ferry 1980: • RIP effect on mobility < 10% for MOSFETs  RIP forever? • Fischetti et al 2001: RIP is highly relevant in MOS with high-k insulators! # papers on RIP ~80 citations ~50 citations FNC LKB WM HV MF 70 72 79 80 01

  5. This talk: Role of remote phonon scattering in Si inversion layers with high-k oxides *) Isat vsat Cox (VG-VT) , Cox = eox/tox *) Fischetti, Neumayer, Cartier JAP 90, 4587 (01)

  6. negligible influence on mobility do not scatter electrons directly since orthogonal to single-particle excitations of 2DEG Interface coupled plasmon-phonon modes in Si inversion layers nel Oxide n++ Poly Gate p-Substrate n-channel Gate plasmons Interface phonons (far-side) Interface phonons (RIP) 2DEG plasmons Phonon+plasmon modes: • Dielectric response e(Q,w) in each material • + Laplace equation • + Boundary condition at interfaces

  7. Interface coupled plasmon-phonon modes in the Si/SiO2/Si system Gate-plasmon- like, yet yields strong el+ionic response Phonon-like at small Q, strong ionic response • Scattering strength F(Q,w;z) felt by 2DEG dominated by 2 modes • Both modes are optical, little damping up to large Q • Influence of w2 limited for mobility since hw >> kT

  8. Interface coupled plasmon-phonon modes in the Si/ZrO2/Si system • w2 and w3 have now larger phonon-content • w2 and w3 much lower than in SiO2, therefore more relevant for m • Phonon-plasmon coupling enhances scattering-strength due to antiscreening: |e-1(Q,w2)Vscat| > Vscat for w2wpl

  9. Effective mobility of Si 2DEG Calculate mobility taking into account scattering with... • intravalley, intra+inter-subband acoustic phonons • intra- and inter-subband acoustic phonons • intervalley phonons • coupled plasmon-remote-interface-phonon modes • interface roughness scattering Simplification: triangular well approximation for inversion layer Study mobility... Small VG Low ns High nG High VG High ns Low nG • as a function of SiO2-equivalent gate thickness teq = t e0(ox)/e0(SiO2) • accounting for screening/antiscreening effects of the gate and substrate plasma, as determined by Poisson equation

  10. Thick t, high ns: wRIP low, therefore screening of RIP-scattering by substrate 2D- • plasmons possible m higher • Thick t, low ns: wRIP > w2D-plantiscreening  scattering large m low • Thin t, low ns: large n in gate plasma  screening of RIP by gate plasma, m higher Effective mobility of Si 2DEG: Results Thin Thick • For ZrO2, HfO2, mobility and its ns-dependence completely controlled by RIP modes • and overlap integral.

  11. Gate oxide thickness dependence of 2DEG mobility: Comparison SiO2-ZrO2 Low density: ns = 1.54  1012 cm-3, T = 300 K • Plasma scattering plays little role • Screening effect of gate plasma for thin oxide enhances m

  12. Is there a "future" to Remote Interface Phonon scattering? RIP is likely to become more relevant in nanodevices, such as DGFETs, Wrap-Gate-FETs, Si nanowires,... • more interfaces • less bulk • less doping in channel RIP effect increases It may take less than 20 years to see the next generation of RIP papers... Karl, thanks for everything and all the best to you and Silvia!

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