With Light-Emitting Diode Technology for Solid-State Lighting (original) (raw)
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A Novel Approach to White Light Radiation from Silicon Based Tunnel Junction LEDs
Silicon, 2020
This paper examines another kind of white light radiating half and half diode, made out of a light producing GaN/InGaN LED and a layer of semiconductor nanocrystals for shading transformation. In contrast to standard white LEDs, the gadget is arranged to accomplish high shading transformation effectiveness by means of non-radiative vitality move from the essential LED to the nanocrystals. Driven structures with sub-10 nm partition the between quantum well and the surface and designed standard brilliant LEDs are considered for the half and half gadgets, which require closeness of the nanocrystals to the quantum well. The advancement of the cross breed diode creation counting process methods for GaN LED and joining of the nanocrystals are given the accentuation on the distinctions with standard LED preparing. Results and investigation of optical and electrical portrayal counting photoluminescence (PL), smaller scale PL, time-settled PL and electroluminescence (EL) together with current-voltage qualities are exhibited to assess the gadget execution. An away form of non-radiative vitality move was found in the transporter elements of both the LED and the nanocrystals when the quantum wellnanocrystals partition was under 10 nm. Examination of the outcomes shows that in request to accomplish adequate for the white LED shading transformation, better surface passivation and nanocrystals with shorter exciton lifetimes and more vulnerable auger recombination are required.
Analysis of the green gap problem in III-nitride LEDs
2015
The green gap problem refers to the lack of high-efficacy LEDs in the green–yellow range of the visible spectrum. From the side of the III–nitride LEDs, it is caused mainly by the increase of the efficiency droop, but also in part by the increase of the electrical losses, with respect to shorter-wavelength LEDs. This study clarifies some points about the causes of the green gap. Empirical measurements of the recombination rate coefficients show that the droop aggravates with increasing wavelength mainly due to the increase of the radiative carrier lifetime with increasing wavelength. Being clear that the problem of the droop could be overcome by operating the quantum wells at lower carrier injection rates, the possibility of using an InGaN phosphor to convert the blue light of a more efficient blue LED into green light was considered. A device based on this concept was realized and its efficacy surpassed that of a traditional green LED.
Pivotal role of ballistic and quasi-ballistic electrons on LED efficiency
2010
Significant progress in the power conversion efficiency and brightness of InGaN-based light emitting diodes (LEDs) has paved the way for these devices to be considered for LED lighting. In this realm, however, the efficiency must be retained at high injection levels in order to generate the lumens required. Unfortunately, LEDs undergo a monotonic efficiency degradation starting at current densities even lower than 50 A/cm 2 which would hinder LED insertion into the general lighting market. The physical origins for the loss of efficiency retention are at present a topic of intense debate given its enormous implications. This paper reviews the current status of the field regarding the mechanisms that have been put forward as being responsible for the loss of efficiency, such as Auger recombination, electron overflow (spillover), current crowding, asymmetric injection of electrons and holes, and poor transport of holes through the active region, the last one being applicable to multiple quantum well designs. While the Auger recombination received early attention, increasing number of researchers seem to think otherwise at the moment in that it alone (if any) cannot explain the progressively worsening loss of efficiency reduction as the InN mole fraction is increased. Increasing number of reports seems to suggest that the electron overflow is one of the major causes of efficiency degradation. The physical driving force for this is likely to be the relatively poor hole concentration and transport, and skewed injection favoring electrons owing to their relatively high concentration. Most intriguingly there is recent experimental convincing evidence * Corresponding address: 134 X. Ni et al. / Superlattices and Microstructures 48 (2010) to suggest that quasi-ballistic electrons in the active region, which are not able to thermalize within the residence time and possibly longitudinal optical phonon lifetime, contribute to the carrier overflow which would require an entirely new thought process in the realm of LEDs.
