Abstract
Immiscible semiconductors are of premier importance since the source of lighting has been replaced by white light-emitting-diodes (LEDs) composed of thermodynamically immiscible In
x
Ga
1−
x
...N blue LEDs and yellow phosphors. For realizing versatile deep-ultraviolet to near-infrared light-emitters, Al
1−
x
In
x
N alloys are one of the desirable candidates. Here we exemplify the appearance and self-formation sequence of compositional superlattices in compressively strained
m
-plane Al
1−
x
In
x
N films. On each terrace of atomically-flat
m
-plane GaN, In- and Al-species diffuse toward a monolayer (ML) step edge, and the first and second uppermost <
$$\stackrel{-}{1}\stackrel{-}{1}20$$
1
-
1
-
20
> cation-rows are preferentially occupied by Al and In atoms, respectively, because the configuration of one In-N and two Al-N bonds is more stable than that of one Al-N and two In-N bonds. Subsequent coverage by next <
$$\stackrel{-}{1}\stackrel{-}{1}20$$
1
-
1
-
20
> Al-row buries the <
$$\stackrel{-}{1}\stackrel{-}{1}20$$
1
-
1
-
20
> In-row, producing nearly Al
0.5
In
0.5
N cation-stripe ordering along 0001-axis on GaN. At the second Al
0.72
In
0.28
N layer, this ordinality suddenly lessens but In-rich and In-poor <
$$\stackrel{-}{1}\stackrel{-}{1}20$$
1
-
1
-
20
>-rows are alternately formed, which grow into respective {0001}-planes. Simultaneously, approximately 5-nm-period Al
0.70
In
0.30
N/Al
0.74
In
0.26
N ordering is formed to mitigate the lattice mismatch along 0001, which grow into approximately 5-nm-period Al
0.70
In
0.30
N/Al
0.74
In
0.26
N {
$$10\stackrel{-}{1}2$$
10
1
-
2
} superlattices as step-flow growth progresses. Spatially resolved cathodoluminescence spectra identify the emissions from particular structures.
The internal quantum efficiency (IQE) and photoluminescence lifetime τ PL of the near-band-edge emission in a ZnO single crystal grown by the hydrothermal method were measured by the omnidirectional ...photoluminescence and time-resolved photoluminescence spectroscopy, respectively. The IQE showed a monotonic increase when the cw photo pumping density exceeds 2.0 × 10 − 2 W cm−2, while a constant IQE was observed below that. By using the data set of IQE and τ PL measured under pulsed excitation conditions, radiative and nonradiative recombination lifetimes were separately quantified. Since a significant increase was observed for the nonradiative recombination lifetime, the origin of the IQE increase was revealed to be dominated by the saturation of nonradiative recombination centers.
Abstract
A process for activating Mg and its relationship with vacancy-type defects in Mg-implanted GaN were studied by positron annihilation spectroscopy. Mg
+
ions were implanted with an energy of ...10 keV, and the Mg concentration in the subsurface region (≤ 50 nm) was on the order of 10
19
cm
−3
. After the Mg-implantation, N
+
ions were implanted to provide a 300-nm-deep box profile with a N concentration of 6 × 10
18
cm
−3
. From capacitance–voltage measurements, the sequential implantation of N was found to enhance the activation of Mg. For N-implanted GaN before annealing, the major defect species were determined to Ga-vacancy related defects such as divacancy. After annealing below 1000 °C, the clustering of vacancies was observed. Above 1200 °C annealing, however, the size of the vacancies started to decrease, which was due to recombinations of vacancy clusters and excess N atoms in the damaged region. The suppression of vacancy clustering by sequential N-implantation in Mg-implanted GaN was attributed to the origin of the enhancement of the Mg activation.
Planar vacuum‐fluorescent‐display devices emitting polarized UV‐C, blue, and green light are demonstrated using immiscible Al1−xInxN nanostructures grown in nonpolar m‐directions. Despite the ...presence of high concentration of nonradiative recombination centers, the Al1−xInxN nanostructures emit polarized light with the luminescence lifetimes of 22–32 ps at 300 K. This defect‐resistant radiative performance suggests supernormal localized characteristics of electron–hole pairs.
