Highly efficient multiple-layer CdS quantum dot sensitized III-V solar cells.

In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found.

Improvement Performance of p-GaN Gate High-Electron-Mobility Transistors with GaN/AlN/AlGaN Barrier Structure.

This study demonstrates a particular composited barrier structure of high-electron-mobility transistors (HEMTs) with an enhancement mode composed of p-GaN/GaN/AlN/AlGaN/GaN. The purpose of the composite barrier structure device is to increase the maximum drain current, reduce gate leakage, and achieve lower on-resistance (Ron) performance. A comparison was made between the conventional device without the composited barrier and the device with the composited barrier structure. The maximum drain current is significantly increased by 37%, and Ron is significantly reduced by 23%, highlighting the synergistic impact of the composite barrier structure on device performance improvement. This reason can be attributed to the undoped GaN (u-GaN) barrier layer beneath p-GaN, which was introduced to mitigate Mg diffusion in the capping layer, thus addressing its negative effects. Furthermore, the AlN barrier layer exhibits enhanced electrical properties, which can be attributed to the critical role of high-energy-gap properties that increase the 2DEG carrier density and block leakage pathways. These traps impact the device behavior mechanism, and the simulation for a more in-depth analysis of how the composited barrier structure brings improvement is introduced using Synopsys Sentaurus TCAD.

High thermal stability of correlated color temperature using current compensation in hybrid warm white high-voltage LEDs.

This study experimentally and numerically examines the correlated color temperature (CCT) stability issue for hybrid warm white high-voltage light-emitting diodes (HV-LEDs) by using a current compensation method. This method could efficiently maintain the CCT stability factor at approximately 1.0 and yield greater color uniformity with Δu'v' values ranging from 0.017 to 0.003 in CIE 1976 chromaticity coordinates. The simulation results show that the red chip intensity drop is the primary cause of CCT instability in the hybrid warm white system when the temperature increases. Therefore, Furthermore, results indicate that the relative lumen drop improves from 21% to 15% by using a current compensation method.

An obesity paradox of Asian body mass index after cardiac surgery: arterial oxygenations in duration of mechanic ventilation.

BACKGROUND: Numerous studies have documented an obesity paradox that overweight of Caucasian patients has better prognosis after cardiac surgery. This study is to examine Asian patients' BMI to see whether an obesity paradox exists in DMV after cardiac surgery. METHODS: A retrospective study consisted of 428 patients after cardiac surgery from January 2006 to December 2010 in the medical center of Taiwan. The Asian BMI was divided into 3 groups: under-normal weight patients (BMI < 24; n = 165), overweight patients (BMI 24 to <27; n = 130), and obese patients (BMI ≥ 27; n = 133). Multivariable analysis and paired t were used to compare all variables. RESULTS: Overweight patients were significantly associated with the shortest DMV. Under-normal weight patients had significantly better oxygenations of AaDO2 and P/F ratio in the DMV; however, they correlated with the longest DMV, older age, more female, lower LVSV, higher BUN, more dialysis-dependent, and poorer outcomes, namely, 1-year mortality, HAP, reintubation, tracheotomy, and LOS. CONCLUSIONS: Asian overweight patients after cardiac surgery have better prognosis. Under-normal weight patients have higher risk factors, longer DMV, and poorer outcomes; even though they have better arterial oxygenations, they seem to need better arterial oxygenations for successful weaning ventilator.

A Brief Overview of the Rapid Progress and Proposed Improvements in Gallium Nitride Epitaxy and Process for Third-Generation Semiconductors with Wide Bandgap.

In this paper, we will discuss the rapid progress of third-generation semiconductors with wide bandgap, with a special focus on the gallium nitride (GaN) on silicon (Si). This architecture has high mass-production potential due to its low cost, larger size, and compatibility with CMOS-fab processes. As a result, several improvements have been proposed in terms of epitaxy structure and high electron mobility transistor (HEMT) process, particularly in the enhancement mode (E-mode). IMEC has made significant strides using a 200 mm 8-inch Qromis Substrate Technology (QST®) substrate for breakdown voltage to achieve 650 V in 2020, which was further improved to 1200 V by superlattice and carbon-doped in 2022. In 2016, IMEC adopted VEECO metal-organic chemical vapor deposition (MOCVD) for GaN on Si HEMT epitaxy structure and the process by implementing a three-layer field plate to improve dynamic on-resistance (RON). In 2019, Panasonic HD-GITs plus field version was utilized to effectively improve dynamic RON. Both reliability and dynamic RON have been enhanced by these improvements.

