InN and GaN/InN monolayers grown on ZnO {0001}

TL;DR

This study investigates how growth rate and substrate polarity affect the growth mode and surface morphology of InN and GaN/InN monolayers grown on ZnO substrates using plasma-assisted molecular beam epitaxy, revealing critical thickness variations.

Contribution

It provides new insights into the influence of growth parameters and substrate polarity on InN and GaN/InN monolayer growth behavior and critical thickness for relaxation.

Findings

Transition from 2D to 3D growth mode during InN deposition.

Critical thickness for relaxation varies with growth rate and substrate polarity.

GaN on InN shows near-zero relaxation thickness on O-ZnO.

Abstract

Thin InN and GaN/InN films were grown on oxygen-polar (O) (000-1) and zinc-polar (Zn) (0001) zinc oxide (ZnO) by plasma-assisted molecular beam epitaxy (PAMBE). The influence of the growth rate (GR) and the substrate polarity on the growth mode and the surface morphology of InN and GaN/InN was investigated in situ by reflection high-energy electron diffraction (RHEED) and ex situ by atomic force microscopy (AFM). During InN deposition, a transition from two dimensional to three dimensional (2D-3D) growth mode is observed in RHEED. The critical thickness for relaxation increases with decreasing GR and varies from 0.6 ML (GR: 1.0 ML/s) to 1.2 MLs (GR: 0.2 ML/s) on O-ZnO and from 1.2 MLs (GR: 0.5 ML/s) to 1.7 MLs (GR: 0.2 ML/s) on Zn-ZnO. The critical thickness for relaxation of GaN on top of 1.2 MLs and 1.5 MLs thick InN is close to zero on O-ZnO and 1.6 MLs on Zn-ZnO, respectively.