Yen Chin Wang

Warm-white light-emitting diode with high color rendering index fabricated by combining trichromatic InGaN emitter with single red phosphor.

We present a trichromatic GaN-based light-emitting diode (LED) that emits near-ultraviolet (n-UV) blue and green peaks combined with red phosphor to generate white light with a low correlated color temperature (CCT) and high color rendering index (CRI). The LED structure, blue and green unipolar InGaN/GaN multiple quantum wells (MQWs) stacked with a top p-i-n structure containing an InGaN/GaN MQW emitting n-UV light, was grown epitaxially on a single substrate. The trichromatic LED chips feature a vertical conduction structure on a silicon substrate fabricated through wafer bonding and laser lift-off techniques. The blue and green InGaN/GaN MQWs were pumped with n-UV light to re-emit low-energy photons when the LEDs were electrically driven with a forward current. The emission spectrum included three peaks at approximately 405, 468, and 537 nm. Furthermore, the trichromatic LED chips were combined with red phosphor to generate white light with a CCT and CRI of approximately 2900 and 92, respectively.

GaN-based photon-recycling green light-emitting diodes with vertical-conduction structure

A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

Comparative Evaluation of the Imaging Performance of Multi-Primary Color LCDs With RGBCW and RGBCY Pixel Units by Simulation

Through a simulation study, the imaging performance of two types of multi-primary color liquid crystal displays (LCDs) with striped RGBCW (red, green, blue, cyan, and white) and RGBCY (red, green, blue, cyan, and yellow) pixel units is evaluated comparatively. Results show that color consistency and enhanced luminance can be achieved in image rendering with RGBCW rather than RGBCY pixels when the proposed color conversion algorithm is employed. Color measurement by spectrometry is conducted simultaneously to prove that with RGBCW pixels, the color imaging performance is almost as good as that with conventional RGB pixels; the luminance achieved with RGBCW pixel units is higher than that achieved with RGBCY pixel units.

GaN-Based UV Light-Emitting Diodes With a Green Indicator Through Selective-Area Photon Recycling

A light-emitting diode (LED) consisting of an ultraviolet (UV) InGaN/AlGaN multiple quantum-well (MQW) p-i-n structure and a ten-pair green unipolar InGaN/GaN MQW grown on the same sapphire substrate was investigated. After a series of device-processing procedures, including wafer bonding and laser liftoff, the proposed UV LED structure, which features a visible indicator formed through selective-area photon recycling and exhibiting a dual-peak spectrum comprising UV and green peaks, was produced. The green peak originated from UV light generated by the electrical pumping of the epitaxially stacked green MQW. The green light emission may practically be used in indicators and warning signs during the operation of UV LEDs. The current-dependent light output of the green peak may further serve as a reference for measuring the output power of the UV peak of the proposed UV LEDs.

Imaging Evaluation for Simulated RGBW Color LCDs With the Proposed Color Conversion Algorithm

This paper is a comparative evaluation of imaging performance for two types of color liquid crystal displays (LCDs) with Quad RGBW (red, green, blue, and white) and Stripe RGB (red, green, blue) pixel units by means of simulation study. In accordance with the study results, using the proposed color conversion algorithm could achieve color consistence and higher luminance for rendering images with RGBW rather than RGB pixel units. Simultaneously, instrumental color measurement via a spectrometer was done which results also proved that almost same color values of rendering images with RGBW pixel units as well as those images with original RGB pixel units, and higher luminance was achieved. Finally, the pseudocolor phenomenon of rendering images with RGBW pixel units is analyzed and discussed on the basis of human vision model.

A Simulation Study of Improving Viewing Angles Using Composite Uniaxial Compensation Films in Optically Compensated Bend Liquid Crystal Displays

In this study, we use the commercial simulation software, DIMOS2.0, to study improvement of viewing angle performance. Based on concepts of optical phase compensation, optimized conditions of composite uniaxial compensation films are achieved in optically compensated bend (OCB) liquid crystal displays (LCDs). In conditions of D65 illumination for compensated cells, it shows that viewing angles with contrast ratio over 10 are in the ranges of horizontal 100° and perpendicular 130°. No gray scale inversion occurs within polar angle of 70° at horizontal direction. According to definition of CIE 1931, color coordinate of white point in non-compensated and compensated simulated cells are (0.29634, 0.32592) and (0.27143, 0.29306) at on-axis viewing direction, respectively. Contrast ratio is over 3000 at on-axis viewing direction.