Physics of Optoelectronics
The results will help to overcome the effect of unwanted doping, and to distinguish between different recombination loss mechanisms in these important photovoltaics. Hybrid organic-inorganic heterojunctions have emerged as low-cost alternatives for fabricating optoelectronic devices, but their charge-transport mechanism has not been fully established. This study provides physical insight into the interpretation of the characteristic current-voltage curves of these and similar hybrid devices.
In solar-cell technology, band-gap grading has been introduced to enhance the efficiency of charge collection, by inducing drift motion of charge carriers. Characterizing such systems accurately is tricky, though, due to technical difficulty in clearly separating carrier diffusion from drift. This study uses wavelength-dependent lateral photocurrent in a generic device structure to simultaneously characterize the electrical qualities of both the light absorber and the back surface in a graded-band-gap solar cell.
The technique is readily applicable to many types of photoactive devices, because it works well without any knowledge of the actual band-gap grading. Although quantum key distribution QKD promises information-theoretic security, several studies have been carried out showing how its security can be compromised by targeting the detectors in the system. This work demonstrates a measure to mitigate a special class of attack, the a f t e r g a t e a t t a c k.
By exploiting delayed detection events, which are usually considered detrimental for QKD, the authors show how an eavesdropper mounting such an attack can be unveiled. The maximum conversion efficiencies of photovoltaic devices and performance-limiting factors of practical solar cells remain ambiguous, and thus the strict determination of current technological limits is of significant importance.
This study develops an analytical scheme that allows the evaluation of realistic maximum-power conversion efficiencies of important inorganic and hybrid perovskite solar cells in conventional thin-film form. The authors study the photoresponse of a broadband THz-frequency detector with stepped quantum wells in the absorption layer.
Due to the asymmetric distribution of the wave function of the second excited subband E 2 , the escape probability for photoexcited electrons is strongly dependent on bias polarity, which is responsible for the different shapes of photocurrent spectra under positive and negative bias voltages. These results show that not only band structure but also the nature of the wave function itself plays a key role in designing these high-performance quantum-well photodetectors.
Injection locking replicates the frequency and phase of a driven oscillator in a target oscillator, with applications in electronic, mechanical, and optical systems, and lately in mesoscopic circuits.
The technique requires the driven oscillator to be almost resonant with the target oscillator. This study uses a superconducting circuit to demonstrate injection locking in a well-controlled parametric microwave oscillator. The authors furthermore present another technique, p a r a m e t r i c l o c k i n g , that removes the constraint on detuning between the oscillators. This should impact any device that should not or cannot be close to resonant driving, as in quantum information processing.
Photochemical upconversion is a means to turn light that a solar cell cannot use into light that it can use, and thus could boost efficiency beyond the Shockley-Queisser limit. So far, though, it has not been possible to quantitatively predict the increased photocurrent. The authors use ray optics and exciton kinetics to compute a figure of merit that directly reflects solar-cell performance. They furthermore illustrate the applications of these methods to device design, by investigating the performance penalty imposed by Boltzmann statistics.
Quantum yield QY is an essential parameter for the optical characterization of light-emitting materials, for applications in e. This study points out a systematic bias present in standard QY methodology for samples with lower absorption. The bias manifests itself as an absorption-dependent underestimation of QY, and might lead to misinterpretation of QY dependences on parameters that are linked to absorption, such as the excitation wavelength.
This work addresses that bias and offers a correction procedure, and thus could have dramatic impact on a great number and variety of applications. Engineering and understanding microwave resonators is essential for the efficient electron-spin control and readout in electron-spin-resonance ESR spectroscopy. This work, focused on superconducting planar microresonators, presents finite-element simulations modeling the spin-photon coupling rate, in quantitative agreement with experimental data.
Imaging techniques using nitrogen-vacancy centers in diamond are appealing for characterizing two-dimensional devices and materials, but their compatibility with gated devices is largely unexplored. Current densities in the device are mapped at different doping conditions, and substantial modulation of the electric field at the diamond surface is seen, suggesting a complex electrostatic response of the multilayered structure. Pathways to mitigate the invasiveness of the imaging technique are discussed.
