scholarly journals Origin of thermal quenching of exciton photoluminescence in AlGaN epilayers

2021 ◽  
Vol 61 (2) ◽  
Author(s):  
O. Kravcov ◽  
J. Mickevičius ◽  
G. Tamulaitis
Keyword(s):  
Kinetic Monte Carlo ◽  
Stokes Shift ◽  
Thermal Quenching ◽  
Localized States ◽  
Monte Carlo Algorithm ◽  
Nonradiative Recombination ◽  
Al Content ◽  
Temperature Dependences ◽  
High Al Content ◽  
Exciton System

Dynamics of a low-density exciton system is simulated using the kinetic Monte Carlo algorithm. The temperature dependences of photoluminescence (PL) intensity and PL band Stokes shift in a high-Al-content AlGaN epi­layer are calculated and fitted to the experimentally measured ones. The key features of nonradiative recombination via delocalized states and direct tunnelling to nonradiative recombination centres and their influence on PL efficiency are analysed. A strong influence of the tunnelling-based recombination in AlGaN epilayers with a large ratio between the densities of nonradiative recombination centres and localized states is revealed.

Low-Temperature Operation of Green, Blue and UV InGaN/GaN Multiple-Quantum-Well Light-Emitting Diodes

2003 ◽  
Vol 764 ◽  
Author(s):  
X. A. Cao ◽  
S. F. LeBoeuf ◽  
J. L. Garrett ◽  
A. Ebong ◽  
L. B. Rowland ◽  
...  
Keyword(s):  
Quantum Well ◽  
Light Emitting Diodes ◽  
Multiple Quantum Well ◽  
Light Output ◽  
Localized States ◽  
Multiple Quantum ◽  
Nonradiative Recombination ◽  
Light Emitting ◽  
Temperature Range ◽  
Green Leds

Absract:Temperature-dependent electroluminescence (EL) of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission energies ranging from 2.3 eV (green) to 3.3 eV (UV) has been studied over a wide temperature range (5-300 K). As the temperature is decreased from 300 K to 150 K, the EL intensity increases in all devices due to reduced nonradiative recombination and improved carrier confinement. However, LED operation at lower temperatures (150-5 K) is a strong function of In ratio in the active layer. For the green LEDs, emission intensity increases monotonically in the whole temperature range, while for the blue and UV LEDs, a remarkable decrease of the light output was observed, accompanied by a large redshift of the peak energy. The discrepancy can be attributed to various amounts of localization states caused by In composition fluctuation in the QW active regions. Based on a rate equation analysis, we find that the densities of the localized states in the green LEDs are more than two orders of magnitude higher than that in the UV LED. The large number of localized states in the green LEDs are crucial to maintain high-efficiency carrier capture at low temperatures.

Nanocrystalline Phosphors for Lighting and Detection Applications

2010 ◽  
Vol 654-656 ◽  
pp. 1130-1133 ◽  
Author(s):  
Christopher J. Summers ◽  
Hisham M. Menkara ◽  
Richard A. Gilstrap ◽  
Mazen Menkara ◽  
Thomas Morris
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Shell Growth ◽  
Stokes Shift ◽  
Thermal Quenching ◽  
High Sensitivity ◽  
In Situ Monitoring ◽  
White Leds ◽  
Sensing Applications ◽  
Improved Stability

We report the development of new nanoparticle phosphors and quantum dot structures designed for applications to enhance the color rendering and efficiency of high brightness white LEDs, as well as for bio-sensing applications. The intrinsic problem of self-absorption, high toxicity, and high sensitivity to thermal quenching of conventional quantum dot systems has prevented their adoption to LED devices. Doped Cd-free quantum dots may circumvent these issues due to their distinct Stokes shift and improved stability at high temperature. We report on the modification of Mn-doped ZnSe/ZnS core-shell quantum dots for application to the (blue diode + yellow emitter) white LED system. Band gap tuning for 460 nm excitation, inorganic shell growth and in-situ monitoring for enhanced efficiency, and analysis of thermal stability will are reported.

Temperature behavior of X-Ray luminescence spectra of ZnSe

2022 ◽  
Author(s):  
I. Abbasov ◽  
M. Musayev ◽  
D. Askerov ◽  
J. Huseynov ◽  
E. Gavrishuk ◽  
...  
Keyword(s):  
Thermal Quenching ◽  
Chemical Vapor ◽  
Temperature Behavior ◽  
Luminescence Spectra ◽  
Uv Laser ◽  
Green Band ◽  
Spectra Analysis ◽  
X Ray ◽  
Temperature Dependences ◽  
The Given

In the given paper, the temperature dependences ([Formula: see text]–300 K) of the green band intensity at wavelengths [Formula: see text] nm and [Formula: see text] nm have been measured and observed, respectively, from the polished and unpolished surface (PS and unPS) of a polycrystalline CVD (chemical vapor deposition) ZnSe sample upon excitation by X-ray quanta ([Formula: see text]. In both cases, the activation energy of thermal quenching has been determined, and the reasons for thermal quenching have been considered in detail. Along with XRL spectra analysis, the temperature behavior of the green band observed upon excitation by an ultraviolet (UV) laser (He–Cd, [Formula: see text] nm) from the PS and unPS in the temperature range [Formula: see text]–200 K has been discussed in more detail.

