Efficiency Models for GaN-based Light-Emitting Diodes: Status and Challenges

Light emitting diodes (LEDs) based on Gallium Nitride (GaN) have been revolutionizing various applications in lighting, displays, medical equipment, and other fields. However, their energy efficiency is still below expectations in many cases. An unprecedented diversity of theoretical models has been developed for efficiency analysis and GaN-LED design optimization. This review paper provides an overview of the modeling landscape and pays special attention to the influence of III-nitride material properties. It thereby identifies some key challenges and directions for future improvements.Comment: submitted to MDPI Material

Build Technological procedures groundworks and foundational constructions

PIPREK, Petr. Stavebně technologický postup provádění zemních prací a základových konstrukcí. VŠB-Technická univerzita Ostrava, Fakulta stavební, Katedra pozemního stavitelství, 2019, 66 s. Řešením mé bakalářské práce je vypracování projektové dokumentace bytového domu se 14-ti startovacími byty. Nosné konstrukce domu jsou navrženy z komplexního systému POROTHERM. Dům je navržen jako nepodsklepený se čtyřmi nadzemními podlažími a plochou střechou. V přízemní se nacházejí dvě bytové jednotky a z toho je jedna řešena pro osoby se sníženou či omezenou pohyblivostí a dále pak technické zázemí, společné prostory a sklepní boxy. V dalších podlažích jsou vždy čtyři bytové jednotky. Předmětem mé bakalářské práce je vypracování technologického postupu provedení zemních prací a základových konstrukcí včetně vypracování časového plánu těchto prací a stanovení orientační ceny. Bakalářská práce obsahuje textovou i výkresovou část dokumentace stavby.PIPREK, Petr. Construction and Technological Process of Implementation of groundworks and base constructions. VŠB-Technical University of Ostrava, Faculty of Civil Engineering, Department of Building Constructions, 2019, 66 p. The solution of my bachelor thesis is the project documentation development for a residential building with 14 startup flats. The supporting structures of the house are designed from a complex POROTHERM system. The house is designed as a non-basement with four above-ground floors and a flat roof. On the ground floor, there are two dwelling units, one of which is designed for people with reduced or limited mobility. Further, there are technical facilities, common areas (hall/lobby) and storage units. On each of the other floors, there are always four dwelling units. The subject of my bachelor thesis is the elaboration of the technological process of execution of earthworks and foundation constructions, including preparation of the time schedule of work and defining the price budget. The bachelor thesis contains both the text and drawing part of the building documentation.225 - Katedra pozemního stavitelstvívýborn

Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As

The magnetic properties of the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As are studied within the dynamical cluster approximation. We use the k-dot-p Hamiltonian to describe the electronic structure of GaAs with spin-orbit coupling and strain effects. We show that nonlocal effects are essential for explaining the experimentally observed transition temperature and saturation magnetization. We also demonstrate that the cluster anisotropy is very strong and induces rotational frustration and a cube-edge direction magnetic anisotropy at low temperature. With this, we explain the temperature-driven spin reorientation in this system.Comment: 4 pages, 4 figures; to be published in Phys. Rev. Let