Implanting gold ions in silicon at concentrations far higher than the equilibrium solubility limit promotes sub-band-gap optical absorption, and thus has been explored in the context of Si-based near-infrared photodetectors. This absorption enhancement decreases after annealing, though, according to the structural relaxation of the material. In this article, the evolution of composition and structure of Au-hyperdoped Si after thermal relaxation is investigated in detail.
The results provide crucial information for fabricating devices using Au-hyperdoped Si, and may also pertain to other hyperdoped impurities. Color centers in diamond are considered one of the most promising platforms for electrically driven single-photon sources operating under ambient conditions. Efficient electrical excitation of these emitters is challenging, due to the extremely high activation energy of donors in diamond, which limits the density of free electrons.
It may possible to overcome this doping limit, though. Electro-optical effects in nematic liquid crystals are extensively used in display technology.
A major drawback that has hindered further application is the relatively slow time of the optical response to an applied field, on the order of milliseconds. The authors demonstrate a m i c r o s e c o n d -scale electro-optical response, by using the electric field to change the orientational order of a liquid crystal with giant positive dielectric anisotropy.
This phenomenon could be exploited in fast electro-optical shutters, phase modulators, beam steering, and more. The model developed here provides an improved avenue for analysis and design of graphene-based devices. Compositional variation in In,Ga N alloys is a controversial topic, still debated in the literature for its influence on the performance of light-emitting diodes.
This study accounts for the presence of nanometer-scale indium clustering in an LED, and describes its impact on the optical properties of the device. Clustering induces substantial redshift and broadening of the emission spectrum; furthermore, the temperature dependence of the radiative coefficient derived for the nonuniform structures is in good agreement with experiments that show a trend opposite that expected from standard theoretical considerations. Improving the coherence of superconducting qubits is a crucial step toward the goal of fault-tolerant quantum processors based on them.
An ongoing experimental challenge is to diagnose and mitigate the dominant decoherence mechanisms. Furthermore, the measurement technique is relevant for ultralow-noise sensing in general.
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Charge injection and collection in organic optoelectronic devices are highly sensitive to the dielectric properties of the commonly used transparent electrodes. This characteristic has been somewhat overlooked, though, as experimental results can be adequately fitted by tuning other device parameters.
This study introduces a correction to charge injection from the transparent electrode into the organic layer, which is found both experimentally and theoretically to cause a drastic reduction in the injected current. The authors argue that this characteristic must be considered in designing electrodes, and also must be included in models and parameter analysis to obtain reliable results. For perovskite semiconductors, photon recycling is relatively unexplored, especially for devices under operating conditions.
The authors develop a model to quantify the extent of photon recycling in state-of-the-art perovskite solar cells of varying nonradiative loss and geometry. They present clear experimental targets for material optoelectronic quality to harness photon recycling in solar cells, with major implications for achieving low-threshold lasing and efficient LEDs. The optical response of a two-dimensional material is given by its in-plane optical-conductivity tensor, which can be anisotropic.
- Physics of Optoelectronics (Optical Engineering) by Michael A. Parker
This work shows that atomically thin black phosphorus can be efficiently tuned to become hyperbolic over the entire visible spectrum into the ultraviolet, via bias voltage, strain, number of layers, or optical pumping. This approach will enable actively modulated nanophotonics and optoelectronics for sensing, wavefront control, nanoscale heat transfer, and enhancement of spontaneous-emission rate.
Subject ALL. Optoelectronics Semiconductor Physics Energy Research Photonics Superconductivity Quantum Information Nanophysics Plasmonics Materials Science Goals The goal of the course is to provide the tools for the understanding and design of elementary optoelectronic devices Photodetectors, Laser Diodes, LEDs.
Content Interaction between photons and a semiconductor: band to band transitions leading to absorption, spontaneous and stimulated emission of electromagnetic waves. Tests the assessment is carried-out through an open-book exam. Additional Information Course list. Contact Site plan Credits Privacy Statement.
Continuous Assessment E. Assignment, Presentation, Mid-term, etc. A two-hour final examination. When offered. Second semester. Course Syllabus The course will mainly cover the below topics: 1.
- Semiconductor devices for optoelectronics - 5PMNOSC1 - PHELMA?
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