Dependence of the electronic structure of $\beta$-Si$_{6-z}$Al$_{z}$O$_{z}$N$_{8-z}$ on the (Al,O) concentration $z$ and on the temperature

TL;DR

This study investigates how the electronic structure of SiAlON materials varies with (Al,O) concentration and temperature using ab initio calculations, revealing a decreasing band gap and temperature-induced band shifts.

Contribution

It provides a detailed ab initio analysis of the effects of composition and temperature on SiAlON electronic properties, including semiordered and disordered structures.

Findings

Band gap decreases by about 1.5 eV from z=0 to z=2.

Valence band states are mainly from N atoms.

Conduction band bottom shifts to lower energies with increasing temperature.

Abstract

SiAlON is a prominent example of systems suitable as hosts for creating materials for light-emitting diodes (LEDs). In this work, the electronic structure of a series of semiordered and disordered SiAlON systems is investigated by means of ab initio calculations, using the FLAPW and Green function KKR methods. Finite temperature effects are included by averaging over thermodynamic configurations within the alloy analogy model. We found that the dependence of the electronic structure on the (Al,O) concentration $z$ is similar for semiordered and disordered structures. The electronic band gap decreases with increasing $z$ by about 1.5 eV when going from $z$=0 to $z$=2. States at the top of the valence band are mostly associated with N atoms whereas the states at the bottom of the conduction band are mostly derived from O~atoms. Increasing the temperature leads to a shift of the bottom of the conduction band to lower energies. The amount of this shift increases with increasing $z$.