Electronic Properties of PbTeCdTe 100 interfaces

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Electronic Properties of PbTe/CdTe (100)
interfaces
Sponsored by
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Motivation

• PbTe/CdTe

• PbTe Quantum-Dots are formed by an annealing
  process
• W. Heiss et al. Appl. Phys. Lett. 88, 192109(
  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

• Theoretical Problems using periodic boundary
  conditions
• two in general different A- and B-interfaces
• induced dipole field at polar interfaces ( -
  ... - -)
• charge transfer ? ionization degree of interface
  atoms

Energy
Position along 100
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Modelling
Slab-Approximations
Four Supercell modells for electronic
bandstructure calculations
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Modelling
Bulk-Properties
PbTe
rocksalt structure fundamental gap at L-point
0.19 eV
P. Dziawa et al. phys.stat.sol c. 2,1167(2005)
CBO 1.0 eV VBO 0.4 eV
R.Leitsmann (to be published)
CdTe
zinc blende structure fundamental gap at G-point
1.6 eV
P. Dziawa et al. phys.stat.sol. c 2,1167(2005)
6

• Stoichiometric slab approximation

• Induced dipole potential
• charge transfer
• partiall ionized interface atoms

• Metallic band structure
• occupied conduction bands
• empty valence bands

Not suitable for isolated interfaces
Suitable for layered heterostructures

• Band structure
• Energy alignment

B-interf.
A-interf.
B-interf.
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• Non-stoichiometric slab approximation

• No dipole potential
• no charge transfer
• partiall ionized interface atoms

• Metallic band structure
• shifted Fermi-level
• interface states (1/2cK, 1cJ)

• Suitable for
• isolated interfaces
• layered heterostructures

• Band structure
• Energy alignment

B-interf.
B-interf.
B-interf.
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Summary/Conclusions
Calculation of polar interface band structures
different situations different modells
Non-stoichiometric Slab Approx.
Dipole corrected Slab Approx.
Stoichiometric Slab Approx.
Vacuum Slab Approx.
symmetry constrained sys.
layered herterostructures
isolated interfaces
Cd-terminated PbTe/CdTe(100) interface band
structure
several interface states
metallic character
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Thank you for your attention.
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10
Results

• Dipole corrected slab approximation

• Comp. dipole potential
• no charge transfer
• fully ionized interface atoms

• Semicond. band structure
• filled/empty bands
• interface states (1cK, 1cJ, 1vG)

• Suitable for
• field-free interfaces
• e.g. dot-matrix interfaces

• Interface band structure
• Energy alignment

A-interf.
B-interf.
A-interf.
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Results

• Vacuum slab approximation

• Dipole potential within CdTe
• no charge transfer
• partiall ionized interface atoms

• Metallic band structure
• shifted Fermi-level
• interface states (1/2cK, 1cJ)

• Suitable for
• isolated interfaces
• BUT not as good as N-SA

• Interface band structure
• Energy alignment

A-interf.
surfaces
A-interf.
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Additional information

• Dipole correction

We compensate the artificial dipole potential ?
with a ramp-shaped potential
plane averaged potential
Calculate interface energies by total energy
differences
Energy corrections due to artificial dipole
potential ?
position along 100
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Band offset

• Alignment of electrostatic potentials

Two step procedure
PbTe
CdTe
?VBM
VBM(CdTe)
VBM(PbTe)
?(PbTe-CdTe)

• bulk calculation of VBM w.r.t. the
  plane-averaged potential
• interface calculation of ?(PbTe-CdTe) ? ?VBM

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Results

• Band offset

Type- I heterostructure
LDA
LDASO
? results are used to correctly align the
interface bandstructures
Experimental-gap PbTe 0.19 eV L-point
CdTe 1.6 eV ?-point P. Dziawa et al.
phys.stat.sol. 2,1167(2005)
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Results

• Bulk PbTe

Well-known problems with PbTe
Experimental-gap 0.19 eV (L-point) P. Dziawa
et al. phys.stat.sol. 2,1167(2005)

• too large LDA-gap 0.58 eV
• negative LDASO-gap -0.12 eV
• reasonable HSESO-gap 0.15 eV

LDA LDASO HSESO
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Results

• Bulk PbTe

Well-known problems with PbTe
Experimental-gap 0.19 eV (L-point) P. Dziawa
et al. phys.stat.sol. 2,1167(2005)

• too large LDA-gap 0.58 eV
• negative LDASO-gap -0.12 eV
• reasonable HSESO-gap 0.15 eV
• ? but HSE is not suitable for interface
  calculations !

LDA LDASO HSESO
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Results

• Bulk PbTe

Well-known problems with PbTe
Experimental-gap 0.19 eV (L-point) P. Dziawa
et al. phys.stat.sol. 2,1167(2005)

• too large LDA-gap 0.58 eV
• negative LDASO-gap -0.12 eV
• reasonable HSESO-gap 0.15 eV
• ? but HSE is not suitable for interface
  calculations !

? qualitative HSE and LDA differ only near the
L-point
LDA LDASO HSESO