Strain-Driven Growth of GaAs(111) Quantum Dots with Low Fine Structure Splitting

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting(FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters

Quantum Dot Growth on (111) and (110) Surfaces Using Tensile-Strained Self-Assembly

The self-assembly of epitaxial quantum dots on (001) surfaces, driven by compressive strain, is a widely used tool in semiconductor optoelectronics. In contrast, the growth of quantum dots on (111) and (110) surfaces has historically been a significant challenge. In most cases the strain relaxes rapidly via dislocation nucleation and glide before quantum dots can form. In this paper, we discuss a method for the reliable and controllable self-assembly of quantum dots on both (111) and (110) surfaces, where tensile strain is now the driving force. By showing that tensile-strained self-assembly is applicable to several material systems, we demonstrate the versatility of this technique. We believe that tensile-strained self-assembly represents a powerful tool for heterogeneous materials integration, and nanomaterial development, with future promise for band engineering and quantum optics applications

Two Departments, Two Models of Interdisciplinary Peer Learning

On graduation, teacher candidates (TCs) are typically underprepared to teach science, particularly physical science, whereas physics graduates frequently lack training in teaching or effective communication. In response, we created two models for interdisciplinary peer learning where TCs were paired with either graduate or undergraduate physics students. In both models, physics students teach TCs content knowledge relevant to a given area of either classical or quantum physics, which TCs then use to design and implement a short lesson for K-5 students. Overall, both models were successful, with the two sets of students reporting benefits in each case. Affordances for TCs included increased confidence to teach physical science and an appreciation for collaboration with experts. Physics students described increased awareness of the complexities of communicating science to general audiences and stronger community with their classmates. Students from both groups cited insufficient project time as a constraint, whereas physics students found it challenging to align their project and coursework. In moving away from traditional lecture, these interdisciplinary collaborations also benefitted us as instructors, giving us new perspectives on teaching. In light of our findings we propose improvements to these proof-of-concept models to enable their future scale-up and replication in other disciplines

Tissue biochemical diversity of 20 gooseberry cultivars and the effect of ethylene supplementation on postharvest life

The European gooseberry (Ribes uva-crispa) is still an understudied crop with limited data available on its biochemical profile and postharvest life. A variety of polyphenols were detected in the skin and flesh of 20 gooseberry cvs, representing mainly flavonol glycosides, anthocyanins and flavan-3-ols. In contrast, gooseberry seeds were for the first time characterised by the presence of considerable amounts of hydroxycinnamic acid glycosides tentatively identified by UPLC-QToF/MS. All cvs examined represented a good source of vitamin C while being low in sugar. Furthermore, the postharvest stability of bioactives was explored by supplementation of exogenous ethylene in air at 5 °C. Results suggest a low sensitivity of gooseberries to ethylene. The overall quality of gooseberries remained stable over two weeks, showing potential for extended bioactive life

Kinetic Monte Carlo Simulations of Quantum Dot Self-Assembly

In the Stranski–Krastanov growth mode for heteroepitaxial systems, layer-by-layer growth is followed by the formation and growth of three-dimensional (3D) islands. In this paper, we use a kinetic Monte Carlo method to simulate this growth mode behavior. We present a detailed and systematic investigation into the effects of key model parameters including strain, growth temperature, and deposition rate on this phenomenon. We show that increasing the strain lowers the apparent critical thickness that is defined by the onset of 3D island formation. Similarly, increasing the growth temperature lowers the apparent critical thickness, until intermixing, and the resulting relevance of entropic contributions, become more significant. We also report the impact on Stranski–Krastanov growth of more model-specific parameters, such as bond strengths between constituent atoms of the system, and surface energy anisotropies

Review Article: Molecular Beam Epitaxy of Lattice-Matched InAlAs and InGaAs Layers on InP (111)A, (111)B, and (110)

For more than 50 years, research into III–V compound semiconductors has focused almost exclusively on materials grown on (001)-oriented substrates. In part, this is due to the relative ease with which III–Vs can be grown on (001) surfaces. However, in recent years, a number of key technologies have emerged that could be realized, or vastly improved, by the ability to also grow high-quality III–Vs on (111)- or (110)-oriented substrates These applications include: next-generation field-effect transistors, novel quantum dots, entangled photon emitters, spintronics, topological insulators, and transition metal dichalcogenides. The first purpose of this paper is to present a comprehensive review of the literature concerning growth by molecular beam epitaxy (MBE) of III–Vs on (111) and (110) substrates. The second is to describe our recent experimental findings on the growth, morphology, electrical, and optical properties of layers grown on non-(001) InP wafers. Taking InP(111)A, InP(111)B, and InP(110) substrates in turn, the authors systematically discuss growth of both In0.52Al0.48As and In0.53Ga0.47As on these surfaces. For each material system, the authors identify the main challenges for growth, and the key growth parameter–property relationships, trends, and interdependencies. The authors conclude with a section summarizing the MBE conditions needed to optimize the structural, optical and electrical properties of GaAs, InAlAs and InGaAs grown with (111) and (110) orientations. In most cases, the MBE growth parameters the authors recommend will enable the reader to grow high-quality material on these increasingly important non-(001) surfaces, paving the way for exciting technological advances

Selective-Area Growth of Heavily \u3cem\u3en\u3c/em\u3e–Doped GaAs Nanostubs on Si(001) by Molecular Beam Epitaxy

Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth(SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growthparameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAsgrowth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grownGaAs nanostubs by fabricating heterogeneous p+–Si/n+–GaAs p–n diodes

Influence of the InAs Coverage on the Performance of Submonolayer-Quantum-Dot Infrared Photodetectors Grown with a (2×4) Surface Reconstruction

Two infrared photodetectors based on submonolayer quantum dots, having a different InAs coverage of 35% and 50%, were grown, processed and tested. The detector with the larger coverage yielded a specific detectivity of 1.13×10 11 cm Hz 1/2 W -1 at 12K, which is among the highest values reported in the literature for that kind of device

Impact of Arsenic Species on Self-Assembly of Triangular and Hexagonal Tensile-Strained GaAs(111)A Quantum Dots

We use dimeric arsenic (As2) or tetrameric arsenic (As4) during molecular beam epitaxy to manipulate the structural and optical properties of GaAs(111)A tensile-strained quantum dots (TSQDs). Choice of arsenic species affects nucleation and growth behavior during TSQD self-assembly. Previously, epitaxial GaAs(111)A TSQDs have been grown with As4, producing TSQDs with a triangular base, and \u27A-step\u27 edges perpendicular to the three 1̅1̅2 directions. We demonstrate that using As2 at low substrate temperature also results in triangular GaAs(111)A TSQDs, but with \u27B-step\u27 edges perpendicular to the three 112̅ directions. We can therefore invert the crystallographic orientation of these triangular nanostructures, simply by switching between As4 and As2. At higher substrate temperatures, GaAs(111)A TSQDs grown under As2 develop with a hexagonal base. Compared with triangular dots, the higher symmetry of hexagonal TSQDs may reduce fine-structure splitting on this (111) surface, a requirement for robust photon entanglement. Regardless of shape, GaAs(111)A TSQDs grown under As2 exhibit superior optical quality

Data Management Plan for Graduate Identity Formation Through Teaching

Data management plan for NSF Education and Human Resources (EHR) Innovations in Graduate Education (IGE) Program Proposa