Modelling of AlN/GaN superlattices for integration in near-UV distributed Bragg reflectors
Résumé
One of the main problem for the realization of high reflectivity GaN-based Bragg mirrors operating in the near-UV wavelength range is to limit the crack formation due to the lattice mismatch between the different nitride compounds while keeping a large refractive index contrast. Recent works have demonstrated that the introduction of several AlN/GaN superlattices (SLs) in a classical AlN/GaN quarter wavelength layers mirror structure strongly improved the crystalline quality and therefore the optical properties of such a mirror. In this work, several AlN/GaN SLs were studied for their direct use as pseudo-alloy layers pair material in a Bragg mirror. Such a configuration should allow combining the limitation of cracks by SLs with the improvement of the index contrast. First, the band structure of different AlN/GaN SLs was simulated using a self-consistent 8-band-k.p Schrödinger-Poisson solver. Then, the influence of surrounding layers such as AlN bulk ones on the band structure were considered. Using miniband-to-miniband transitions deduced from these calculations, refractive indices of these SLs were finally estimated for the design of an optimized high reflective Bragg mirror at 450 nm.