Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

Abstract

We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60° dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.

Defect creation in InGaAs/GaAs multiple quantum wells–I. Structural properties

“…Symmetrical (004) and asymmetrical (224) ω-2θ/ω TC reciprocal space maps (RSM) revealed the spatial distribution of diffuse scattered radiation, and hence showed structural features of the created defects. Asymmetric RSMs enable estimates to be made of the extent of relaxation of initial elastic stress, and correct specification of the preferred type of crystal defects [10][11][12].…”

“…In TC geometry, an analyzer crystal in front of the x-ray detector is used to spatially separate coherent and diffuse scattered radiation. Shape, position, and fullwidth-at-half-maximum (FWHM) of diffraction peaks in respective RCs were examined to obtain structural information about the substrate and the epitaxial layers to suggest the type, density, and spatial location of the crystal defects resulting from epitaxial growth [10][11][12][14][15][16]. Symmetrical (004) and asymmetrical (224) ω-2θ/ω TC reciprocal space maps (RSM) revealed the spatial distribution of diffuse scattered radiation, and hence showed structural features of the created defects.…”

“…Observations are interpreted in the framework of a model describing defect creation as a multi-stage process, starting from accommodation of initial elastic stress and point defect (PD) creation on the growth front, followed by inward diffusion and accumulation at pre-dislocation clusters, and finally transformation to extended defects in the volume of epitaxial structure [10][11][12]. The crystalline properties of these structures as dependent on growth conditions are related to optical properties in the companion paper [13].…”

Defect Creation in InGaAs/GaAs Multiple Quantum Wells – II. Optical Properties

“…This finding was explained as a cumulative deterioration effect. Denser creation of edge segments close to substrate/epi-structure interface (tertiary DLs) giving rise to stress relaxation [19][20][21] accounts for the denser distribution of defect states involved in SRH-recombination.…”

Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

“…[8][9][10] But few reports on the use of metamorphic grades for epitaxial nanostructures, which may offer solutions to next-generation device concepts, 11 are available. [12][13][14] Lifting the restriction of lattice-matching allows, for example, access to particular bandgaps or band offsets, while tailoring the compositional grade enables independent adjustment of strain to affect nanostructure formation. Lattice mismatch is critical to many self-assembled, epitaxial nanostructures, as it is the coherency strain inherent to these systems that often drives organization into non-planar morphology, such as in Stranski-Krastanov growth mode, in which formation of a 2-D wetting layer precedes the development of 3-D islands.…”