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The Dependence of Alloy Composition of InGaAs Inserts in GaAs Nanopillars on Selective-Area Pattern Geometry

GaAs nanopillars with 150 nm - 200 nm long axial InGaAs inserts are grown by MOCVD via catalyst-free selective-area-epitaxy (SAE). The alloy composition of the InGaAs region, as determined by room-temperature photoluminescence (PL), depends critically on the pitch and diameter of the selective-area pattern geometry. The PL emission varies based on pattern geometry from 1.0 \{mu}m to 1.25 \{mu}m corresponding to a In to Ga ratio from 0.15 to > 0.3. This In enrichment is explained by a pattern dependent change in the incorporation rate for In and Ga. Capture coefficients for Ga and In adatoms are calculated for each pattern pitch. As the pitch decreases, these data reveal a contest between a synergetic effect (related to nanopillar density) that increases the growth rate and a competition for available material that limits the growth rate. Gallium is more susceptible to both of these effects, causing the observed changes in alloy composition.