First-principles calculation of the thermodynamics of In$_x$Ga$_{1-x}$N alloys: Effect of lattice vibrations

TL;DR

This study uses first-principles calculations to analyze the thermodynamics of InGaN alloys, highlighting the significant impact of lattice vibrations on phase stability and phase diagrams, aligning well with experimental data.

Contribution

It introduces the inclusion of lattice vibrations in first-principles thermodynamic calculations of InGaN alloys, improving phase diagram accuracy.

Findings

Lattice vibrations significantly reduce critical temperatures.

Inclusion of vibrations alters solubility and spinodal curves.

Predicted phase diagrams agree with experimental measurements.

Abstract

The thermodynamics properties of the wurtzite and zinc-blende \InGaN alloys are calculated using first-principles density-functional calculations. Special quasi-random structures are used to describe the disordered alloys, for $x= 1/4, 1/2$, and 3/4. The effect of lattice vibrations on the phase diagram, commonly omitted from semiconductor alloy phase diagram calculations, are included through first-principles calculations of phonon spectra. Inclusion of lattice vibrations leads to a large reduction in the order-disorder critical temperature ($\sim 29$% and $\sim 26$% for the wurtzite and zinc-blende structures, respectively) and changes the shape of the solubility and spinodal curve through changes in the entropies of the competing phases. Neglect of such effect produces significant errors in the phase diagrams of complex ordered semiconductor compounds. The critical temperature for phase separation is 1654 K (1771 K) for the wurtzite (zinc-blende) structures. The predicted phase diagrams are in agreement with experimental measurements on MOCVD \InGaN\ films.