Ab initio Calculation of Structural and Electronic Properties of Interfaces between Ionic Compounds:

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Ab initio Calculation of Structural and
Electronic Properties of Interfaces between Ionic
Compounds PbTe(rs)/CdTe(zb)
Roman Leitsmann, L. E. Ramos, and F. Bechstedt
Institut für Festkörpertheorie- und optik
Friedrich-Schiller-Universität Jena
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Motivation

• Experiment

• Quantum-Dots are formed by an annealing process
  
• W. Heiss, F. Schäffler et al. arXivcond-mat
  0602516(2006)
• they exhibit (110), (100), and (111) facets
• they show intense mid-infrared luminescence
• high potential for future applications like
• mid-infrared quantumdot-laser
• devices in medical diagnostics
• mid-infrared spectroscopy

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Motivation

• Theory

• computational demanding
• shallow Cd d-states
• relativistic effects
• exhibit a different lattice structure (PbTe-rs
  CdTe-zb)
• hence we find a new kind of interfaces
• PbTe and CdTe are nearly ionic crystals
• artificial electric fields are induced in the
  slab-approx.

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Numerical Details

• Dipole correction

We compensate the artificial dipole potential ?
with a ramp-shaped potential
Calculate interface energies by total energy
differences
Energy corrections due to artificial dipole
potential ?
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Numerical Details

• DFT-LDA ground state calculations (VASP 4.6.20)
• projector augmented wave (PAW) pseudopotentials
• 200 eV plane wave-cutoff
• preconditioned residuum-minimization method for
  the
• electronic relaxation
• conjugate-gradient-algorithm for the ionic
  relaxation

• DFT-LDA ground state calculations (VASP 4.6.20)
• projector augmented wave (PAW) pseudopotentials
• 200 eV plane wave-cutoff
• preconditioned residuum-minimization method for
  the
• electronic relaxation
• conjugate-gradient-algorithm for the ionic
  relaxation

• DFT-LDA ground state calculations (VASP 4.6.20)
• projector augmented wave (PAW) pseudopotentials
• 200 eV plane wave-cutoff
• preconditioned residuum-minimization method for
  the
• electronic relaxation
• conjugate-gradient-algorithm for the ionic
  relaxation

• DFT-LDA ground state calculations (VASP 4.6.20)
• projector augmented wave (PAW) pseudopotentials
• 200 eV plane wave-cutoff
• preconditioned residuum-minimization method for
  the
• electronic relaxation
• conjugate-gradient-algorithm for the ionic
  relaxation

• DFT-LDA ground state calculations (VASP 4.6.20)
• projector augmented wave (PAW) pseudopotentials
• 200 eV plane wave-cutoff
• preconditioned residuum-minimization method for
  the
• electronic relaxation
• conjugate-gradient-algorithm for the ionic
  relaxation

• Interface calculations
• (2x1)slabs with 28 or 24 double layers
• use a set of Monkhorst-Pack k-points (7x5),
  (7x7), (5x9)

• Interface calculations
• (2x1)slabs with 28 or 24 double layers
• use a set of Monkhorst-Pack k-points (7x5),
  (7x7), (5x9)

• Interface calculations
• (2x1)slabs with 28 or 24 double layers
• use a set of Monkhorst-Pack k-points (7x5),
  (7x7), (5x9)

100
111
110
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Results

• PbTe/CdTe (110)

• excellent agreement with experiment Leitsmann
  et al. PRL(submitted)

• lateral offset of 0.038 nm
• rumpling effect
• interface energy 0.20 J/m2

green- 110 direction red - 001 direction
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Results

• PbTe/CdTe(100)

• Cd- or Te-terminated interfaces with different
  separations
• no lateral displacements

• small rumpling effect
• interface energy 0.23 J/m2
• Leitsmann et al. PRL(submitted)

Te-terminated
Cd-terminated
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Results

• Interface bandstructure

• LDA-band-gap
• L-point 0.58 eV
• indirect L-? 0.19 eV
• relativistic-band-gap
• L-point 0.15 eV
• indirect L-? 0.29 eV

• experimental band-gaps
• PbTe 0.19 eV CdTe 1.6 eV
• P. Dziawa et al. phys.stat.sol. 2,1167(2005)
• no indications for interface states at
  PbTe/CdTe(110) in the gap

PbTe/CdTe(110) interface LDA-bandstructure
PbTe/CdTe(110) interface relativistic-bandstructur
e
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Summary / Outlook
Results
R. Leitsmann et al. PRL (submitted)

• introduced a method to compensate artificial
  boundary effects at polar interfaces
• investigated structural properties of
  PbTe(rs)/CdTe(zb) interfaces excellent agreement
  with experiment
• calculated the interface bandstructure of the
  PbTe/CdTe (110) interface no interface states
  

Next goals

• electronic properties of the polar PbTe/CdTe
  (100) and (111) interfaces
• absorption spectra of quantum-wall and
  quantum-dot systems
• ab initio description of embedded PbTe-dots in
  CdTe-matrix

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Thank you for your attention.