scholarly journals Identifying the cause of thermal droop in GaInN-based LEDs by carrier- and thermo-dynamics analysis

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Dong-Pyo Han ◽  
Gyeong Won Lee ◽  
Sangjin Min ◽  
Dong-Soo Shin ◽  
Jong-In Shim ◽  
...  
Keyword(s):  
Carrier Lifetime ◽  
Complex Dynamics ◽  
Physical Factor ◽  
Physical Factors ◽  
Temperature Dependent ◽  
Light Emitting ◽  
Carrier Lifetimes ◽  
Driving Current ◽  
Wide Range ◽  
Thermal Droop

Abstract This study aims to elucidate the carrier dynamics behind thermal droop in GaInN-based blue light-emitting diodes (LEDs) by separating multiple physical factors. To this end, first, we study the differential carrier lifetimes (DCLs) by measuring the impedance of a sample LED under given driving-current conditions over a very wide operating temperature range of 300 K–500 K. The measured DCLs are decoupled into radiative carrier lifetime (τR) and nonradiative carrier lifetime (τNR), via utilization of the experimental DCL data, and then very carefully investigated as a function of driving current over a wide range of operating temperatures. Next, to understand the measurement results of temperature-dependent τR and τNR characteristics, thermodynamic analysis is conducted, which enables to look deeply into the temperature-dependent behavior of the carriers. On the basis of the results, we reveal that thermal droop is originated by the complex dynamics of multiple closely interrelated physical factors instead of a single physical factor. In particular, we discuss the inherent cause of accelerated thermal droop with elevated temperature.

Some factors influencing landholder opinion of the native grass Microlaena stipoides

2004 ◽  
Vol 26 (2) ◽  
pp. 178 ◽  
Author(s):  
Catherine Allan ◽  
R. D. B. Whalley
Keyword(s):  
Physical Factor ◽  
Annual Rainfall ◽  
Physical Factors ◽  
Value Judgments ◽  
Actual Performance ◽  
Ecotypic Variation ◽  
Factors Influencing ◽  
Divergence Of Opinion ◽  
Wide Range ◽  
Microlaena Stipoides

Microlaena stipoides is widespread in the higher rainfall areas of Australia. It is consistently reported in the literature as providing high quality forage, yet anecdotal evidence suggests a wide range of opinions about the value of M. stipoides among graziers who manage areas with abundant M. stipoides. This paper addresses three questions relating to this divergence of opinion. Are landholders responding to inherent variability within M. stipoides? Is M. stipoides responding to different site and management conditions, prompting landholders to value it preferentially where site or management suit? Or are the landholders' judgments of M. stipoides influenced less by the actual performance of the grass on their properties than by social factors? Data collected from ten properties in the Victorian Upper Murray included a morphological assessment of M. stipoides samples, quantitative site and pasture information and qualitative data from interviews with property managers. Ecotypic variation and responses to site and management variables were found, but there were no apparent relationships between these parameters and the value judgments made by the landholders. The only physical factor which appeared to have any influence on landholder opinion was the annual rainfall for their property, although this was not through direct impact on other site attributes. It seems that social rather than physical factors may need to be explored in order to understand the factors influencing landholder opinion of M. stipoides.

Multifunctional luminescence properties of co-doped lanthanide metal organic frameworks

2015 ◽  
Vol 44 (20) ◽  
pp. 9588-9595 ◽  
Author(s):  
Shanghua Xing ◽  
Guang Zeng ◽  
Xiaomin Liu ◽  
Fen Yang ◽  
Zhiqiang Hao ◽  
...  
Keyword(s):  
Metal Organic Frameworks ◽  
Luminescent Materials ◽  
Temperature Dependent ◽  
Light Emitting ◽  
Co Doping ◽  
Wide Range ◽  
Metal Organic ◽  
Lanthanide Metal ◽  
Co Doped ◽  
Luminescence Behavior

Multifunctional luminescent materials of six Ln-MOFs have been designed and synthesized by the co-doping strategy. Thus a wide range of light emitting spectra and different temperature-dependent luminescence behavior were displayed.

Temperature-dependent minority-carrier lifetime measurements of red AlGaAs light emitting diodes

1995 ◽  
Vol 24 (10) ◽  
pp. 1407-1412 ◽  
Author(s):  
F. M. Steranka ◽  
D. C. Defevere ◽  
Camras ◽  
S. L. Rudaz ◽  
D. K. Mc Elfresh ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Carrier Lifetime ◽  
Minority Carrier ◽  
Minority Carrier Lifetime ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Light Emitting

scholarly journals Physiologically based control of the process of gentle light awakening

2021 ◽  
Vol 2127 (1) ◽  
pp. 012064
Author(s):  
A B Fedortsov ◽  
M O Silivanov
Keyword(s):  
Computer Control ◽  
Visible Spectrum ◽  
Well Being ◽  
Physical Factor ◽  
Short Wave ◽  
Physical Factors ◽  
Light Emitting ◽  
Rods And Cones ◽  
The Awakening ◽  
Human Eyes

Abstract The well-being of a person and the efficiency of his production activities are largely determined by the correspondence of the biorhythms of a person to his working schedule. As it was established at the molecular and genetic level, the main physical factor that allows us to control human biorhythms is light (Nobel Prize 2017). Modern studies of ophthalmologists have found a third type of photoreceptors in human eyes, in addition to rods and cones. These receptors are not intended for receiving images, but primarily for correcting biorhythms, including controlling the process of awakening. The third type of receptors are sensitive mainly in the short-wave, blue region of the visible spectrum. In recent years light-emitting diodes have appeared. However, these devices do not take into account the current requirements for the spectrum of the awakening radiation, and even more so do not allow it to be adjusted during the awakening process according to the necessary program. We offer a technology for gentle awakening of the employee, based on modern concepts of ophthalmology and biorhythmology. The technology uses computer control of the physical factors of awakening-light and sound.

