Empirical tight-binding sp3s* band structure of GaAs, GaP, AlAs, InAs, C (diamond) and Si

The input files to be used are:

  • 1D_TightBinding_bulk_GaAs.in

  • 1D_TightBinding_bulk_GaAs_so.in

  • 1D_TightBinding_bulk_Al0.3Ga0.7As.in

  • 1D_TightBinding_bulk_GaP.in

  • 1D_TightBinding_bulk_GaP_so.in

  • 1D_TightBinding_bulk_AlAs.in

  • 1D_TightBinding_bulk_AlAs_so.in

  • 1D_TightBinding_bulk_C.in

  • 1D_TightBinding_bulk_Si.in

  • 1D_TightBinding_bulk_Ge.in

  • 1D_TightBinding_bulk_InAs_so.in

  • 1D_TightBinding_bulk_AlSb_so.in

  • 1D_TightBinding_bulk_InSb_so.in

  • 1D_TightBinding_bulk_Al0.5In0.5Sb.in

Empirical tight-binding sp3s* band structure of GaAs and GaP

The empirical tight-binding model that is used here is based on the sp3s* Hamiltonian, i.e. the 10 x 10 matrix given in Table (A) of [VoglJPCS1983].

In addition, we include spin-orbit coupling leading to a 20 x 20 matrix. The additional terms arising due to spin-orbit coupling are given for instance on p. R5 of [CarloSST2003].

We note that nowadays much better theoretical methods are available for calculating the band structure of bulk materials. However, for educational purposes, the chosen sp3s* method should be sufficient.

In this tutorial, we calculate the bulk band structure of

  • GaAs, GaP and AlAs without spin-orbit coupling using the parameters of [VoglJPCS1983] at T = 0 K

  • GaAs, GaP and AlAs including spin-orbit coupling using the parameters of [KlimeckSM2000] at T = 300 K

Input

The values for the tight binding parametrization have to be specified in the input file:

$numeric-control
...
!------------------------------------------------------------------------------
! Tight-binding parameters for GaAs (values of [Klimeck]). The units are [eV].
!------------------------------------------------------------------------------
!tight-binding-parameters = -3.53284d0             ! Esa (GaAs)
                             0.27772d0             ! Epa
                            -8.11499d0             ! Esc
                             4.57341d0             ! Epc
                            12.33930d0             ! Es_a
                             4.31241d0             ! Es_c
                            -6.87653d0             ! Vss
                             1.33572d0             ! Vxx
                             5.07596d0             ! Vxy
                             0d0                   ! Vs_s_
                             2.85929d0             ! Vsa_pc
                            11.09774d0             ! Vsc_pa
                             6.31619d0             ! Vs_a_pc
                             5.02335d0             ! Vs_c_pa
                             0.32703d0  0.12000d0  ! Delta_so_a Delta_so_c
! Note: a = anion, c = cation
!       s_ = s*

For more information about the meaning of these parameters, refer to the above cited references.

Output

The output of the calculated tight-binding band structure can be found in the following file: TightBinding/BandStructure.dat

The first column contains the number of the grid point in the Brillouin zone. These grid points run

  • from L point to Gamma point (along Lambda)

  • from Gamma point to X point (along Delta)

  • from X point to the U, K points

  • from U,K points to Gamma point (along Sigma)

The next columns are the eigenvalues of the tight-binding Hamiltonian in units of [eV] for each grid point in k = (kx, ky, kz) space.

The file TightBinding/BandStructure_without_so.dat contains the tight-binding band structure without spin-orbit coupling.

The file TightBinding/k_vectors.dat contains for each point the information to which k point it belongs to.

no.

kx

ky

kz

|k|

kx [2pi/a]

ky [2pi/a]

kz [2pi/a]

|k| [2pi/a]

1

0.314159E+01

0.314159E+01

0.314159E+01

0.544140E+01

0.500000E+00

0.500000E+00

0.500000E+00

0.866025E+00

Note: Currently the units of kx, ky and kz do not take into account the lattice constant a. This should be modified. The values for kx, ky and kz in units of [2pi/a] are correct, however. Another improvement would be to calculate and output the three-dimensional energy dispersion E(kx, kz, kz) and two-dimensional slices E(kx, kz, 0) through the three-dimensional energy dispersion E(kx, kz, kz) for a constant value of kz, e.g. kz =0.

Results

GaAs without spin-orbit coupling from 1D_TightBinding_bulk_GaAs.in

../../../_images/BandStructureGaAs_Vogl.jpg

The calculated band structure is in excellent agreement with Fig. 11(d) of [VoglJPCS1983]. The conduction band minimum is at the Gamma point (direct band gap). Because spin-orbit coupling is not included in the Hamiltonian, the sp3s* empirical tight-binding parameters were taken from [VoglJPCS1983] at T = 0 K.

GaAs including spin-orbit coupling from 1D_TightBinding_bulk_GaAs_so.in

../../../_images/BandStructureGaAs_so_Klimeck.jpg

The calculated band structure is in excellent agreement with Fig. 1 of [KlimeckSM2000]. The conduction band minimum is at the Gamma point (irect band gap). Spin-orbit coupling lifts the degeneracy of heavy/light hole and split-off hole at the Gamma point. Heavy and light hole are still degerate at the Gamma point. The sp3s* empirical tight-binding parameters were taken from [KlimeckSM2000] at T = 300 K.

GaP without spin-orbit coupling from 1D_TightBinding_bulk_GaP.in

../../../_images/BandStructureGaP_Vogl.jpg

The calculated band structure is in excellent agreement with Fig. 2 of [VoglJPCS1983]. The conduction band minimum is calculated to be at the X point (indirect band gap). Because spin-orbit coupling is not included in the Hamiltonian, heavy, light and the split-off hole are degenerate at the Gamma point, i.e at k = (kx, ky, kz) = 0. The sp3s* empirical tight-binding parameters were taken from [VoglJPCS1983] at T = 0 K.

GaP including spin-orbit coupling from 1D_TightBinding_bulk_GaP_so.in

../../../_images/BandStructureGaP_so_Klimeck.jpg

The calculated band structure is in excellent agreement with Fig. 1 of [KlimeckSM2000]. The conduction band minimum is in the vincinity of the X point at the Delta line (indirect band gap), so-called camel’s back. Spin-orbit coupling lifts the degeneracy of heavy/light hole and split-off hole at the Gamma point. Heavy and light hole are still degenerate at the Gamma point. The sp3s* empirical tight-binding parameters were taken from [KlimeckSM2000] at T = 300 K.

AlAs without spin-orbit coupling from 1D_TightBinding_bulk_AlAs.in

../../../_images/BandStructureAlAs_Vogl.jpg

InAs including spin-orbit coupling from 1D_TightBinding_bulk_InAs_so.in

../../../_images/BandStructureInAs_so_Klimeck.jpg

C (diamond) without spin-orbit coupling from 1D_TightBinding_bulk_C.in

../../../_images/BandStructureC_Vogl.jpg

Si (silicon) without spin-orbit coupling from 1D_TightBinding_bulk_Si.in

../../../_images/BandStructureSi_Vogl.jpg

The k space resolution, i.e. the number of grid points on the axis of these plots can be adjusted. This can be done with:

$tighten
calculate-tight-binding-tighten = no
destination-directory           = TightBinding/
number-of-k-points              = 50             ! This number corresponds to 50 k points between the Gamma point and the X point
                                                 ! The number of k points along the other directions are scaled accordingly.