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

TL;DR

This study investigates how the geometry of selective-area patterns influences the alloy composition of InGaAs inserts in GaAs nanopillars grown by MOCVD, revealing pattern-dependent variations in In incorporation.

Contribution

It demonstrates the dependence of InGaAs alloy composition on pattern geometry and provides a model based on adatom capture coefficients to explain this behavior.

Findings

InGaAs composition varies with pattern pitch and diameter.

Decreasing pitch increases In enrichment in the alloy.

Gallium incorporation is more affected by pattern geometry.

Abstract

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.