Another origin of bimodal size distribution in InAs self-assembled quantum dots

TL;DR

This paper investigates the growth mechanisms of InAs quantum dots on InP substrates, revealing two distinct pathways to bimodal size distribution during growth and how it transitions to unimodal distribution with increased material deposition.

Contribution

It uncovers two separate growth pathways leading to bimodal size distribution in InAs quantum dots and correlates morphological and optical data to support this growth model.

Findings

Bimodal size distribution occurs at intermediate growth stages.

Two growth pathways: abrupt nucleation and gradual evolution.

Distribution becomes unimodal with increased coverage.

Abstract

The evolution of InAs quantum dots grown on InP substrates by metal-organic vapour phase epitaxy is studied as a function of InAs coverage. Under specific growth conditions, the onset of the two- to three-dimensional transition is seen to proceed via two distinct pathways: through (i) an abrupt appearance of quantum dots as expected in the usual Stranski-Krastanov growth picture and (ii) a continuous evolution of small surface features into well developed quantum dots. The average size of the features in both these families increases with coverage, leading to a bimodal distribution in dot sizes at an intermediate stage of growth evolution that eventually becomes a unimodal distribution as more material is deposited. Complementary information obtained from independent measurements of photoluminescence spectra and surface morphology is correlated and is found to be consistent with the picture of growth proposed.