1,720,982 research outputs found
Characteristics of optoelectronic devices and their manufactory technology overview.
No full textCharacteristics of Optoelectronic Devices and Their Manufactory Technology Overview
Application of noise cross-correlation analysis method for reliability investigation of different wavelength light-emitting diodes.
No full textDeividas Žiūraitis APPLICATION OF THE NOISE CROSS - CORRELATION ANALYSIS METHOD FOR RELIABILITY INVESTIGATION OF DIFFERENT WAVELENGTH LIGHT – EMITTING DIODES Summary An LED is a semiconductor highly doped pn junction that, when connected in a direct direction, can emit incoherent radiation from infrared to ultraviolet. LEDs are used very widely. For example: they are used in monitors, optical communication, lighting. Although LEDs are long-lasting, their characteristics change during operation, such as: noise, voltammetric characteristics or radiated power etc. Their internal structure also changes, and as they age, additional defects appear. It is well known that noise research provides valuable information about the physical processes that take place in semiconductor materials and structures and is useful in assessing the quality of semiconductor devices. The aim of this work was to measure the noise, spectral and electrical characteristics of InGaN white LEDs and to evaluate the reliability of the devices during the aging experiment using the correlation analysis method. During the work, two white LEDs were examined. After examining the noise characteristics of LEDs, it was found that the spectrum of electrical fluctuations of both samples consists of 1/f type, pulsed and generating recombinant noise components. The spectrum of optical fluctuations of the studied samples consists of 1/f nature and white noise components. Theoretical evaluations showed that the low-frequency optical and electrical fluctuations in the studied LEDs at low currents were correlated completely. This indicates that the noise sources are located in the active area of the LEDs. At high currents, additional noise sources were observed, which affect electrical and optical fluctuations differently
Noise spectroscopy of n-based and p-based leds.
No full textNoise Spectroscopy of N-based and P-based LEDs
Noise spectroscopy of light–emitting and laser diodes.
No full textNoise Spectroscopy of Light–Emitting and Laser Diodes
Low-frequency noise spectroscopy of single-mode and multimode laser diodes.
No full textLaser diodes (LDs) are compact forward biased pn junction devices. Mid-infrared spectral region 2-3 µm is considered to be “eye-safe” and multimode Fabry–Perot GaInAsSb LDs, operating in this region, are used in the field of gas sensing, medical and defense applications. Single-mode distributed feedback (DFB) InGaAsP lasers have a huge significance in the high-speed optical communication systems as they can guarantee narrow and stable spectrum of the light what enables higher transmission speed and higher data rate. Low-frequency noise spectroscopy, which is used for these lasers analysis, is nondestructive and very sensitive diagnostic tool for optoelectronic device quality evaluation and identification of nature of the degradation sources. It is well known that excess noise in semiconductor device is caused by defects and structural nonidealities. The aim of this work was to investigate DFB and FP LDs low-frequency noise characteristics, to find their relation with the device quality and reliability, to present a detailed analysis of electrical and optical fluctuations of LD by correlation method and to demonstrate various methods for laser threshold identifying. Investigated DFB laser diodes are distinguished by 1/f α-type optical and electrical fluctuations at the lasing operation. Origin of this noise is a superposition of many generation-recombination processes through defects formed centers with widely distributed capture parameters. It was shown that cross-correlation between electrical and optical fluctuations indicates presence of defects at the active region interface that forms leakage current channels, accelerates LD degradation and cause negatively correlated optical and electrical fluctuations. Decomposition of noise spectral density and cross-correlation coefficient into independent noise components (noise sources) enables evaluation of correlated (that are located in the active region) and uncorrelated (that are in the passive layers of LD) optical and electrical noise sources. Investigated FP laser diodes are distinguished by mode-hopping effect and causes intensive highly correlated Lorentzian-type optical and electrical fluctuations. Origin of those fluctuations is generation–recombination processes through defects formed centers in the barrier layers. Thus, the correlated electrical and light intensity fluctuations are related with the random potential height fluctuations of barrier layer. Also it was shown that electrical characteristics (derivative of current-voltage characteristic, conductance and capacitance) can be used for the threshold current identification
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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