Genetyczne podłoże zaburzeń determinacji płci i rozwoju gonad

Intersexual disorders, the causes of which are frequently difficult to diagnose, usually result from the disruption of sex determination and gonadal development or from impairment in function of endocrine organs such as gonads and adrenal glands. Thus consideration of etiopatogenesis of intersexuality should be based on an analysis of the genetic control of sex determination, gonadal differentiation and first of all molecular regulation of steroidogenic cell differentiation and functioning. These processes take place in the fetal gonads, which explains the small amount of data concerning the development of human gonads. However, numerous investigations of gene expression in murine gonads have revealed a complicated machinery involved in sex determination and gonadal differentiation. Moreover, data obtained from mice have led to a better understanding of the molecular background of sex determination and gonad differentiation in humans. Nevertheless, the interpretation of mouse gene knock-outs does not always reflect mutations of their homologues in man. This article compares data in humans and mice, revealing the existence of many sex-determining genes in both, which should be taken into consideration during the diagnosis of intersexual disorders. Mutations of some genes controlling murine gonad development have not been described in humans so far. This indicates the necessity of conducting extensive genetic analysis of individuals with intersexual disorders.Zaburzenia interseksualne, których przyczyny są często trudne do zdiagnozowania, zazwyczaj wynikają z nieprawidłowości w determinacji płci i rozwoju gonad lub z zaburzeń funkcji endokrynnych tych organów. Dlatego zrozumienie etiopatogenezy interseksualizmu powinno się opierać na analizie genetycznej kontroli determinacji płci, różnicowania gonad oraz przede wszystkim kontroli różnicowania się i funkcji komórek steroidogennych w gonadach. Powyższe procesy zachodzą w gonadach zarodków, co ma związek z niewielką ilością danych dotyczących rozwoju gonad ludzkich. Istnieją jednak liczne badania ekspresji genów w gonadach myszy, które ujawniły udział wielu genów kluczowych dla determinacji i różnicowania się gonad. Badania przeprowadzone na myszach zdecydowanie pozwoliły lepiej zrozumieć molekularne podłoże determinacji i różnicowania płci człowieka, chociaż skutki wyłączenia ekspresji tych genów u myszy nie zawsze w pełni odpowiadają przypadkom mutacji ich homologicznych genów u ludzi. Niniejszy artykuł stanowi zestawienie wyników badań ujawniających istnienie wielu genów decydujących o płci zarówno człowieka, jak i myszy, na które powinno się zwrócić uwagę podczas diagnozowania zaburzeń interseksualnych u ludzi. Dotychczas nie opisano u ludzi mutacji niektórych genów kontrolujących rozwój gonad u myszy. Sugeruje to konieczność podjęcia prób szerszej analizy genetycznej osób z zaburzeniami interseksualnymi

InGaN/GaN disk-in-nanowire white light emitting diodes on (001) silicon

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98666/1/ApplPhysLett_98_193102.pd

Index-antiguiding in narrow-ridge GaN-based laser diodes investigated by measurements of the current-dependent gain and index spectra and by self-consistent simulation

The threshold current density of narrow (1.5 {\mu}m) ridge-waveguide InGaN multi-quantum-well laser diodes, as well as the shape of their lateral far-field patterns, strongly depend on the etch depth of the ridge waveguide. Both effects can be attributed to strong index-antiguiding. A value of the antiguiding factor R = 10 is experimentally determined near threshold by measurements of the current-dependent gain and refractive index spectra. The device performances are simulated self-consistently solving the Schr\"odinger-Poisson equations and the equations for charge transport and waveguiding. Assuming a carrier-induced index change which matches the experimentally determined antiguiding factor, both the measured high threshold current and the shape of the far-field pattern of lasers with shallow ridges can be reproduced theoretically.Comment: This is an author-created, un-copyedited version of an article accepted for publication in the IEEE Journal of Quantum Electronics. IEEE is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Yield and leakage currents of large area lattice matched InP/InGaAs heterostructures

Demonstrating and harnessing electroluminescent cooling at technologically viable cooling powers requires the ability to routinely fabricate large area high quality light-emitting diodes (LEDs). Detailed information on the performance and yield of relevant large area devices is not available, however. Here, we report extensive information on the yield and related large area scaling of InP/InGaAs LEDs and discuss the origin of the failure mechanisms based on lock-in thermographic imaging. The studied LEDs were fabricated as mesa structures of various sizes on epistructures grown at five different facilities specialized in the growth of III-V compound semiconductors. While the smaller mesas generally showed relatively good electrical characteristics and low leakage current densities, some of them also exhibited unusually large leakage current densities. The provided information is critical for the development and design of the optical cooling technologies relying on large area devices.Peer reviewe

GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 μm operation

Hot electron light emission and lasing in semiconductor heterostructure (Hellish) devices are surface emitters the operation of which is based on the longitudinal injection of electrons and holes in the active region. These devices can be designed to be used as vertical cavity surface emitting laser or, as in this study, as a vertical cavity semiconductor optical amplifier (VCSOA). This study investigates the prospects for a Hellish VCSOA based on GaInNAs/GaAs material for operation in the 1.3-μm wavelength range. Hellish VCSOAs have increased functionality, and use undoped distributed Bragg reflectors; and this coupled with direct injection into the active region is expected to yield improvements in the gain and bandwidth. The design of the Hellish VCSOA is based on the transfer matrix method and the optical field distribution within the structure, where the determination of the position of quantum wells is crucial. A full assessment of Hellish VCSOAs has been performed in a device with eleven layers of Ga0.35In0.65N0.02As0.08/GaAs quantum wells (QWs) in the active region. It was characterised through I-V, L-V and by spectral photoluminescence, electroluminescence and electro-photoluminescence as a function of temperature and applied bias. Cavity resonance and gain peak curves have been calculated at different temperatures. Good agreement between experimental and theoretical results has been obtained