Substantial investments into laboratories, notably sophisticated equipment, have been made over time to detect emerging diseases close to their source. Diagnostic capacity has expanded as a result, ...but challenges have emerged. The Equipment Management and Sustainability Survey was sent to the Veterinary Services of 182 countries in mid-2019. We measured the status of forty types of laboratory equipment used in veterinary diagnostic laboratories. Of the 68,455 items reported from 227 laboratories in 136 countries, 22% (14,894/68,455) were improperly maintained, and 46% (29,957/65,490) were improperly calibrated. Notable differences were observed across World Bank income levels and regions, raising concerns about equipment reliability and the results they produce. Our results will advise partners and donors on how best to support low-resource veterinary laboratories to improve sustainability and fulfill their mandate toward pandemic prevention and preparedness, as well as encourage equipment manufacturers to spur innovation and develop more sustainable products that meet end-users’ needs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Internal quantum efficiency of radiation (IQE) for the near-band-edge (NBE) emission of freestanding-GaN crystals was observed by omnidirectional photoluminescence spectroscopy at various ...temperatures between 12 K and 300 K. A photoluminescence quenching ratio (Rq), defined by a spectrally integrated NBE emission obtained at 300 K to that obtained at 12 K, showed a lower value (2%) comparing with the IQE value (5.5%) for the GaN with the free electron concentration of 1 × 1017 cm−3 under cw photo-pumping density of 13 W cm−2. This difference arises from the nonlinear relationship between IQE and the external quantum efficiency owing to the photon recycling effect.
The relationship between the concentration of carbon (C) impurity, C, and quantum efficiency (QE) of radiation in n-type GaN crystals was clarified under photo-excitation conditions at room ...temperature. Since C acts as a trap for minority holes as well as a compensator for majority electrons, the external QE (EQE) and internal QE (IQE) values for the near-band-edge (NBE) emission showed a monotonic increase with decreasing C, where NBE EQE (IQE) values are 0.02% (0.70%) and 0.53% (14.2%) for C = 2.0 × 1016 cm−3 and C = 4.0 × 1014 cm−3, respectively, under a cw photo-pumping density of 140 W cm−2.
New WHO guidance could expand access to lab facilities
Laboratory biosafety is fundamental to controlling exposure to pathogens, protecting the laboratory workforce and the wider community against ...inadvertent exposures or releases. Since 1983, the World Health Organization (WHO)
Laboratory Biosafety Manual
(
LBM
) has encouraged countries to implement basic concepts in biological safety and to develop national codes of practice for the safe handling of pathogenic microorganisms in laboratories. But as technologies continue to evolve, and with them potential threats and benefits to laboratory safety, so too must approaches to biosafety. With revision toward the fourth edition of the
LBM
under way, we propose a shift in focus to a risk-based, technology-neutral, and cost-effective approach to biosafety, making sure that laboratory facilities, safety equipment, and work practices are locally relevant, proportionate, and sustainable. This will allow more flexibility in laboratory design, reduce focus on pathogen risk groups and biosafety levels as the de facto starting point of laboratory considerations, and place more emphasis on human factors and worker training. Improved sustainability of laboratory operations through lower construction and operating costs, particularly in resource-limited settings, may pave the way for equitable access to clinical and public health laboratory tests and biomedical research opportunities, without compromising safety.
Vacancy‐type defects in Mg‐implanted GaN are probed using monoenergetic positron beams. Mg+ ions are implanted to provide a 500‐nm‐deep box profile with Mg concentrations, Mg, of 1 × 1017–1 × 1019 ...cm−3 at room temperature. In the as‐implanted samples, the major defect species is a complex of a Ga vacancy (VGa) and a nitrogen vacancy (VN). After annealing above 1000 °C, the major defect species is changed to vacancy clusters due to vacancy agglomeration. This agglomeration is suppressed, and the agglomeration onset temperature is decreased with a decreasing Mg. For samples with Mg ≥ 1 × 1018 cm−3, the trapping rate of positrons by vacancy‐type defects decrease after annealing above 1100–1200 °C. This decreases is attributed to the change in the defect charge states from neutral to positive due to a downward shift of the Fermi level. The carrier trapping/detrapping properties of the vacancy‐type defects and their time dependences are also revealed.
Vacancy‐type defects in Mg‐implanted GaN are probed by means of positron annihilation. In the as‐implanted samples, the major defect species is identified as a complex of a Ga vacancy and a nitrogen vacancy. After annealing treatments, the defect species is changed to vacancy clusters due to vacancy agglomeration. Using positron annihilation and illumination technique, the carrier trapping/detrapping properties of the vacancy‐type defects are revealed.
PDF
