Phase diagram of III-Nitride ternary alloys

III-Nitride alloys such as InN, GaN, and AlN dominate the optoelectronics industry with applications in light emitting devices (LED), laser diodes (LD), and power electronics and constitute one of the most important semiconducting materials nowadays. In this project the bulk thermodynamics of these alloys are investigated.

Methodology:

• Density functional theory (DFT) total energy and force calculations are employed to conduct an exhaustive ground-state search and set up a Cluster-Expansion (CE) Hamiltonian.
• Canonical as well as grand canonical Monte Carlo simulations have been employed to derive the phase diagram of bulk InGaN alloys biaxially strained to GaN.

In contrast to the wide-held belief that these alloys can be described by a simple regular solution model with a large miscibility gap, this phase diagram exhibits a rich set of hitherto unknown chemically ordered phases at various stoichiometries. The mechanism that dominates the formation of these ordered phases is efficient strain accommodation on the atomic scale [1]. Furthermore, for the technologically important composition of x=25-35% ordered domains which have a √3×√3 in the basal plane pattern are found to be stable at temperatures below 700 K.