Deep ultraviolet light-emitting diodes (DUV LEDs) (<280 nm) have been important light sources for broad applications in, e.g., sterilization, purification, and high-density storage. However, the lack of excellent transparent electrodes in the DUV region remains a challenging issue. Here, we demonstrate an architectural engineering scheme to flexibly tune the work function of Cu@shell nanowires (NWs) as top transparent electrodes in DUV LEDs. By fast encapsulation of shell metals on Cu NWs and a shift of electron binding energy, the electronic work function could be widely tailored down to 4.37 eV and up to 5.73 eV. It is revealed that the high work function of Cu@Ni and Cu@Pt NWs could overcome the interfacial barrier to p-AlGaN and achieve direct ohmic contact with high transparency (91%) in 200-400 nm. Completely transparent DUV LED chips are fabricated and successfully lighted with sharp top emission (wall-plug efficiency reaches 3%) under a turn-on voltage of 6.4 V. This architectural strategy is of importance in providing highly transparent ohmic electrodes for optoelectronic devices in broad wavelength regions.
In this paper,luminescence of polypropylene films under dc electric field is studied by using the electroluminescence measuring experiments.The luminescence characteristic under high electric field of polymer films, and the effect of electric field on luminescence are investigated.Experimental results show that the luminescence intensity of polypropylene films increase along with the electric field and higher the electric field is,the higher the kinetic energy of charge carriers injected from the two electrodes are and the easier the collision of charge carriers with luminescence center become,turning energy into the excitation process.Under 3.9MV/cm,the luminescence intensity hardly change,until 4.0MV/cm,while luminescence intensity increase so acutely that prebreakdown phenomenon occurs.
Spin injection performance in GaN film was systematically investigated through the three-terminal Hanle spin precession measurements with the comparison of varied tunnel barrier thickness, spin injector materials, and channel widths. Spin relaxation time and diffusion length were optimized to 37.3 ps and 139.0 nm at room temperature, respectively. With the optimal spin injector, a 12% spin polarization was obtained in a four-terminal non-local spin valve device. By applying the optimized spin injector structure to the spin-light emitting diodes, room temperature circular polarization ratios of 6.2% and 9.2% for Co and Fe spin polarizers were respectively achieved at surface-emission.
Abstract Merons are a class of topologically protected particle-like structures created in in-plane magnetized magnetic films. The structures can act as information carriers and could be used for magnetic storage. However, the development of such applications is hampered by limitations in the size, thermal stability and magnetic-field requirements of the systems. Here we report the construction of millimetre-scale meron lattices that are stable at room temperature and under zero magnetic field. Our system is based on a trilayer structure composed of a thin iron film sandwiched between films of palladium and magnesium oxide (Pd/Fe/MgO) on a gallium nitride wafer. It is fabricated using a molecular-beam epitaxy approach that is assisted by a high magnetic field, which leads to a strong Dzyaloshinskii–Moriya interaction. The lattices can be used for chirality transfer from merons to electrons and then to photons, and we show that the meron lattices can be used as spin injectors in nitride-based light-emitting diodes. The topology-induced spin light-emitting diode can provide 22.5% circularly polarized electroluminescence at room temperature and under zero magnetic field.
Two types of high‐voltage flip chip deep ultraviolet light emitting diodes (HV‐FC DUV‐LEDs) are constructed with 2 × 2 and 3 × 3 cells, respectively, in which each single cell is fabricated with inclined sidewalls covered by SiO 2 /Al. The simulation results suggest that the structure with inclined sidewalls is much favorable to extract the transverse magnetic‐polarized lights. As a result, the light power as high as 145.7 mW is achieved in HV‐FC DUV‐LED constructed with 3 × 3 cells at 1000 mA.
The internal quantum efficiency of blue LEDs is almost close to the limit, therefore, advanced transparent electrode has been long explored for gaining high external quantum efficiency. However, work function mismatch at electrode-semiconductor interface remains the fundamental difficulty in obtaining low resistance ohmic contact. Here, we demonstrate the gas phase encapsulation of graphene layer on superfine Cu nanowires network by chemical vapor deposition for highly transparent LEDs. The fast encapsulation of graphene shell layer on Cu nanowires achieves high optoelectronic performance (33 Ω/sq @ 95% T), broad transparency range (200~3000 nm) and strong antioxidant stability. A novel phenomenon of scattered-point contact is revealed at the Cu nanowires/GaN interface. Point discharge effect is found to produce locally high injection current through contact points, which can effectively overcome Schottky barrier and form ohmic contact. The transparent LED on Cu@graphene nanowire network is successfully lighted with bright blue emission.
Summary form only given: Bulk AlN substrates are an ideal solution for the growth of ultraviolet-C light emitting diodes (UVCLED). They are optically transparent at this wavelength and closely lattice and thermally expansion matched to the layers required for the device structure. In addition pseudomorphic growth can be achieved allowing for low dislocation density in the active region of the device. This approach has been used to achieve the best efficiency and output power, as well as lifetime, in the 265 nm wavelength range. However, currently these substrates are only available in limit quantities and sizes preventing large scale manufacturing such as is occurring with visible LEDs. Regardless, we have been able to succeed in setting up pilot production of UVCLEDs to enable low volume manufacturing and allow for rapid increase in volumes as supply and size of the AlN substrates are increased. This pilot production line utilizes the bulk substrate manufacturing and epitaxial growth at Crystal IS and the high volume fabrication facility at Sanan Optoelectronics. The current process uses 10 x 10 mm 2 AlN substrates. The epitaxial growth process as tracked using both non contact sheet resistance measurements and X-ray diffraction for analyzing the variation in aluminum content of the n type AlGaN layer of each wafer. The sheet resistance and Al content over several lots of wafers is shown. The sheet resistance shows a normal distribution with a mean of 341 ohms/sq. and dispersion of 89 ohms/sq. This value is desired to be as low as possible but in the current range is more than adequate for high performance UVCLEDs. The Al content is targeted at 70% with an upper specification limit (USL) of 75% and a lower specification limit (LSL) of 65%. The distribution is bimodal but does have a mean value of 70.0% and a dispersion of 2.2% indicating the Al% is well controlled with the specification limits. The fabrication process is similar to high volume production of visible LEDs but differs in several key areas. As fabrication facilities are moving beyond 2" substrates and relying on more sophisticated automation to improve yields, the processing of 10x10 mm 2 substrates presents challenges in wafer handling and processing. We have been successful in implementing the fabrication of these wafers in pilot production. By carefully tracking key process parameters such as etch depths, metal thickness, and contact resistances devices can be fabricated with optimal parameters. The output power measured on wafer after the fabrication process is shown. This output power is measured through the partially absorbing AlN substrate at 100 mA of input current and typically at an emission wavelength of 265 nm. This results in a mean output power over 1 mW. This value can be increased significantly once the device is packaged and we have currently demonstrated over an order of magnitude improvement by introducing enhanced photon extraction methods to the device. Additional parameters such as forward voltage and wavelength will be discussed.
GaN-Based Blue Laser Diodes In article number 2400119, Wenyu Kang, Junyong Kang, and co-workers develop an anti-aging technology for high-power GaN LD from mechanism investigation to degradation suppression. This cover depicts a person in different aging stages, indicating the severe degradation issues in high-power LD and the effectiveness of this anti-aging technology.
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