Journal of Physical Chemistry C, 2014
The Energy Frontier Research Center (EFRC) for Solid-State Lighting Science (SSLS) is one of 46 EFRCs initiated in 2009 to conduct basic and use-inspired research relevant to energy technologies. The overarching theme of the SSLS EFRC is the exploration of energy conversion in tailored photonic structures. In this article we review highlights from the research of the SSLS EFRC. Major research themes include: studies of the materials properties and emission characteristics of III-nitride semiconductor nanowires; development of new phosphors and II−VI quantum dots for use as wavelength downconverters; fundamental understanding of competing radiative and nonradiative processes in current-generation, planar light-emitting diode architectures; understanding of the electrical, optical, and structural properties of defects in InGaN materials and heterostructures; exploring ways to enhance spontaneous emission through modification of the environment in which the emission takes place; and investigating routes such as stimulated emission that might outcompete nonradiative processes.
A textbook introducing the physical concepts required for a comprehensive understanding of p-n junction devices, light emitting diodes and solar cells. Semiconductor devices have made a major impact on the way we work and live. Today semiconductor p-n junction diode devices are experiencing substantial growth: solar cells are used on an unprecedented scale in the renewable energy industry; and light emitting diodes (LEDs) are revolutionizing energy e cient lighting. ese two emerging industries based on p-n junctions make a signi cant contribution to the reduction in fossil fuel consumption. Principles of Solar Cells, LEDs and Diodes covers the two most important applications of semiconductor diodes-solar cells and LEDs-together with quantitative coverage of the physics of the p-n junction. e reader will gain a thorough understanding of p-n junctions as the text begins with semiconductor and junction device fundamentals and extends to the practical implementation of semiconductors in both photovoltaic and LED devices. e treatment of a range of important semiconductor materials and device structures is also presented in a readable manner. Topics are divided into the following six chapters; • Semiconductor Physics • Th e PN Junction Diode • Photon Emission and Absorption • Th e Solar Cell • Light Emitting Diodes • Organic Semiconductors, OLEDs and Solar Cells Containing student problems at the end of each chapter and worked example problems throughout, this textbook is intended for senior level undergraduate students doing courses in electrical engineering, physics and materials science. Researchers working on solar cells and LED devices, and those in the electronics industry would also bene t from the background information the book provides.
Room Temperature Direct Band-Gap Emission from an Unstrained Ge P-I-N LED on Si
Solid State Phenomena, 2011
We present a novel Ge on Si based LED with unstrained i-Ge active region. The device operates at room temperature and emits photons with energy of 0.8 eV. It basically resembles a p-i-n structure formed on a sub-micrometer thin Ge layer. The Ge layer has been grown on Si substrate by utilizing thin virtual buffer, so it becomes stress free but with high threading dislocation density. We show that such forward biased diode generates strong emission, caused by direct band to band transition in Ge. Using an InSb based detector we were able to analyze the emission spectrum in a broad energy range. We show that at low and moderate currents, features belonging to the direct and the indirect band to band electronic transitions are present which are characteristic for Ge. Clearly dominating is the direct transition related peak. Due to the missing stress-related red shift this peak appears close to the desired communication wave length of 1.55 μm. The dependence of radiation intensity on th...
Impact of ballistic electron transport on efficiency of InGaN based LEDs
2011
Heterojunction light-emitting diodes (LEDs) based on the InGaN/GaN system have improved considerably but still suffer from efficiency degradation at high injection levels which unless overcome would aggravate LED lighting. Although Auger recombination has been proposed as the genesis of the efficiency degradation, it appears that the premise of electron overflow and non-uniform distribution of carriers in the active region being the immediate impediment is gaining popularity. The lack of temperature sensitivity and sizeable impact of the barrier height provided by an electron blocking layer and the electron cooling layer prior to electron injection into the active region suggest that the new concept of hot electrons and ballistic/quasi-ballistic transport be invoked to account for the electron overflow. The electron overflow siphons off the electrons before they can participate in the recombination process. If the electrons are made to remain in the active region e.g. by cooling them prior to injection and/or blocking the overflow by an electron blocking layer, they would have to either recombine, radiatively or nonradiatively (e.g. Shockley-Read-Hall and Auger), or accumulate in the active region. The essence of the proposed overflow model is in good agreement with the experimental electroluminescence data obtained for m-plane and c-plane LEDs with/without electron blocking layers and with/without staircase electron injectors.