Arrays of quantum-light-emitting diodes with site-controlled pyramidal quantum dots

Quantum information technology is an interdisciplinary subject, merging quantum mechanics and information science. In this field, the building blocks are quantum bits (qubits), which are superposition quantum states of simple two-level systems. Among all the platforms for the preparation of qubits, the polarization directions of single-photons are attractive as information carriers for practical realizations, due to reduced photon decoherence as well as the fact that they can be manipulated by convenient optical components. Moreover, the request for entangled sources from quantum communication and quantum computation can be satisfied by polarization-entangled photon emitters. In combination of their atomic-like energy structure and mature development in foundries/labs, epitaxial semiconductor quantum dots (QDs) have been exploited to deliver quantum light sources, such as indistinguishable single-photons and polarization-entangled photon pairs, by both optical and electrical injection (with triggering on demand). However, conventional self-assembled QDs nucleate randomly and possess finite values of finestructure splitting (FSS) in the excitonic states, mainly due to low crystal symmetry, which adds hurdles to entanglement reconstruction and significantly limits their scalability and potential for further integration. In this thesis, pyramidal QDs (PQDs) were grown by metalorganic vapor phase epitaxy (MOVPE), starting from site- controlled pyramidal recesses photolithographydefined on GaAs (111)B substrates. Their inherent properties enable them to be controlled spatially and provide them with high crystal symmetry, i.e., close-to zero FSS, suggesting an alternative for the solution of the abovementioned difficulties encountered by selfassembled QDs. However, the non-planar feature of PQDs makes it challenging to embed them into light-emitting diodes (LEDs). Here, we developed and designed a fabrication process which successfully overcame the configuration-induced processing complexity for the preparation of on demand single-photon and entangled-photon sources by electrical injection. xiv Indeed, the main achievement in this thesis is the fabrication of quantum LEDs with site-controlled PQDs which are able to generate single-photons and polarizationentangled photon pairs triggered on demand. In single-photon emission, the value of g(2) (0) could be reduced to 0.078 0.066 when combined with a time-gating technique under pulse exciation. On the other hand, the fidelities to the expected maximally polarizationentangled state were 0.85±0.04 under continuous excitation and 0.823±0.019 under pulse excitation by assistance of time-gating, with 75 % of the intensity maintained in a 1.5 ns window. The prepared entangled source was also importantly proved to violate Bell’s inequalities. Moreover we worked around finding solutions to some challenging issues concerning PQDs. The system in this study was an In0.25Ga0.75As QD sandwiched by GaAs barriers. One issue in our MOVPE-grown PQDs is a dominant negatively-charged environment. We explored a number of methods as detailed in the text which proved effective in suppressing at specific conditions the probability of capturing excess electrons, strongly improving the polarization-entangled photon pair emission via the biexcitonexciton decay process, and improving our sources. Also, a previous growth model on the AlGaAs/GaAs system developed in our group was expanded to the current system to understand the mechanism of indium segregation on both InGaAs V-grooved quantum wires and PQDs. The simulation successfully suggested consistent growth temperature-dependent emission energy evolution with the reported experimental results, in which an unexpected QD redshifting paired by a lateral quantum wires blueshifting with increasing growth temperature was observed. In addition, a new faceting at the pyramidal recess base during MOVPE growth was observed and reported for the first time. Altogether our results justify the PQD system as a promising platform to generate quantum light sources meeting a number of important requirements: e.g. spatial control, high fidelity, trigger on demand, and electrical injection

Indium segregation during III-V quantum wire and quantum dot formation on patterned substrates

We report a model for metalorganic vapor-phase epitaxy on non-planar substrates, specifically V-grooves and pyramidal recesses, which we apply to the growth of InGaAs nanostructures. This model, based on a set of coupled reaction-diffusion equations, one for each facet in the system, accounts for the facet-dependence of all kinetic processes (e.g., precursor decomposition, adatom diffusion, and adatom lifetimes) and has been previously applied to account for the temperature, concentration, and temporal-dependence of AlGaAs nanostructures on GaAs (111)B surfaces with V-grooves and pyramidal recesses. In the present study, the growth of In$_{0.12}$Ga$_{0.88}$As quantum wires at the bottom of V-grooves is used to determine a set of optimized kinetic parameters. Based on these parameters, we have modeled the growth of In$_{0.25}$Ga$_{0.75}$As nanostructures formed in pyramidal site-controlled quantum-dot systems, successfully producing a qualitative explanation for the temperature-dependence of their optical properties, which have been reported in previous studies. Finally, we present scanning electron and cross-sectional atomic force microscopy images which show previously unreported facetting at the bottom of the pyramidal recesses that allow quantum dot formation.Comment: 9 pages, 8 figure

Statistical study of stacked/coupled site-controlled pyramidal quantum dots and their excitonic properties

