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Register a new userSuppression of threading defects formation during Sb-assisted metamorphic buffer growth in InAs/InGaAs/InP structure
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Agnieszka Gocalinska Dr
Publication date
2012
fields
Physics
and research's language is
English
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A virtual substrate for high quality InAs epitaxial layer has been attained via metalorganic vapor-phase epitaxy growth of Sb-assisted InxGa1-xAs metamorphic buffers, following a convex compositional continuous gradient of the In content from x = 53 % to 100 %. The use of trimethylantimony (or its decomposition products) as a surfactant has been found to crucially enable the control over the defect formation during the relaxation process. Moreover, an investigation of the wafer offcut-dependence of the defect formation and surface morphology has enabled the achievement of a reliably uniform growth on crystals with offcut towards the [111]B direction.
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Growth of GaAs and InGaAs nanowires by the group-III assisted Molecular Beam Epitaxy growth method is studied in dependence of growth temperature, with the objective of maximizing the indium incorporation. Nanowire growth was achieved for growth temperatures as low as 550{deg}C. The incorporation of indium was studied by low temperature micro-photoluminescence spectroscopy, Raman spectroscopy and electron energy loss spectroscopy. The results show that the incorporation of indium lowering the growth temperature does not have an effect in increasing the indium concentration in the bulk of the nanowire, which is limited to 3-5%. For growth temperatures below 575{deg}C, indium rich regions form at the surface of the nanowires as a consequence of the radial growth. This results in the formation of quantum dots, which exhibit extremely sharp luminescence.
The GaAs-based material system is well-known for the implementation of InAs quantum dots (QDs) with outstanding optical properties. However, these dots typically emit at a wavelength of around 900nm. The insertion of a metamorphic buffer (MMB) can shift the emission to the technologically attractive telecom C-band range centered at 1550nm. However, the thickness of common MMB designs limits their compatibility with most photonic resonator types. Here we report on the MOVPE growth of a novel InGaAs MMB with a non-linear indium content grading profile designed to maximize plastic relaxation within minimal layer thickness. Single-photon emission at 1550nm from InAs QDs deposited on top of this thin-film MMB is demonstrated. The strength of the new design is proven by integrating it into a bullseye cavity via nano-structuring techniques. The presented advances in the epitaxial growth of QD/MMB structures form the basis for the fabrication of high-quality telecom non-classical light sources as a key component of photonic quantum technologies.
Self-assisted growth of InAs nanowires on graphene by molecular beam epitaxy is reported. Nanowires with diameter of ~50 nm and aspect ratio of up to 100 were achieved. The morphological and structural properties of the nanowires were carefully studied by changing the substrate from bilayer graphene through buffer layer to quasi-free-standing monolayer graphene. The positional relation of the InAs NWs with the graphene substrate was determined. A 30{deg} orientation configuration of some of the InAs NWs is shown to be related to the surface corrugation of the graphene substrate. InAs NW-based devices for transport measurements were fabricated, and the conductance measurements showed a semi-ballistic behavior. In Josephson junction measurements in the non-linear regime, Multiple Andreev Reflections were observed, and an inelastic scattering length of about 900 nm was derived.
The combination of core/shell geometry and band gap engineering in nanowire heterostructures can be employed to realize systems with novel transport and optical properties. Here, we report on the growth of InAs/InP/GaAsSb core-dual-shell nanowires by catalyst-free chemical beam epitaxy on Si(111) substrates. Detailed morphological, structural, and compositional analyses of the nanowires as a function of growth parameters were carried out by scanning and transmission electron microscopy and by energy-dispersive X-ray spectroscopy. Furthermore, by combining the scanning transmission electron microscopy-Moire technique with geometric phase analysis, we studied the residual strain and the relaxation mechanisms in this system. We found that InP shell facets are well-developed along all the crystallographic directions only when the nominal thickness is above 1 nm, suggesting an island-growth mode. Moreover, the crystallographic analysis indicates that both InP and GaAsSb shells grow almost coherently to the InAs core along the 112 direction and elastically compressed along the 110 direction. For InP shell thickness above 8 nm, some dislocations and roughening occur at the interfaces. This study provides useful general guidelines for the fabrication of high-quality devices based on these core-dual-shell nanowires.
We have studied the surface modifications as well as the surface roughness of the InP(111) surfaces after 1.5 MeV Sb ion implantations. Scanning Probe Microscope (SPM) has been utilized to investigate the ion implanted InP(111) surfaces. We observe the formation of nanoscale defect structures on the InP surface. The density, height and size of the nanostructures have been investigated here as a function of ion fluence. The rms surface roughness, of the ion implanted InP surfaces, demonstrates two varied behaviors as a function of Sb ion fluence. Initially, the roughness increases with increasing fluence. However, after a critical fluence the roughness decreases with increasing fluence. We have further applied the technique of Raman scattering to investigate the implantation induced modifications and disorder in InP. Raman Scattering results demonstrate that at the critical fluence, where the decrease in surface roughness occurs, InP lattice becomes amorphous.
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