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On the Genesis of Ge/Si Epitaxial Interfaces: Tracking the Behavior of Deposited Atoms

On the Genesis of Ge/Si Epitaxial Interfaces: Tracking the Behavior of Deposited Atoms using Molecular Dynamics with Analytic Bond Order Potentials. Interface growth: LEEM and XPEEM. Empirical molecular dynamics: macroscopic relevance vs. BOP. Atom deposition: specialities and results.

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On the Genesis of Ge/Si Epitaxial Interfaces: Tracking the Behavior of Deposited Atoms

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  1. On the Genesis of Ge/Si Epitaxial Interfaces: Tracking the Behavior of Deposited Atoms using Molecular Dynamics with Analytic Bond Order Potentials Interface growth: LEEM and XPEEM Empirical molecular dynamics: macroscopic relevance vs. BOP Atom deposition: specialities and results Kurt Scheerschmidt#, Oussama Moutanabbir* #Max Planck Institute of Microstructure Physics, Halle/Saale, Germany *Dep. of Engineering, Ecole Polytechnique de Montreal, Montreal, Quebec, Canada schee@mpi-halle.dehttp://www.mpi-halle.de

  2. LEEM and XPEEM (a) Ge 3d to Si 2p intensity ratios as a function of Ge coverage. Solid line: calculated values for an abrupt Ge/Si interface; dots: growth experiment. (b) Evolution of dR as a function of Ge coverage at growth temperature of 200 °C (squares) and 270 °C (circles). Sequence of LEEM images showing the nucleation and growth of ML-high 2D islands. Ge coverage in ML; scale bar = 2 mm. Dark areas: bottom layer, bright areas: top layer; restricted resolution of 10nm. Evolution of (top) Si 2p and (bottom) Ge 3d core level spectra during Ge deposition on a Si(111) surface at 270 ºC. The spectra were recorded using a photon energy of 130 eV. O.Mountanabbir, F.Ratto, S.Heun, K.Scheerschmidt, A.Locatelli,F.Rosei, PR B85 (2012)20141 (R)

  3. Classical molecular dynamics time-integration (fs-steps) up to relaxation (< 1ns) simultaneously 3N Newtonian equations of motion with V= empirical interaction potential <v>=.0048 A/fs sv=.0017A/fs <a>=.178 rad sa=.126 rad Relaxation during Ge-deposition onto a SiGe/(100)-Si surface: DtMD= 0.5fs Dtdepo= 17.5fs Dtframe = 0.1ps Tbulk = 400K Tdepo = 600K NpT-ensemble

  4. BOP embedded bonds instead atoms – two-center orthogonal TB density matrix instead diagonalisation – Lanczos recursion 4+ j E tot = Erep + Eprom + Eband (k)  i j j k empirical s2p2->sp3SHia,jbQia,jb  j i k i i hopping integrals BOmatrix Pettifor-Aoki Slater-Koster sss, sps, ppp... electronic hopping in closed loops j angles distance l k i dihedral ,,,, torsion + + ...... + =

  5. l k l j k i i j increased stiffness Comparison of-and-contributions -120 120 180 l k j 0 60 i -60 Si (110) surface dimerization 0K->600K->0K

  6. MD deposition - parameter overview models: 100- or 111-Si surfaces, surfaces with GeSi-islands or free standing pyramidal QDs 3x3x3ext SC = 896…928 atoms = 2.8x2.3x4.0 nm3 6x6x3ext SC = 3584…3712 atoms = 7.98x4.61x4.82 nm3 41x41x41 SC = 226751 atoms = 23.1x23.1x23.1nm3 12x21x15ext SC = ca. 358000 atoms =19.95x19.21x30.0 nm3 17x19x21ext = ca.656000 atoms = 31.9x18.4x50.0 nm3 random Ge atom depositions s= .1 …. 50% <v> = 0.0002 …. 0.05 A/fs <=> Tdepo = 100 K …. 20000 K width of incidence <a> = 0.01 …. 1.5 rad Tbulk = 200K, 300K, 400K, 500K, 600K thermostat: Berendsen, smooth, isokinetic for no, central, connected or all atoms bounds: NpT, NVE, periodicBC with free or fixed lower double layer

  7. Ge-deposition onto 111-Si with SiGe-islands (Ge red): MD-relaxed start configuration Examples of distributions for additionally deposited Ge-atoms: (i) Tdepo=900K, Tbulk=500K, 300 inclination (ii) Tdepo=3000K, Tbulk=400K, deposition on top of island

  8. potential energy, total energy and corresponding temperature of bulk and external atoms as function of deposition time (MDsteps) T ~ Ekin=Epot-Etot true deposition temperature Tdepo=Tbulk+ (Text-Tbulk)*nbulk/ndepo

  9. Ge-deposition onto 111-Si with GeSi-island (i) Tdepo=900K, Tbulk=500K, (ii) Tdepo=3000K,Tbulk=400K, 300 inclination deposition on top of the island <v>=.0014 A/fs sv=.0008 A/fs <v>=.0077 A/fs sv=.0004 A/fs <a>=.275 rad sa=.140 rad <a>=.289 rad sa=.142 rad Ge black, Si yellow and size reduced

  10. (i) layer growth between the islands snapshots at t=30ps (frame 60000) (ii) island growth mixing and exchange

  11. Details of the growth of a Ge island (case (ii), additionally deposited Ge-atoms in blue): defects and mixing within the island atomic exchange down to the second layer below the island displaced Si = 146 L0= 12 Tbulk = 400 natom = 3584 displaced Ge = 53 L1= 5 Tdepo = 3000 nadd = 270

  12. displaced Si displacedGe <v> [A/fs] Tbulk[K] <v> [A/fs] Tbulk[K] on top depositions in bulk depositions first layer deposition Preliminary Results

  13. Conclusion / Outlook Empirical molecular dynamics: nanoscopic lengths & times physical properties: TDS, phonons, … rescaled analytic TB-BOP & elastic BCs Deposition experiments: diffusion, mixing, exchange layer and island growth

  14. j j i k i Bond Order Potential • Slater-Koster products = electronic hoppings in closed loops Inter-Site On-Site separation angular functions

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