The III-V semiconductors with nitrogen as the fifth-group element have unique properties that make them very attractive for short-wavelength light emitters and high-power/high-temperature electronics applications. In order to provide the adequate performance of electronic devices, these materials must have reliable electronic properties. It is well known, however, that the electronic properties of multicomponent semiconductors are very sensitive to the uniformity of their chemical composition. The inhomogeneities can affect device performance via changes of the band gap energy and localized variations of polarization field.

There exists experimental evidence that III-V alloys are often
unstable against phase separation, spatial fluctuations in the second component concentration, or partial ordering. Compositional inhomogeneity (clustering or phase separation) has been experimentally observed, in particular, in InGaN. The microscopic reasons for ordering in InGaN and the ordered structure patterns have been already extensively studied in the literature. Unfortunately, the majority of the theoretical investigations are based on analytical models, which makes the reliability of such predictions uncertain.

In this work we study the minor component ordering in wurtzite Ga_1-xIn_xN and Ga_1-xAl_xN alloys by the multiscale approach that combines the accurate total-energy density functional calculations and lattice kinetic Monte-Carlo simulation. According to our results In in GaN forms [0001] aligned pairs or chains and, at higher In concentrations, zigzag chains in c-direction, while Al forms a random alloy with the matrix material. The increase of In concentration above 25-30% is shown to lead to the phase separation and formation of InN regions. The effect of the minor component (In,Al) ordering pattern on the band gap of the ternary Ga(In,Al)N alloy is also discussed.

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