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Misfit Strain Relaxation by Dislocations in InAs Islands and Layers Epitaxially Grown on (001)GaAs Substrates by MOVPE
Author(s) -
Wagner G.
Publication year - 1998
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/(sici)1521-4079(1998)33:5<681::aid-crat681>3.0.co;2-p
Subject(s) - dislocation , condensed matter physics , metalorganic vapour phase epitaxy , materials science , epitaxy , relaxation (psychology) , monolayer , crystallography , strain (injury) , partial dislocations , molecular beam epitaxy , layer (electronics) , chemistry , nanotechnology , physics , medicine , psychology , social psychology
The misfit dislocation configurations in InAs islands as well as in more or less continuous layers grown on (001) oriented GaAs substrates were studied by weak‐beam and high‐resolution electron microscopy. The islands are confined by {101} and {111} facets where the aspect ratio (height/lateral extension) can be affected by the growth conditions. It is possible to grow well‐defined islands as well as relatively continuous layers by MOVPE under As‐stabilized conditions. At constant deposition parameters the growth is characterized by islands of different sizes (but with constant aspect ratio) in various strain states depending on their dislocation content. Coherently strained islands without any dislocation can be observed for heights up to 23 ML InAs, or otherwise, up to a maximal island extension of about 12 nm (for the particular aspect ratio ≈0.585). With further increase of island height and lateral extension, the introduction of dislocations becomes favourable. Independent of the island size, the layer thickness and the dislocation density, a residual elastic strain of about ε r = —0.8% remains after relaxation. This means, about 88% of the total misfit strain of ε = —6.686 × 10 —2 were compensated by Lomer dislocations. These sessile Lomer dislocations lie in the island interior only, where single 60° dislocations were observed exclusively in their near‐edge regions. With increasing island size and/or layer thickness some close‐spaced 60° dislocations occur additionally within the interfacial region. The Lomer dislocations that are always located 4 monolayers (ML) above the InAs/GaAs interfacial plane result from the well‐known fusion of two 60° slip dislocations. These 60° dislocations have been nucleated 7 … 8 ML above the interface at surface steps on the {111} facets confining the islands. Based on our experimental observations a new mechanism is proposed that explains the origin of these 60° dislocations. Their further fusion to sessile Lomer dislocations that compensate the misfit strain most efficiently occurs in the way as commonly accepted.