Servicenavigation

Detailseite

Zurück

Projekt Druckansicht

Stabilität von Fehlpassungsversetzungen in axial-heteroepitaktischen Nanostabstrukturen

Fachliche Zuordnung Experimentelle Physik der kondensierten Materie
Förderung Förderung von 2015 bis 2021
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 286465872
 
Erstellungsjahr 2019

Zusammenfassung der Projektergebnisse

Axial nanopillar heterostructures with controlled lengths of the semiconductor segments offer the possibility to create tailor-made electronic confinements and therefore have been attracting increasing interest for use in optoelectronic applications. As misfit dislocations and their concomitant electronic states can severely degrade device performance, knowledge of the critical dimensions for misfit dislocation formation is essential. In the present project these critical dimensions have been determined experimentally and theoretically for InAs growth on top of GaAs nanopillars with diameters of 20 – 45 nm and heights of 80 – 90 nm. Experimentally, the growth has been performed by molecular beam epitaxy on GaAs(111)A substrates, which had been nanopillar-patterned by means of nanosphere lithography and anisotropic reactive ion etching. The resulting InAs morphology shows a strong dependence on the growth temperature: At temperatures below 200°C InAs islands are formed on pillar tops due to the limited surface migration length, whereas for temperatures above 250°C InAs grows preferentially at the pillar bases acting as adatom sinks. The islands on the pillar tops mostly have a triangular in-plane shape and are preferentially located at off-centre positions, which has been interpreted by Tersoff potential based, atomistic molecular statics modeling of the energy, the strain distribution and the number of broken bonds of surface atoms. These simulations reveal the existence of preferred nucleation sites displaced from the nanopillar axis such that the outer island edge approximately matches the pillar edge. Aberration-corrected scanning transmission electron microscopy imaging shows that InAs islands, whose dimensions exceed ~10 nm width and ~7 nm height on 25 – 30 nm diameter pillars, contain one or more 60° dislocations directly at the heterointerface, while smaller ones are dislocation-free. Due to their different size and shape as compared to InAs quantum dots on planar GaAs(001), the InAs dots on GaAs(111)A nanopillars are expected to display a modified electronic structure. Strain maps evaluated by geometric phase analysis as well as by peak fitting and peak-pair analysis demonstrate a width of < 1 nm of the lattice parameter transition zone at the dislocation-free GaAs/InAs interface, indicating the effectiveness of elastic lattice relaxation at the surfaces. In the presence of dislocations a narrowing to even < 0.5 nm width is seen. Molecular statics simulations of the total energy of cylindrical axial-heteroepitaxial nanopillars with either zero or one 60° shuffle set dislocation through the centre of the heterointerface yield a larger critical diameter for misfit dislocation formation than observed experimentally, which can be attributed to a limited simulation accuracy of under-coordinated atoms along the dislocation core. A density functional theory based evaluation of the accuracy of dislocation description using Tersoff potential is subject of ongoing research.

Projektbezogene Publikationen (Auswahl)

 
 

Zusatzinformationen

© 2024 DFG Kontakt / Impressum / Datenschutz

Textvergrößerung und Kontrastanpassung