Nucleation and Growth of GaN/AlN Quantum Dots

TL;DR

This paper investigates the nucleation and growth stages of GaN quantum dots on AlN substrates, revealing a four-stage growth process and analyzing how temperature and coverage affect island morphology.

Contribution

It provides a detailed analysis of the nucleation, growth stages, and the effects of temperature and coverage on GaN quantum dot formation using an equilibrium model.

Findings

Identification of four distinct growth stages.

Observation of saturation in island density.

Bimodal height distribution at advanced growth stages.

Abstract

We study the nucleation of GaN islands grown by plasma-assisted molecular-beam epitaxy on AlN(0001) in a Stranski-Krastanov mode. In particular, we assess the variation of their height and density as a function of GaN coverage. We show that the GaN growth passes four stages: initially, the growth is layer-by-layer; subsequently, two-dimensional precursor islands form, which transform into genuine three-dimensional islands. During the latter stage, island height and density increase with GaN coverage until the density saturates. During further GaN growth, the density remains constant and a bimodal height distribution appears. The variation of island height and density as a function of substrate temperature is discussed in the framework of an equilibrium model for Stranski-Krastanov growth.