Self-formed compositional superlattices triggered by cation orderings in m-plane Al(1−x)In(x)N on GaN

Immiscible semiconductors are of premier importance since the source of lighting has been replaced by white light-emitting-diodes (LEDs) composed of thermodynamically immiscible In(x)Ga(1−x)N blue LEDs and yellow phosphors. For realizing versatile deep-ultraviolet to near-infrared light-emitters, Al(1−x)In(x)N alloys are one of the desirable candidates. Here we exemplify the appearance and self-formation sequence of compositional superlattices in compressively strained m-plane Al(1−x)In(x)N films. On each terrace of atomically-flat m-plane GaN, In- and Al-species diffuse toward a monolayer (ML) step edge, and the first and second uppermost < [Formula: see text] > cation-rows are preferentially occupied by Al and In atoms, respectively, because the configuration of one In-N and two Al-N bonds is more stable than that of one Al-N and two In-N bonds. Subsequent coverage by next < [Formula: see text] > Al-row buries the < [Formula: see text] > In-row, producing nearly Al(0.5)In(0.5)N cation-stripe ordering along [0001]-axis on GaN. At the second Al(0.72)In(0.28)N layer, this ordinality suddenly lessens but In-rich and In-poor < [Formula: see text] >-rows are alternately formed, which grow into respective {0001}-planes. Simultaneously, approximately 5-nm-period Al(0.70)In(0.30)N/Al(0.74)In(0.26)N ordering is formed to mitigate the lattice mismatch along [0001], which grow into approximately 5-nm-period Al(0.70)In(0.30)N/Al(0.74)In(0.26)N {[Formula: see text] } superlattices as step-flow growth progresses. Spatially resolved cathodoluminescence spectra identify the emissions from particular structures.