Reduction of carbon impurities in aluminium nitride from time-resolved chemical vapour deposition using trimethylaluminum

2020 ◽  
Author(s):  
Polla Rouf ◽  
Pitsiri Sukkaew ◽  
Lars Ojamäe ◽  
Henrik Pedersen
Keyword(s):  
Chemical Vapour Deposition ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Aluminium Nitride ◽  
Methyl Groups ◽  
Time Resolved ◽  
Thermally Induced ◽  
Light Emitting ◽  
Carbon Impurities ◽  
Wide Range

<p>Aluminium nitride (AlN) is a semiconductor with a wide range of applications from light emitting diodes to high frequency transistors. Electronic grade AlN is routinely deposited at 1000 °C by chemical vapour deposition (CVD) using trimethylaluminium (TMA) and NH<sub>3</sub> while low temperature CVD routes to high quality AlN are scarce and suffer from high levels of carbon impurities in the film. We report on an ALD-like CVD approach with time-resolved precursor supply where thermally induced desorption of methyl groups from the AlN surface is enhanced by the addition of an extra pulse, H<sub>2</sub>, N<sub>2</sub> or Ar between the TMA and NH<sub>3</sub> pulses. The enhanced desorption allowed deposition of AlN films with carbon content of 1 at. % at 480 °C. Kinetic- and quantum chemical modelling suggest that the extra pulse between TMA and NH<sub>3</sub> prevents re-adsorption of desorbing methyl groups terminating the AlN surface after the TMA pulse. </p>

scholarly journals Study and Assessment of Defect and Trap Effects on the Current Capabilities of a 4H-SiC-Based Power MOSFET

Electronics ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 735
Author(s):  
Fortunato Pezzimenti ◽  
Hichem Bencherif ◽  
Giuseppe De Martino ◽  
Lakhdar Dehimi ◽  
Riccardo Carotenuto ◽  
...  
Keyword(s):  
Drain Current ◽  
Oxide Semiconductor ◽  
Temperature Dependent ◽  
Channel Mobility ◽  
Blocking Voltage ◽  
Current Voltage ◽  
Wide Range ◽  
Temperature Ranges ◽  
Joint Contribution ◽  
State Resistance

A numerical simulation study accounting for trap and defect effects on the current-voltage characteristics of a 4H-SiC-based power metal-oxide-semiconductor field effect transistor (MOSFET) is performed in a wide range of temperatures and bias conditions. In particular, the most penalizing native defects in the starting substrate (i.e., EH6/7 and Z1/2) as well as the fixed oxide trap concentration and the density of states (DoS) at the 4H-SiC/SiO2 interface are carefully taken into account. The temperature-dependent physics of the interface traps are considered in detail. Scattering phenomena related to the joint contribution of defects and traps shift the MOSFET threshold voltage, reduce the channel mobility, and penalize the device current capabilities. However, while the MOSFET on-state resistance (RON) tends to increase with scattering centers, the sensitivity of the drain current to the temperature decreases especially when the device is operating at a high gate voltage (VGS). Assuming the temperature ranges from 300 K to 573 K, RON is about 2.5 MΩ·µm2 for VGS > 16 V with a percentage variation ΔRON lower than 20%. The device is rated to perform a blocking voltage of 650 V.

scholarly journals LED Rail Signals: Full Hardware Realization of Apparatus with Independent Intensity by Temperature Changes

Electronics ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1291
Author(s):  
Giuseppe Schirripa Schirripa Spagnolo ◽  
Fabio Leccese
Keyword(s):  
Temperature Sensor ◽  
Energy Efficient ◽  
Light Emitting Diode ◽  
Junction Temperature ◽  
Light Emitting ◽  
Temperature Changes ◽  
Wide Range ◽  
International Regulations ◽  
Long Lifetime ◽  
Set Up

Nowadays, signal lights are made using light-emitting diode arrays (LEDs). These devices are extremely energy efficient and have a very long lifetime. Unfortunately, especially for yellow/amber LEDs, the intensity of the light is closely related to the junction temperature. This makes it difficult to design signal lights to be used in naval, road, railway, and aeronautical sectors, capable of fully respecting national and international regulations. Furthermore, the limitations prescribed by the standards must be respected in a wide range of temperature variations. In other words, in the signaling apparatuses, a system that varies the light intensity emitted according to the operating temperature is useful/necessary. In this paper, we propose a simple and effective solution. In order to adjust the intensity of the light emitted by the LEDs, we use an LED identical to those used to emit light as a temperature sensor. The proposed system was created and tested in the laboratory. As the same device as the ones to be controlled is used as the temperature sensor, the system is very stable and easy to set up.

scholarly journals Solution-Processed OLEDs Based on Thermally Activated Delayed Fluorescence Copper(I) Complexes with Intraligand Charge-Transfer Excited State

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 1125
Author(s):  
Teng Teng ◽  
Jinfan Xiong ◽  
Gang Cheng ◽  
Changjiang Zhou ◽  
Xialei Lv ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Density Functional ◽  
Delayed Fluorescence ◽  
Quantum Yields ◽  
Functional Theory ◽  
Solution Processed ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Wide Range

A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3–24.1 μs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.

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