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We explore the Bi-surfactant-directed self-assembly and structure of InAs quantum dots (QDs) grown on GaAs(110) by molecular beam epitaxy. The addition of a Bi flux during InAs deposition changes the InAs growth mode from two-dimensional (2D) Frank–van der Merwe to Stranski–Krastanov (SK), resulting in the formation of three-dimensional (3D) InAs islands on the surface. Furthermore, exposing static InAs 2D layers to Bi induces a rearrangement of the strained layer into 3D islands. We explore the effect of varying the InAs thickness and Bi flux for these two growth approaches, observing a critical thickness for 3D island formation in both cases. Characterization of (110) InAs QDs with high-resolution transmission electron microscopy reveals that larger islands grown by the SK mode are plastically relaxed, while small islands grown by the on-demand approach are coherent. Strain relaxation along the [] direction is achieved by 90° pure-edge dislocations with dislocation lines running along [001]. In contrast, strain relief along [001] is by 60° misfit dislocations. This behavior is consistent with observations of planar (In, Ga)As/GaAs(110) layers. These results illustrate how surfactant Bi can provoke and control QD formation where it normally does not occur. [ABSTRACT FROM AUTHOR]

We investigate the nucleation of Ni-induced GaN nanowires by in situ and ex situ experiments. Three nucleation stages are evidenced. In the first two stages, different crystal structures of the Ni collectors are identified. Real-time monitoring of the Ga desorption allows the amount of Ga incorporated in the collectors to be quantified. A transition of their crystal structure prior to nanowire growth is found to be in agreement with the thermodynamically stable phase sequence of the relevant phase diagrams. [ABSTRACT FROM AUTHOR]

This work reports on the selectivearea growth mechanism of green-emittingInGaN/GaN nanocolumns with long InGaN sections (330–410 nm)grown by molecular beam epitaxy on GaN/sapphire. The evolution ofthe morphology of the InGaN segment is found to depend criticallyon the nominal III/V ratio as well as the diameter of the GaN section,both affecting the local III/V ratio at the top of the nanocolumn.Depending on the local III/V ratio, either metal or nitrogen rich,the diameter of the InGaN segment increases or decreases, respectively,compared to the initial diameter of the GaN segment. In addition,the In distribution inside the InGaN segment is found to depend onthe local III/V and In/Ga ratios, i.e., increasing In content towardthe top under local metal rich conditions and decreasing In contenttoward the top under locally N rich conditions. [ABSTRACT FROM AUTHOR]

Hexagonal GaN microcrystals of a size between 1 to 3 μm are obtained by the pendeoepitaxial overgrowth of a GaN nanowire template on Si(111). The GaN microcrystals are free of threading dislocations and exhibit an atomically smooth surface (roughness of 0.2 nm). Photoluminescence spectra of these microcrystals are dominated by an intense donor-bound exciton transition at 3.471 eV with a width of 1 meV reflecting strain-free GaN of exceptional structural quality. [ABSTRACT FROM AUTHOR]

Employed for a long time in optical disks, Ge2Sb2Te5is nowadays considered the most promising material also for phase-change nonvolatile memories. In the current paper, Ge–Sb–Te phase-change material thin films with a nominal composition of Ge2Sb2Te5were grown by molecular beam epitaxy on slightly mismatched GaSb and InAs substrates with (001) and (111) orientations. In situ quadrupole mass spectrometry and reflection high-energy electron diffraction allowed tight control of the growth parameters, revealing that Ge2Sb2Te5grows in epitaxial fashion only within a narrow window of substrate temperatures around 200 °C. Smooth surfaces were achieved solely on (111)-oriented substrates. Rough surfaces and interfaces were observed by transmission electron microscopy for films grown on (001)-oriented substrates. Whereas films deposited on (001) substrates possess two different vertical epitaxial orientations, single-crystalline layers exclusively (111) oriented were achieved on (111) substrates, as shown by synchrotron radiation X-ray diffraction. All the results point to the superior crystalline quality and morphology of Ge2Sb2Te5layers grown on (111) surfaces, independent of the substrate material. [ABSTRACT FROM AUTHOR]

This work focuses on homoepitaxial growth of β-Ga2O3 on (100)-oriented substrates during molecular beam epitaxy. It provides a comprehensive study on the growth mode by combining in situ with ex situ tools. In situ reflection high-energy electron diffraction (RHEED) indicates 2D layer-by-layer mode accompanied by (1 × 1) surface reconstruction. The homoepitaxial layers are grown pseudomorphic with the substrate without in-plane strain as probed by in-plane azimuthal RHEED and out-of-plane synchrotron-based high resolution x-ray diffraction. In contrast to the substrate, stacking faults and twin domains are present in the layer. [ABSTRACT FROM AUTHOR]

Employing nanofocus x-ray diffraction, we investigate the local strain field induced by a five-fold (In,Ga)N multi-quantum well embedded into a GaN micro-rod in core–shell geometry. Due to an x-ray beam width of only 150 nm in diameter, we are able to distinguish between individual m-facets and to detect a significant in-plane strain gradient along the rod height. This gradient translates to a red-shift in the emitted wavelength revealed by spatially resolved cathodoluminescence measurements. We interpret the result in terms of numerically derived in-plane strain using the finite element method and subsequent kinematic scattering simulations which show that the driving parameter for this effect is an increasing indium content towards the rod tip. [ABSTRACT FROM AUTHOR]

The ability to characterize a structure into the finest details in a quantitative manner is a key issue to understanding and controlling nanoscale phase separation in novel nanomaterials. In this work, we consider the detectability of lateral composition modulation (LCM), a type of nanoscale phase separation in GaAs1−xBix epilayers, by x-ray diffraction (XRD). We show that the satellite peaks due to LCM are hardly detectable in reasonable time with a lab x-ray diffractometer for GaAs1−xBix samples with an average x up to 25% and relative modulation up to 50%. This is in contrast to LCM reported in other III-V combinations, where the intensity of the satellite peak is relatively high and can be easily detected. Our theoretical considerations are complemented experimentally using highly brilliant synchrotron radiation. The results are in good agreement with the predictions. This work provides a guideline for the systematic characterization of LCM in zincblende III-V semiconductor epilayers and points to the critical role of quantitative characterization of nanoscale phase separation. [ABSTRACT FROM AUTHOR]

We investigated GaN-based heterostructures grown on three-dimensionally patterned Si(111) substrates by metal organic vapour phase epitaxy, with the goal of fabricating well controlled high quality, defect reduced GaN-based nanoLEDs. The high aspect ratios of such pillars minimize the influence of the lattice mismatched substrate and improve the material quality. In contrast to other approaches, we employed deep etched silicon substrates to achieve a controlled pillar growth. For that a special low temperature inductively coupled plasma etching process has been developed. InGaN/GaN multi-quantum-well structures have been incorporated into the pillars. We found a pronounced dependence of the morphology of the GaN structures on the size and pitch of the pillars. Spatially resolved optical properties of the structures are analysed by cathodoluminescence. [ABSTRACT FROM AUTHOR]