By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

LED lamp systems having improved light quality are disclosed. The lamps emit more than 500 lm and more than 2% of the power in the spectral power distribution is emitted within a wavelength range from about 390 nm to about 430 nm.

Led lamps with improved quality of light

III-nitride deep ultraviolet (DUV) light-emitting diodes (LEDs) are identified as the promising candidate for energy-efficient, environment-friendly and robust UV lighting source in the application of water/air purification, sterilization, and bio-sensing. However, the state-of-art DUV LED performance is far from satisfaction for commercialization owing to its low internal quantum efficiency, large current leakage and efficiency droop at high current injection, etc. Extensive efforts have been devoted to properly designing the band structures of such luminescent devices to enhance their output power. In this review, we summarize the recent progress on various energy band designs and engineering of DUV LEDs, with particular of interest is paid on the various approaches in band engineering of the electron-blocking layer, quantum well, quantum barrier and the implementation of many novel structures such as tunnel junctions, ultrathin quantum heterostructures to enhance their efficiency. Those inspirational approaches pave the way towards the next generation of greener and efficient UV sources for practical applications.

https://iopscience.iop.org/article/10.1088/1361-6463/ab4d7b/pdf

Band engineering of III-nitride-based deep-ultraviolet light-emitting diodes: a review

A lateral light emitting diode comprises a layer stack disposed on one side of a substrate, the layer stack including a p-type layer, n-type layer, and a p/n junction formed therebetween. The LED may further include a p-electrode disposed on a first side of the substrate and being in contact with the p-type layer on an exposed surface and an n-electrode disposed on the first side of the substrate and being in contact with an exposed surface of an n+ sub-layer of the n-type layer.

Led with uniform current spreading and method of fabrication

A gallium and nitrogen containing substrate structure includes a handle substrate member having a first surface and a second surface and a transferred thickness of gallium and nitrogen material. The structure has a gallium and nitrogen containing active region grown overlying the transferred thickness and a recessed region formed within a portion of the handle substrate member. The substrate structure has a conductive material formed within the recessed region configured to transfer thermal energy from at least the transferred thickness of gallium and nitrogen material.

Gallium—nitride-on-handle substrate materials and devices and method of manufacture

A nitride semiconductor device includes a silicon substrate, a nucleation layer, a buffer layer, a first type nitride semiconductor stacked layer, a light-emitting layer and a second type nitride semiconductor layer. The nucleation layer is disposed on the silicon substrate. The buffer layer is disposed on the nucleation layer. The first type nitride semiconductor stacked layer is disposed on the buffer layer. The first type nitride semiconductor stacked layer being a plurality of lattice mismatch stacked layers includes a plurality of first nitride semiconductor layers and a plurality of second nitride semiconductor layers. The first nitride semiconductor layers and the second nitride semiconductor layers are stacked alternately, and the first nitride semiconductor layers and the second nitride semiconductor layers are different material. The light-emitting layer is disposed on the first type nitride semiconductor stacked layer. The second type nitride semiconductor layer is disposed on the light-emitting layer.

Nitride semiconductor device

A light emitting diode including a GaN substrate, a first type semiconductor layer, a light emitting layer, a second type semiconductor layer, a first electrode, and a second electrode is provided. The GaN substrate has a first surface and a second surface opposite thereto, and the second surface has a plurality of protuberances, the height of the protuberance is h μm and the distribution density of the protuberance on the second surface is d cm −2 , wherein 9.87×10 7 ≦h 2 d, and h≦1.8. The first type semiconductor is disposed on the first surface of the GaN substrate. The light emitting layer is disposed on a partial region of the first semiconductor layer, and the wavelength of the light emitted by the light emitting layer is from 375 nm to 415 nm. The second semiconductor layer is disposed on the light emitting layer.

Light emitting diode and fabricating method thereof

A nitride semiconductor structure including a silicon substrate, a nucleation layer, a discontinuous defect blocking layer, a buffer layer and a nitride semiconductor layer is provided. The nucleation layer disposed on the silicon substrate, wherein the nucleation layer has a defect density d1. A portion of the nucleation layer is covered by the discontinuous defect blocking layer. The buffer layer is disposed on the discontinuous defect blocking layer and a portion of the nucleation layer that is not covered by the discontinuous defect blocking layer. The nitride semiconductor layer is disposed on the buffer layer. A ratio of a defect density d2 of the nitride semiconductor layer to the defect density d1 of the nucleation layer is less than or equal to about 0.5, at a location where about 1 micrometer above the interface between the nitride semiconductor layer and the buffer layer.

Nitride semiconductor structure

The characteristics of the ultraviolet light-emitting diode (LED) with conventional and specifically designed electron blocking layers (EBLs) are investigated numerically and experimentally in this work. Simulation results show that delicately designed EBLs can not only capably perform the electron blocking function but also eliminate the incidental drawback of obstruction of hole injection caused by the nature of the large polarization field at the c-plane nitride heterojunction. It is shown that the polarization induced downward band bending can be mitigated when the portion of conventional EBL lying adjacent to the active region is replaced by a graduated AlGaN layer. The conduction band profile indicates that this replacement structure could have the capability of electron confinement similar to the conventional structure, and the valence band profile indicates that the spike induced by the polarization field is simultaneously eliminated, assisting the process of hole injection and distribution in the active region. Electron leakage over the EBL is thus obviously reduced, and the consumption efficiency of the injection carriers is improved, as expressed in the distribution of the electron current density. The experimental results show that the light output power can be significantly enhanced from 29.3 mW for the conventional device to 54.7 mW for the LED with the redesigned EBL structure.

Efficiency enhancement in ultraviolet light-emitting diodes by manipulating polarization effect in electron blocking layer

The InGaN-based light-emitting diodes (LEDs) with a roughened backside on the N-face surface of GaN substrate were fabricated through a chemical wet-etching process to increase light-extraction efficiency. The stable crystallographic etching planes were formed as the GaN {1011} planes. When the near-ultraviolet and blue LED were operated as a forward current of 20 mA, the output power of LEDs was improved from 13.2 and 19.9 mW to 25.6 and 24.0 mW, respectively. The different enhanced ratio is attributed to the different transmittance as a function of wavelength is caused from hexagonal pyramid on N-face GaN substrate after wet-etching process.

https://ir.nctu.edu.tw:443/bitstream/11536/18960/1/000294854800003.pdf

Yi-Keng Fu

Papers

Nitride semiconductor device

Light emitting diode and fabricating method thereof

Nitride semiconductor structure

Efficiency enhancement in ultraviolet light-emitting diodes by manipulating polarization effect in electron blocking layer

Study of InGaN-Based Light-Emitting Diodes on a Roughened Backside GaN Substrate by a Chemical Wet-Etching Process