Analysis of the BAC model in GaNAs near localised states

Fig. 1: The Density of states projected onto selected GaAs k states
Fig. 1: The Density of states projected onto selected GaAs k states

Materials Theory Group > Transport and Atomic Structure in Semiconductor Alloys > Dilute Nitrides > Analysis of the BAC model in GaNAs near localised states

We investigate, the accuracy of the BAC model in describing the band structure of GaNAs, including the electronic structure both away from and close to the N resonant state energy. We directly solve a simplified random impurity model Hamiltonian for a very large supercell of GaNxAs1-x. We calculate the exact eigenstates of this Hamiltonian, and compare their behaviour with that predicted by the BAC model. We solve the single particle Hamiltonian for a very large supercell containing randomly placed nitrogen and calculate the fractional G character, localisation factor and the density of states in the supercell. Comparison of these results with those calculated by the 2-level BAC model confirms the validity of the BAC model at energies away from N state energies but highlights the role of disorder at energies close to the N state energy. We create a supercell of size L3 containing M nitrogen sites at random and solve the supercell-zone centre Hamiltonian (L = 100 a0, M = 8000, x = 0.2%).

We have shown by direct comparison with a supercell model Hamiltonian that the BAC model provides a good description of the electronic structure of dilute nitride alloys at energies which are well separated from the N state energy. For simplicity, we have neglected the effect of nitrogen pairs or larger clusters, that would provide further perturbation and localisation in conduction band of the host semiconductor [2]. Our calculations show that the electronic structure deviates from that predicted using the BAC model close to the N resonant state energy, due to the finite density of N-related states, and carrier localisation effects (breakdown of k selection). We conclude that it may be necessary when modeling transport to consider hopping through the N states, at energies close to the N resonant state and BAC energy gap range.

Figure 1 shows The Density of states projected onto selected GaAs k states, calculated using the BAC model (dashed red lines) and using the numerical model for a box with L_0=100, l=11, M=1000 (solid blue lines), and the BAC model (dashed red lines). Arrows show the energy EM of the original k state, and dotted line displays the N energy, EN.

Figure 2 shows (a) The DOS projected onto the GaAs CB states for GaAs1-xNx with x = 0.2%; obtained from: (i) the BAC model with and without N broadening, and assuming Emax = ∞ (dashed red and dashed-dotted grey lines, respectively), (ii) a supercell calculation including 8000 N (solid blue line), and (iii) a Green’s function method with Emax = 0.857 eV (green dots). (b) Comparison between the total DOS (blue solid line), and the DOS projected onto the host CB states (red dashed line). The inset shows the GaAs DOS calculated for a supercell (solid line) and analytically (dashed line).

 

Related people

    Masoud Seifikar
    Stephen Fahy
    Eoin O'Reilly

 

Related publications

Analysis of band-anticrossing model in GaNAs near localised states
M. Seifikar, E.P. O’Reilly and S. Fahy,
Physica Status Solidi B, 248: n/a. doi: 10.1002/pssb.201000784 (2011)

 

Related presentations

M. Seifikar, E.P. O'Reilly and S. Fahy, Theory of Scattering and Impact Ionization in Dilute Nitride Avalanche Photodiodes,
EMRS, Strasbourg 2010

M. Seifikar, E.P. O'Reilly and S. Fahy, Analysis of Band-Anticrossing Model in GaAs1-xNx Dilute Nitride Alloys,
14th Irish Nanoscale Simulators Meeting, 2011

M. Seifikar, E.P. O'Reilly and S. Fahy, Theory of Scattering and Impact Ionization in Dilute Nitride Avalanche Photodiodes,
Inspire video conference seminars, 2010

M. Seifikar, E.P. O'Reilly and S. Fahy, High Field Transport in GaAs1-xNx Dilite Nitride Alloys (poster),
Fabrication to Application Workshop, Tyndall National Institute, 2010

M. Seifikar, E.P. O'Reilly and S. Fahy, Theory of Scattering and Impact Ionization in Dilute Nitride Avalanche Photodiodes (poster),
Joint CECAM Nano-Structures Workshop, Tyndall National Institute, Ireland / University of Manchester, UK

M. Seifikar, E.P. O'Reilly and S. Fahy, High Field Transport in GaAs1-xNx Dilite Nitride Alloys (poster),
Photonics Ireland 2009, Kinsale, Ireland, 2009

M. Seifikar, E.P. O'Reilly and S. Fahy, Theory of Scattering and Impact Ionization in Dilute Nitride Avalanche Photodiodes (poster),
5th International Summer School New Frontiers in Optical Technologies, Tampere, Finland, 2009

 

Related pages

    High Field Mobility in Dilute Nitride Alloys
    The Density of States in GaAs:N
    Mobility in GaAs:N
    Dilute Nitride Materials 

 

References

[1] W. Shan, W. Walukiewicz, J.W. Ager, E.E. Haller, J. F. Geisz, D. J. Friedman, J.M. Olson, and S.R. Kurtz, Phys. Rev. Lett. 82, 1221 (1999)
[2] A. Lindsay and E. P. O’Reilly, Phys. Rev. Lett. 93, 196402 (2004)

Ireland fund ecsf ucc
Privacy - Legal Statements
Tyndall - All rights reserved - 2014