Centre d’Élaboration de Matériaux et d’Etudes Structurales (UPR 8011)


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Wires or islands in the Stranski-Krastanov growth mode ? It is a matter of surface energy.

par Evelyne Prevots - publié le

The frequent formation of InAs wires during the Stranski-Krastanov growth of InAs on InP substrates was attributed to the surface diffusion anisotropy of indium atoms. We propose a model integrating the anisotropy of the InAs surface energy. Without resorting to any kinetic mechanism, our model predicts a wire-to-island shape transition in agreement with the experimental observations.

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Forme d’équilibre (longueur LES, largeur wES et hauteur hES) en fonction du volume de la nanostructure InAs en croissance sur substrat InP, déterminée pour les densités d’énergies de surface d’InAs indiquées. Les images expérimentales AFM font 300 nm x 300 nm.

To account for wire formation and wire-to-island shape transition observed during the growth of InAs on (001)InP substrates, an experimental study was combined with an analysis based on an equilibrium shape model.

Due to the 3.2% misfit, the growth mode by molecular beam epitaxy (MBE) is Stranski-Krastanov (SK) (formation of InAs nanostructures). Formation of elongated wires rather than islands is frequently observed in the first steps of the SK growth mode. It was attributed to a kinetic mechanism, the anisotropy of surface diffusion of Indium atoms.

Our hypothesis is that the equilibrium shape itself varies with the volume of the InAs nanostructure, due to the anisotropy of surface energy of the lateral facets of the III-V nanostructures (A or B facets parallel to [-110] and [110] respectively). This surface energy anisotropy is considered to determine the nanostructure equilibrium shape from the balance between the elastic energy and the surface energy (calculated respectively by finite element method and by density functional theory DFT). At low volumes, the most energetically favorable shape is the wire-like shape, while at high volumes, the equilibrium shape is the island-like shape. The calculated sizes for which the shape changes are in good agreement with experimental sizes from our experiments. The low lattice mismatch and the low surface energy of (114)A InAs facets around 41 meV/A2, as obtained from our DFT calculations, enhance this effect in the InAs/InP system.

Collaboration with FOTON, INSA Rennes.

 

 

Reference

Shape transition in InAs nanostructures formed by Stranski-Krastanow growth mode on InP (001) substrate
A. Ponchet, L. Pedesseau, A. Le Corre, C. Cornet and N. Bertru.
Appl. Phys. Lett. 114, 173102 (2019)
https://doi.org/10.1063/1.5091058

 

Contacts

 

Anne Ponchet, CEMES-CNRS

Nicolas Bertru, FOTON-INSA