Impacts of p-GaN layer thickness on the photoelectric and thermal performance of AlGaN-based deep-UV LEDs.

The effects of different p-GaN layer thickness on the photoelectric and thermal properties of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were investigated. The results revealed that appropriate thinning of the p-GaN layer enhances the photoelectric performance and thermal stability of DUV-LEDs, reducing current crowding effects that affect the external quantum efficiency and chip heat dissipation. The ABC + f(n) model was used to analyse the EQE, which helped in identifying the different physical mechanisms for DUV-LEDs with different p-GaN layer thickness. Moreover, the finite difference time domain simulation results revealed that the light-extraction efficiency of the DUV-LEDs exhibits a trend similar to that of damped vibration as the thickness of the p-GaN layer increases. The AlGaN-based DUV-LED with a p-GaN layer thickness of 20 nm exhibited the best photoelectric characteristics and thermal stability.

Sidewall geometric effect on the performance of AlGaN-based deep-ultraviolet light-emitting diodes.

In this study, deep-ultraviolet light-emitting diodes (DUV LEDs) with different chip sidewall geometries (CSGs) are investigated. The structure had two types of chip sidewall designs that combined DUV LEDs with the same p-GaN thickness. By comparing the differences of the characteristics such as the external quantum efficiency droops, light output power, light extraction efficiency (LEE), and junction temperature of these DUV LEDs, the self-heated effect and light-tracing simulation results have been clearly demonstrated to explain the inclined sidewalls that provide more possibility pathway for photons escape to increase the LEE of LEDs; thus, the DUV LEDs with the CSG presented improved performance. These results demonstrate the potential of CSG for DUV LED applications.

Study on the performance of high-voltage deep ultraviolet light-emitting diodes.

This study fabricated high-voltage, low-current DUV-LEDs by connecting two devices. Due to better current spreading and the enhanced reflective mirror effect, high-voltage devices present a higher dynamic resistance, emission output power, wall-plug efficiency, external quantum efficiency, and view angle than single traditional devices. The study found that when the injection current was 320 mA, the maximum output power was exhibited at 47.1 mW in the HV sample. The maximum WPE and EQE of high-voltage DUV-LEDs were 2.46% and 5.48%, respectively. Noteworthily, the redshift wavelength shifted from 287.5 to 280.5 nm, less than the traditional device-from 278 to 282 nm. Further, due to the uniform emission patterns in high-voltage devices, the view angle presents 130 degrees at 100 mA input current. In this study, the high-voltage device showed more excellent properties than the traditional device. In particular, it presented a high potential application in high-voltage circuits, which can remove transformers to eliminate extra power consumption.

Thermal behavior of AlGaN-based deep-UV LEDs.

This study utilized thin p-GaN, indium tin oxide (ITO), and a reflective passivation layer (RPL) to improve the performance of deep ultra-violet light-emitting diodes (DUV-LEDs). RPL reflectors, which comprise HfO2/SiO2 stacks of different thickness to maintain high reflectance, were deposited on the DUV-LEDs with 40 nm-thick p-GaN and 12 nm-thick ITO thin films. Although the thin p-GaN and ITO films affect the operation voltage of DUV-LEDs, the highly reflective RPL structure improved the WPE and light extraction efficiency (LEE) of the DUV-LEDs, yielding the best WPE and LEE of 2.59% and 7.57%, respectively. The junction temperature of DUV-LEDs with thick p-GaN increased linearly with the injection current, while that of DUV-LEDs with thin p-GaN, thin ITO, and RPL was lower than that of the Ref-LED under high injection currents (> 500 mA). This influenced the temperature sensitive coefficients (dV/dT, dLOP/dT, and dWLP/dT). The thermal behavior of DUV-LEDs with p-GaN and ITO layers of different thicknesses with/without the RPL was discussed in detail.

Enhanced external quantum efficiencies of AlGaN-based deep-UV LEDs using reflective passivation layer.

In this study, deep ultraviolet light-emitting diodes (DUV-LEDs) with a reflective passivation layer (RPL) were investigated. The RPL consists of HfO2/SiO2 stacks as distributed Bragg reflectors, which are deposited on two DUV-LEDs with different p-GaN thicknesses. The RPL structure improved the external quantum efficiency droops of the DUV-LEDs with thick and thin p-GaN, thereby increasing their light output power by 18.4% and 39.4% under injection current of 500 mA and by 17.9% and 37.9% under injection current of 1000 mA, respectively. The efficiency droops of the DUV-LEDs with and without the RPL with thick p-GaN were 20.1% and 19.1% and with thin p-GaN were 18.0% and 15.6%, respectively. The DUV-LEDs with the RPL presented improved performance. The above results demonstrate the potential for development of the RPLs for DUV-LED applications.

Differential role of actin-binding proteins in controlling the adipogenic differentiation of human CD105-positive Wharton's Jelly cells.

BACKGROUND: Wharton's Jelly cells (WJCs) can be differentiated into adipocytes by cytoskeletal reorganisation in association with changes in the mechanical properties of cells. METHODS: WJCs subjected to adipocyte induction were observed changes in the cell morphology and alterations in actin filament formation. Transfection with either small interfering RNAs (siRNAs) against formin-2 (FMN-2), tropomyosin-1 (Tm-1), caldesmon (CaD), and profilin (Pro) or a pcDNA6-gelsolin (GSN)-constructed vector in WJCs was used to establish their regulatory roles in controlling adipogenesis. Phenotypic transformation of the cell shape and changes in cell surface adhesion force were determined in WJCs after transformation. RESULTS: The levels of protein and mRNA expression of ß-actin and several key actin binding ptoteins (ABPs) were decreased during the early stage of adipogenic induction but were recovered in the later induction. The siFMN-2, siTm-1, siCaD, and siPro gene knockdown in WJCs caused a widening of the cell shape, while WJCs overexpressing GSN retained a fibroblast cell shape. For both transformations, atomic force microscopy revealed alterations in the biomechanical signals on the cell surface. However, the adipogenic potency was increased after siFMN-2, siTm-1, siCaD, and siPro gene knockdown and decreased during GSN overexpression. CONCLUSIONS: siRNA gene knockdown of siFMN-2, siTm-1, siCaD, and siPro enhances the potency for WJCs commitment to adipocyte, while GSN overexpression modulates the PPAR-γ-independent pathway for the adipogenesis of WJCs. GENERAL SIGNIFICANCE: The phenotypic changes associated with decreased ABP gene expression are critical for regulating the adipogenic differentiation of WJCs through the temporal control of actin filament organisation.