Improving Performance and Breakdown Voltage in Normally-Off GaN Recessed Gate MIS-HEMTs Using Atomic Layer Etching and Gate Field Plate for High-Power Device Applications.

A typical method for normally-off operation, the metal-insulator-semiconductor-high electron mobility transistor (MIS-HEMT) has been investigated. Among various approaches, gate recessed MIS-HEMT have demonstrated a high gate voltage sweep and low leakage current characteristics. Despite their high performance, obtaining low-damage techniques in gate recess processing has so far proven too challenging. In this letter, we demonstrate a high current density and high breakdown down voltage of a MIS-HEMT with a recessed gate by the low damage gate recessed etching of atomic layer etching (ALE) technology. After the remaining 3.7 nm of the AlGaN recessed gate was formed, the surface roughness (Ra of 0.40 nm) was almost the same as the surface without ALE (no etching) as measured by atomic force microscopy (AFM). Furthermore, the devices demonstrate state-of-the-art characteristics with a competitive maximum drain current of 608 mA/mm at a VG of 6 V and a threshold voltage of +2.0 V. The devices also show an on/off current ratio of 109 and an off-state hard breakdown voltage of 1190 V. The low damage of ALE technology was introduced into the MIS-HEMT with the recessed gate, which effectively reduced trapping states at the interface to obtain the low on-resistance (Ron) of 6.8 Ω·mm and high breakdown voltage performance.

Highly efficient CdS-quantum-dot-sensitized GaAs solar cells.

We demonstrate a hybrid design of traditional GaAs-based solar cell combined with colloidal CdS quantum dots. With anti-reflective feature at long wavelength and down-conversion at UV regime, the CdS quantum dot effectively enhance the overall power conversion efficiency by as high as 18.9% compared to traditional GaAs-based device. A more detailed study showed an increase of surface photoconductivity due to UV presence, and the fill factor of the solar cell can be improved accordingly.

Improvement in uniformity of emission by ZrO2 nano-particles for white LEDs.

The high luminous efficiency and superior uniformity of angular-dependent correlated color temperature (CCT) white light-emitting diodes have been investigated by ZrO2 nano-particles in a remote phosphor structure. By adding ZrO2 nano-particles with silicone onto the surface of the phosphor layer, the capability of light scattering could be enhanced. In particular, the intensity of blue light at large angles was increased and the CCT deviations could be reduced. Besides, the luminous flux was improved due to the ZrO2 nano-particles with silicone providing a suitable refractive index between air and phosphor layers. This novel structure reduces angular-dependent CCT deviations from 1000 to 420 K in the range of -70° to 70°. Moreover, the enhancement of lumen flux was increased by 2.25% at a driving current 120 mA, compared to a conventional remote phosphor structure without ZrO2 nano-particles. Consequently, the ZrO2 nano-particles in a remote phosphor structure could not only improve the uniformity of lighting but also increase the light output.

Enhanced conversion efficiency of a crystalline silicon solar cell with frustum nanorod arrays.

Enhanced photoelectric conversion is demonstrated in a crystalline silicon (c-Si) solar cell with frustum nanorod arrays (FNAs), fabricated using colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the cell with FNAs improves the power conversion efficiency by nearly 30%, compared to a conventional wet-chemical-textured reference. The enhancement mostly arises from the superior antireflective properties for wavelengths between 400 nm and 1000 nm. In that spectral range, we show that photons gained by reflection reduction directly contribute to collected carriers without auxiliary losses due to nano-fabrication. Moreover, the omnidirectional antireflection of FNAs is also investigated using an angle-resolved reflectance spectroscopy. The dimensions of FNAs are further analyzed with numerical calculations based on Maxwell's equations. The optimized short-circuit current density achieves nearly 40 mA/cm2, corresponding to a 16% enhancement compared to the conventional device.

