Chemically ordered Al(x)Ga(1-x)N alloys: Spontaneous formation of natural quantum wells

We combine transmission electron microscopy, high-resolution x-ray diffraction, cathodoluminescence, and photoluminescence experiments with first-principles calculations to study the formation, thermodynamic stability, structural, and optical properties of chemically ordered Al(x)Ga(1-x)N alloys (0<x<1). Our results reveal that group-III-nitride surfaces exhibit chemically highly sensitive adsorption sites at step edges and that these sites can be used to kinetically engineer chemically ordered Al(x)Ga(1-x)N alloys. The ordered alloys have unique properties: (i) the band gap is redshifted up to 110 meV with respect to the disordered alloy of the same composition and (ii) the band gap reduction is caused by localization of the band edge wave functions in the GaN layer. Ordered Al(x)Ga(1-x)N thus can be seen as a natural quantum well structure where electrons and holes are localized and confined in monolayer GaN quantum wells.