Dielectric properties of anodized Al-Ta alloy films with high Al content

1975 ◽  
Vol 27 (1) ◽  
pp. 111-121 ◽  
Author(s):  
A. Schauer ◽  
M. Roschy ◽  
W. Juergens
Keyword(s):  
Dielectric Properties ◽  
Alloy Films ◽  
Al Content ◽  
High Al Content

scholarly journals Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films

2000 ◽  
Vol 5 (S1) ◽  
pp. 796-802 ◽  
Author(s):  
Yong-Hoon Cho ◽  
G. H. Gainer ◽  
J. B. Lam ◽  
J. J. Song ◽  
W Yang ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Stokes Shift ◽  
Energy Shift ◽  
Peak Position ◽  
Time Resolved ◽  
Temperature Range ◽  
Al Content ◽  
Peak Energy ◽  
Emission Behavior ◽  
Pl Intensity

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.

scholarly journals Lake sedimentary biogenic silica from diatoms constitutes a significant global sink for aluminium

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Dong Liu ◽  
Peng Yuan ◽  
Qian Tian ◽  
Hongchang Liu ◽  
Liangliang Deng ◽  
...  
Keyword(s):  
Biogenic Silica ◽  
Biogeochemical Cycle ◽  
Biochemical Processes ◽  
Al Content ◽  
High Al Content ◽  
Global Oceans

Abstract Diatoms play an important role in marine biogeochemical cycle of aluminum (Al), as dissolved Al is taken up by diatoms to build their siliceous frustules and is involved in the sedimentation of diatomaceous biogenic silica (BSi). The Al incorporation in BSi facilitates decreasing the dissolution of marine BSi and thus substantially influences the biochemical processes driven by diatoms, such as CO2 sequestration. However, the role of lake BSi in the terrestrial biochemical Al cycle has not been explored, though lakes represent the second-largest sink for BSi. By identifying the previously unexplored high Al/Si atomic ratios (up to 0.052) in lake BSi, here we show lake BSi is a large terrestrial Al pool due to its high Al content, and lake sedimentary BSi constitutes a significant global sink for Al, which is on the same magnitude as the Al sink in global oceans.

Theory of Defects, Doping, Surfaces and Interfaces in Wide Gap Nitrides

1996 ◽  
Vol 423 ◽  
Author(s):  
J. Bernholc ◽  
P. Boguslawski ◽  
E. L. Briggs ◽  
M. Buongiorno Nardelli ◽  
B. Chen ◽  
...  
Keyword(s):  
Nearest Neighbor ◽  
Group Iv ◽  
Type I ◽  
Shallow Acceptor ◽  
Surface And Interface ◽  
Al Content ◽  
Surfaces And Interfaces ◽  
High Concentrations ◽  
P Type ◽  
High Al Content

AbstractThe results of extensive theoretical studies of group IV impurities and surface and interface properties of nitrides are presented and compared with available experimental data. Among the impurities, we have considered substitutional C, Si, and Ge. CN is a very shallow acceptor, and thus a promising p-type dopant. Both Si and Ge are excellent donors in GaN. However, in AlGaN alloys the DX configurations are stable for a sufficiently high Al content, which quenches the doping efficiency. At high concentrations, it is energetically favorable for group IV impurities to form nearest-neighbor Xcation-XN pairs. Turning to surfaces, AIN is known to exhibit NEA. We find that the NEA property depends sensitively on surface reconstruction and termination. At interfaces, the strain effects on the band offsets range from 20% to 40%, depending on the substrate. The AIN/GaN/InN interfaces are all of type I, while the A10.5Ga0.5 N/A1N zinc-blende (001) interface may be of type II. Further, the calculated bulk polarizations in wurtzite AIN and GaN are -1.2 and -0.45 μC/cm2, respectively, and the interface contribution to the polarization in the GaN/AlN wurtzite multi-quantum-well is small.

Preparation of discrete colloidal ZSM-5 crystals with high Al-content

2010 ◽  
Vol 18 (6) ◽  
pp. 723-728 ◽  
Author(s):  
Börje Gevert ◽  
Lars Eriksson ◽  
Anders Törncrona
Keyword(s):  
Al Content ◽  
High Al Content

THE EFFECTS OF INCREASING AlN MOLE FRACTION ON THE PERFORMANCE OF AlGaN ACTIVE REGIONS CONTAINING NANOMETER SCALE COMPOSITIONALLY INHOMOGENEITIES

2009 ◽  
Vol 19 (01) ◽  
pp. 69-76
Author(s):  
A.V. SAMPATH ◽  
M.L REED ◽  
C. MOE ◽  
G.A. GARRETT ◽  
E.D. READINGER ◽  
...  
Keyword(s):  
Mole Fraction ◽  
Point Defects ◽  
Flip Chip ◽  
Radiative Lifetime ◽  
Active Regions ◽  
Nanometer Scale ◽  
Nonradiative Recombination ◽  
Photoluminescence Intensity ◽  
Al Content ◽  
Order Of Magnitude

In this paper we report on the characterization of n - Al 0.51 Ga 0.49 N active regions and the fabrication of ultraviolet LEDs that contain self-assembled, nanometer-scale compositional inhomogeneities ( NCI - AlGaN ) with emission at ~290 nm. These active regions exhibit reduced integrated photoluminescence intensity and PL lifetime relative to 320 nm NCI - AlGaN active regions that have significantly lower AlN mole fraction, despite having more than an order of magnitude fewer threading dislocations, as measured by transmission electron microscopy. This behavior is attributed to nonradiative recombination associated with the presence of a larger density of point defects in the higher Al content samples. The point defects are ameliorated somewhat by the lower density of NCI AlGaN regions in the higher Al content samples, which leads to a larger concentration of carriers in the NCI and concomitant reduced radiative lifetime that may account for the high observed peak IQE (~ 25%). Prototype flip chip double heterostructure-NCI- ultraviolet light emitting diodes operating at 292 nm have been fabricated that employ a 50% NCI - AlGaN active region.

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