Patterned structure of remote phosphor for phosphor-converted white LEDs.

High efficiency white light-emitting diodes with superior color-mixing have been investigated. It is suggested that the patterned remote phosphor structure could improve the uniformity of angular-dependent correlated color temperature (CCT) and achieve high chromatic stability in wider operating current range, as compared to the conventional remote phosphor coating structure. In this experiment, we employed a pulse spray coating method to place the patterned phosphor on the package and to leave a window region. The window area, a clear space without coating of the phosphor not only increases the extraction efficiency of blue rays at large angle, but also improves the stability of angular-dependent CCT. Moreover, the CCT deviation could be reduced from 1320 K to 266 K by this patterned remote phosphor method, and the stray blue/yellow light within the package can be effectively reduced and controlled. The design was verified both experimentally and theoretically.

Enhanced efficiency for c-Si solar cell with nanopillar array via quantum dots layers.

The enhanced efficiency of the crystalline silicon (c-Si) solar cell with nanopillar arrays (NPAs) was demonstrated by deployment of CdS quantum dots (QDs). The NPAs was fabricated by the colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the device with CdS QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. For further investigation, the excitation spectrum of photoluminescence (PL), absorbance spectrum, current-voltage (I-V) characteristics, reflectance and external quantum efficiency of the device was measured and analyzed. It is noteworthy that the enhancement of efficiency could be attributed to the photon down-conversion, the antireflection, and the improved electrical property.

Efficiency enhancement InGaP/GaAs dual-junction solar cell with subwavelength antireflection nanorod arrays.

The enhanced conversion efficiency of the InGaP/GaAs dual-junction solar cell was demonstrated utilizing broad-band and omnidirectional antireflection nanorod arrays. The nanorod arrays were fabricated by self-assembled Ni clusters, followed by inductively-coupled-plasma reactive ion etching. The conversion efficiency measured under one-sun air mass 1.5 global illuminations at room temperature was improved by 10.8%. The light absorption efficiencies of the top InGaP and bottom GaAs cells were also studied under the influence of nanorod arrays. The enhanced absorption efficiency was mostly contributed from the short wavelength absorption by top cell. Surface nanorod arrays served not only as broad-band omnidirectional antireflection layers but also scattering sources. The structure can be further optimized to obtain the maximum conversion efficiency.

A highly efficient hybrid GaAs solar cell based on colloidal-quantum-dot-sensitization.

This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current.

White light emitting diodes with enhanced CCT uniformity and luminous flux using ZrO2 nanoparticles.

To enhance the uniformity of correlated color temperature (CCT) and luminous flux, we integrated ZrO2 nanoparticles into white light-emitting diodes. This novel packaging scheme led to a more than 12% increase in luminous flux as compared to that in conventional dispensing structures. This was attributed to the scattering effect of ZrO2 nanoparticles, which enhanced the utilization of blue light. Moreover, the CCT deviation was reduced from 522 to 7 K in a range of -70 to +70°, and essentially eliminated the yellow ring phenomenon. The haze measurement indicated strong scattering across the visible spectrum in the presence of ZrO2 in the silicone layer, and this finding also substantiates our claim. In addition, the chromaticity coordinate shift was steady in the ZrO2 dispensing package structure as the drive current increased, which is crucial for indoor lighting. Combined with its low cost, easy fabrication, and superior optical characteristics, ZrO2 nanoparticles can be an effective performance enhancer for the future generation of white light-emitting devices.

A novel randomly textured phosphor structure for highly efficient white light-emitting diodes.

We have successfully demonstrated the enhanced luminous flux and lumen efficiency in white light-emitting diodes by the randomly textured phosphor structure. The textured phosphor structure was fabricated by a simple imprinting technique, which does not need an expensive dry-etching machine or a complex patterned definition. The textured phosphor structure increases luminous flux by 5.4% and 2.5% at a driving current of 120 mA, compared with the flat phosphor and half-spherical lens structures, respectively. The increment was due to the scattering of textured surface and also the phosphor particles, leading to the enhancement of utilization efficiency of blue light. Furthermore, the textured phosphor structure has a larger view angle at the full width at half maximum (87°) than the reference LEDs.