Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

Ranasinghe, Leonardo; Heyn, Ch.; Deneke, K.; Zocher, Michael; Korneev, Roman; Hansen, W.

doi:10.3390/nano11030690

Cited by 4 publications

(2 citation statements)

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“…In addition, exciton annihilation can take place via thermal escape of charge carriers from a QD (see Equations ( 2) and ( 3)), which is already addressed in ref. [18]. The rate of thermal escape is described by…”

Section: Exciton Annihilationmentioning

confidence: 99%

“…However, with increasing temperature T, a broadening of the QD excitonic lines is reported as well as the formation of phonon sidebands [7][8][9][10][11]. Furthermore, a substantial degradation of the intensity of the emission from various types of the QDs at higher temperatures is observed [7,8,[12][13][14][15][16][17][18]. Both effects seriously interfere with an application of QDs in optical quantum information technology at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Temperature-Enhanced Exciton Emission from GaAs Cone–Shell Quantum Dots

Heyn,

Ranasinghe,

Deneke

et al. 2023

Nanomaterials

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The temperature-dependent intensities of the exciton (X) and biexciton (XX) peaks from single GaAs cone–shell quantum dots (QDs) are studied with micro photoluminescence (PL) at varied excitation power and QD size. The QDs are fabricated by filling self-assembled nanoholes, which are drilled in an AlGaAs barrier by local droplet etching (LDE) during molecular beam epitaxy (MBE). This method allows the fabrication of strain-free QDs with sizes precisely controlled by the amount of material deposited for hole filling. Starting from the base temperature T = 3.2 K of the cryostat, single-dot PL measurements demonstrate a strong enhancement of the exciton emission up to a factor of five with increasing T. Both the maximum exciton intensity and the temperature Tx,max of the maximum intensity depend on excitation power and dot size. At an elevated excitation power, Tx,max becomes larger than 30 K. This allows an operation using an inexpensive and compact Stirling cryocooler. Above Tx,max, the exciton intensity decreases strongly until it disappears. The experimental data are quantitatively reproduced by a model which considers the competing processes of exciton generation, annihilation, and recombination. Exciton generation in the QDs is achieved by the sum of direct excitation in the dot, plus additional bulk excitons diffusing from the barrier layers into the dot. The thermally driven bulk-exciton diffusion from the barriers causes the temperature enhancement of the exciton emission. Above Tx,max, the intensity decreases due to exciton annihilation processes. In comparison to the exciton, the biexciton intensity shows only very weak enhancement, which is attributed to more efficient annihilation processes.

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Section: Exciton Annihilationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Temperature-Enhanced Exciton Emission from GaAs Cone–Shell Quantum Dots

Heyn,

Ranasinghe,

Deneke

et al. 2023

Nanomaterials

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Design and operation of a portable micro-photoluminescence spectrometer for education on semiconductor quantum structures and graphene sheets

Heyn

2021

Review of Scientific Instruments

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The design and operation of a portable micro-photoluminescence spectrometer for applications in education is described. Guidelines are a compact, robust, portable, and flexible design; operation without cryogenic media for sample cooling; and a limited budget. Targeted samples are semiconductor quantum structures emitting in a wavelength range of 600–1000 nm and graphene sheets. The portable spectrometer includes a reflected-light microscope with a motorized sample stage of 156 nm step size, a thermoelectric sample cooler allowing temperatures down to 196 K, a green and a blue laser for focused excitation, a monochromator with 0.18 nm spectral resolution, and a cooled camera as the image sensor. For demonstration of the capabilities of the spectrometer, measurements of the quantized energy levels of molecular beam epitaxy grown GaAs quantum dots (QDs) are shown. Here, different sample designs are used, the sample temperature as well as the laser excitation power and energy is varied, and the respective influence on the measurements is discussed. A clear QD shell structure with four states is shown for a sample, where approximately four QDs are directly excited by a focused laser. Limitations of the spectrometer for QD characterization mainly due to the waiver of cryogenic media for sample cooling are discussed. As a further example, which does not require sample cooling, local Raman spectroscopy of a graphene sheet is demonstrated where clear Raman signatures allow the identification of a single-layer thickness.

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Exploring the Role of Nanotherapeutics for Diagnosis and Treatment of Solid Tumor

Kaushik

Verma

Akhter

et al. 2024

CNANO

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Background: Tumors are increasingly heterogeneous throughout the process of their growth, producing a mixed-cell community with a range of molecular features and susceptibility to therapies. Nanotechnology has shown tremendous potential in diagnosing and treating solid tumors. Objective: Most cancer-related deaths are attributed to the lack of early detection and effective treatment. Its early diagnosis helps overall survival and health-related quality of life in patients identified with cancer. Nanosystems are favorable for endocytic intracellular retention, high drug loading, enhanced therapeutic efficacy, greater drug-circulation time, superior dose scheduling for patient compliance, and site-specific targeting. Integrating nanosystems into biomedical applications will also reintroduce medicines that are no longer used in clinical practice because of certain drawbacks and help the identification of new active medicines with their sub-optimal kinetic profiles. This review provides insights about the targeted cancer treatment based on active targeting (folate receptor-α, heat shock protein, receptor 2 for epidermal human growth factor, and CD44 receptor) and various nano device-based systems. Methodology: The highly relevant articles were retrieved using various search engines, including Web of Sciences, Science Direct, Scihub, PubMed, Scopus, PubChem, Google Scholar, and others. The keywords and phrases used for the search are “liposomes,” “quantum dots,” “nanoparticles,” “nanocrystals,” “photodynamic therapy,” “passive targeting,” “active targeting,” “nanomaterials,” “nanotechnology,” “cancer,” “nanotheranostics” and several others. In this review, we briefly introduced the concept of the contribution of nanotheranostics to cancer therapy with their recent findings. We also discuss the role of biosensor-based nanosystems in cancer. Conclusion: Conclusion: This review addresses nanotechnology’s exciting role in identifying, imaging, and managing solid tumors and their immense potential.

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Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

Cited by 4 publications

References 45 publications

Temperature-Enhanced Exciton Emission from GaAs Cone–Shell Quantum Dots

Temperature-Enhanced Exciton Emission from GaAs Cone–Shell Quantum Dots

Design and operation of a portable micro-photoluminescence spectrometer for education on semiconductor quantum structures and graphene sheets

Exploring the Role of Nanotherapeutics for Diagnosis and Treatment of Solid Tumor

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