We report on stacked multiple quantum dots (QDs) formed inside inverted pyramidal recesses, which allow for the precise positioning of the QDs themselves. Specifically, we fabricated double QDs with varying inter-dot distances and ensembles with more than two nominally highly symmetric QDs. For each, the effect of the interaction between QDs is studied by characterizing a large number of QDs through photoluminescence spectroscopy. A clear red-shift of the emission energy is observed together with a change in the orientation of its polarization, suggesting an increasing interaction between the QDs. Finally, we show how stacked QDs can help influencing the charging of the excitonic complexes

A site-controlled quantum dot light-emitting diode of polarization-entangled photons, violating Bell's inequality

The first site-controlled quantum dot light-emitting diode of non-classical light - single and polarization-entangled photons - violating Bell's inequality is presented in this work. The diode structure is based on highly symmetric, single, site-controlled pyramidal quantum dots

On-demand single-photons from electrically-injected site-controlled pyramidal quantum dots

We report on the performance of electrically-injected pyramidal quantum dots (PQDs) in terms of single-photon emission. We previously presented the generation of entangled photon pairs from similarly structured devices. Here we show that it is also possible to obtain single-photons upon continuous wave excitation as well as pulsed excitation, obtaining a low g 2 (0) of 0.088  ±  0.059, by discarding re-excitation events within a single excitation pulse by applying time-gating techniques

Enhanced Antifungal Bioactivity of Coptis Rhizome Prepared by Ultrafining Technology

The aim of this study was to identify and quantify the bioactive constituents in the methanol extracts of Coptis Rhizome prepared by ultrafining technology. The indicator compound was identified by spectroscopic method and its purity was determined by HPLC. Moreover, the crude extracts and indicator compound were examined for their ability to inhibit the growth of Rhizoctonia solani Kühn AG-4 on potato dextrose agar plates. The indicator compound is a potential candidate as a new plant derived pesticide to control Rhizoctonia damping-off in vegetable seedlings. In addition, the extracts of Coptis Rhizome prepared by ultrafining technology displayed higher contents of indicator compound; they not only improve their bioactivity but also reduce the amount of the pharmaceuticals required and, thereby, decrease the environmental degradation associated with the harvesting of the raw products

Eliminating temporal correlation in quantum-dot entangled photon source by quantum interference

Semiconductor quantum dots, as promising solid-state platform, have exhibited deterministic photon pair generation with high polarization entanglement f\textcompwordmark idelity for quantum information applications. However, due to temporal correlation from inherently cascaded emission, photon indistinguishability is limited, which restricts their potential scalability to multi-photon experiments. Here, by utilizing quantum interferences to decouple polarization entanglement from temporal correlation, we improve multi-photon entanglement f\textcompwordmark idelity from $(58.7\pm 2.2)\%$ to $(75.5\pm 2.0)\%$. Our work paves the way to realize scalable and high-quality multi-photon states from quantum dots

Induction chemotherapy with dose-modified docetaxel, cisplatin, and 5-fluorouracil in Asian patients with borderline resectable or unresectable head and neck cancer

BackgroundSignificant ethnic differences in susceptibility to the effects of chemotherapy exist. Here, we retrospectively analyzed the safety and efficacy of induction chemotherapy (ICT) with dose-modified docetaxel, cisplatin, and 5-fluorouracil (TPF) in Asian patients with borderline resectable or unresectable head and neck squamous cell carcinoma (HNSCC).MethodsBased on the incidence of adverse events that occurred during daily practice, TPF90 (90% of the original TPF dosage; docetaxel 67.5 mg/m2 on Day 1, cisplatin 67.5 mg/m2 on Day 1, and 5-fluorouracil 675 mg/m2 on Days 1–5) was used for HNSCC patients who were scheduled to receive ICT TPF.ResultsBetween March 2011 and May 2014, 52 consecutive patients with borderline resectable or unresectable HNSCC were treated with ICT TPF90 followed by concurrent chemoradiotherapy. Forty-four patients (84.6%) received at least three cycles of ICT TPF90. The most commonly observed Grade 3–4 adverse events included neutropenia (35%), anemia (25%), stomatitis (35%), diarrhea (16%), and infections (13.5%). In an intention-to-treat analysis, the complete and partial response rates after ICT TPF90 were 13.5% and 59.6%, respectively. The complete and partial response rates following radiotherapy and salvage surgery were 42.3% and 25.0%, respectively. The estimated 3-year overall survival and progression-free survival rates were 41% [95% confidence interval (CI): 25–56%] and 23% (95% CI: 10–39%), respectively. The observed median overall survival and progression-free survival were 21.0 months (95% CI: 13.3–28.7 months) and 16.0 months (95% CI: 10.7–21.3 months), respectively.ConclusionTPF90 is a suitable option for Asian patients with borderline resectable or unresectable HNSCC who are scheduled for ICT