1,720,971 research outputs found
Analysis of DC Current Accelerated Life Tests of GaN LEDs Using a Weibull-Based Statistical Model
No full textGallium-nitride-based light-emitting diode (LED) accelerated
life tests were carried out over devices adopting two
different packaging schemes (i.e., with plastic transparent encapsulation
or with pure metallic package). Data analyses were
done using a Weibull-based statistical description with the aim
of estimating the effect of high current on device performance.
A consistent statistical model was found with the capability to
estimate the mean time to failure (MTTF) of devices during DC
current stress and the accelerating factors of high current stresses
Reliability of GaN-based LEDs
No full textWe report the results of a reliability evaluation plan carried out on GaN/InGaN
blue LEDs, including life tests at RT at three current levels: 20 mA, 50 mA, 100
mA, thermal storage at high ambient temperature (up to 300°C), and finally high
current density (≈100 A/cm2 ) and high junction temperature (300 °C). Failure
modes consist of: (a) an increase in series resistance and/or forward voltage; (b)
an increase in the tunneling component of forward diode current, and of reverse
current; (c) a substantial degradation of optical intensity. Device degradation is
correlated with a remarkable decrease in the apparent doping and with the
appearance of deep levels having activation energies of 0.55 ±0.05 eV and 1.21
eV, which may act as "dark" centers. Degradation has been interpreted as a result
of the instability of dopant in the p-layer. Breaking of Mg-H complexes, with
subsequent formation of Mg-H2 and Mg-H-N can in fact explain both the active
doping decrease (resulting in increased p-layer resistivity, higher forward voltage
and series resistance, and increasing current crowding), and the occurrence of
deep levels
Characterization of power LEDs for general lighting application
No full textA full characterization of commercial power LEDs for
general lighting application was performed in order to
identify the more proper bias condition. Continuous and
pulsed operating conditions were investigated taking into
account the initial device efficiency, in term of output
optical power over dissipated electrical power, and the
operating temperature. The aim of this work was to establish
the better compromise of bias condition with small
power waste and long devices operating life. The DC bias
shows better characteristics in term of devices initial efficiency,
but high operating temperature avoidable with a
good but usually expensive heat sink. High current pulsed
bias results in lower efficiency, but, also, lower average
operating temperature leading to longer lifetime
Accelerated aging of GaN light emitting diodes studied by 1/f and RTS noise
No full textBecause of their ultra brightness, GaN light emitting diodes (LEDs) becomes a promising light sources for
daily lighting. The growing market requires high reliability and long lifetime. Degradation mechanisms due to
accelerated ageing in GaN LED have previously been investigated by capacitance spectroscopy or light emission
mapping. In this paper low frequency noise (LFN) is used as a diagnostic tool to study degradation
mechanisms in GaN LEDs submitted to accelerated agein
Defect diagnostics of degradation mechanisms of GaN-based LEDs after accelerated DC current ageing
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Degradation mechanisms of GaN-based LEDs after accelerated DC current aging
No full textThis work presents the results of an extensive DC current aging and failure analysis carried out on blue InGaN/GaN LEDs which identify failure mechanisms related to package degradation, changes in effective doping profile, and generation of deep levels. DLTS and photocurrent spectra indicate the creation of extended defects in devices aged at very high current density
Factors limiting the High Brightness InGaN LEDs performance at high injection current bias
No full textVariations on the Author
Full text link“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
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