Replacing As by N in GaNAs leads to a strong perturbation of the conduction band structure, generally described using the band-anticrossing (BAC) model. We have solved the single particle Hamiltonian for a very large supercell containing randomly placed nitrogen and have calculated 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. The substitution of nitrogen atoms for a small fraction x of the group V elements in conventional III-V semiconductors such as GaAs or GaInAs strongly affects their electronic structure, with potential benefit for a range of optoelectronic devices. The rapid reduction in energy gap in GaN x As 1Àx with increasing x is well explained in terms of a bandanticrossing (BAC) interaction between the GaAs host matrix conduction band (CB) edge and a set of N resonant defect levels above the CB edge [2]. The BAC model predicts an energy gap in the CB dispersion of GaNAs, above the N resonant state energy, which makes it difficult to investigate carrier transport in dilute nitride alloys such as GaNAs. However, the density of states (DOS), measured [3] and calculated using a Green's function method [4,5], indicates a filling of this gap.We investigate here 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 GaNAs. We calculate the exact eigenstates of this Hamiltonian, and compare their behaviour with that predicted by the BAC model. Our results confirm the validity of the BAC model to describe states whose energy is
We theoretically investigate a system of two mutually delay-coupled semiconductor lasers, in a face to face configuration for integration in a photonic integrated circuit. This system is described by single-mode rate equations, which are a system of delay differential equations with one fixed delay. Several bifurcation scenarios involving multistabilities are presented, followed by a comprehensive frequency analysis of the symmetric and symmetry-broken, one-color and two-color states.
We have calculated the optical absorption for InGaNAs and GaNSb using the band anticrossing (BAC) model and a self-consistent Green’s function (SCGF) method. In the BAC model, we include the interaction of isolated and pair N levels with the host matrix conduction and valence bands. In the SCGF approach, we include a full distribution of N states, with non-parabolic conduction and light-hole bands, and parabolic heavy-hole and spin-split-off bands. The comparison with experiments shows that the first model accounts for many features of the absorption spectrum in InGaNAs; including the full distribution of N states improves this agreement. Our calculated absorption spectra for GaNSb alloys predict the band edges correctly but show more features than are seen experimentally. This suggests the presence of more disorder in GaNSb alloys in comparison with InGaNAs.
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