No abstract

We report a new design of the light‐emitting device which can be operated under alternating current source directly. The new type alternating current driven light‐emitting device (AC LED) can increase the radition area in each bias direction to improve the device efficiency by the Wheatstone Bridge (WB) circuit design. WB‐AC LEDs with different designs were fabricated and the electrical and optical characteristics were measured. It is found that the efficiency of the WB‐AC LED is influenced by the varied area ratio of the rectified microchip to the central one because of the different current density and forward bias of each microchip. Additionally, the relationship between the area ratio of microchips and the wall plug efficiency of the WB‐AC LED has also been discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This study investigates the distribution of highly-directional far-field emission on GaN-based ultrathin microcavity light-emitting diodes (uMCLEDs) with photonic crystals (PhCs). The ultrathin 550 nm cavity, PhC lattice constant of 370 nm, and hole depth of 250 nm in the GaN PhC uMCLED provide near single guided mode extraction and a pattern of high directionality radiation. Angular-spectral-resolved electroluminescence measurements reveal photon-band structure agreement with the fundamental mode effective refractive index dispersion curve. In addition, GaN PhC uMCLED increase the output power extraction efficiency by 145.9% (∼2.46×) compared with GaN non-PhC uMCLED, and a directional far-field emission pattern at half intensity of nearly ±15°.

In this study, a GaN-based alternating current light-emitting diode (AC-LED) with 34 numbers of microchips illuminated in each bias direction was fabricated. After calibrating the integration duration, the light output powers of the AC-LED driven by AC and DC were 388.1 and 312.8 mW when the input power was about 1 W, respectively. The flickering illumination mode of the AC-LED driven by AC decreased the heat accumulation and revealed a higher energy utilization efficiency than that of the AC-LED driven by DC. The larger blue shift and smaller full width at half maximum of the AC-LED driven by AC than those of the AC-LED driven by DC were also observed.

Far-field distributions of GaN-based photonic crystal (PhC) film-transferred light-emitting diodes (FT-LEDs) were investigated. The thickness of the device is about 840 nm. The emission wavelength is around 520 nm. The PhC region is a square lattice with a/lambda around 0.5. Angular-resolved measurements in the Gamma-X and Gamma-M directions were made in the polarized-resolved manner. Guided mode extraction behavior in agreement with the two-dimensional free-photon band calculation was observed. In addition, the pseudo-TM behavior for the non-collinearly coupled modes was observed. The azimuthal-mapping of the angular-resolved spectra revealed the evolution of the collinearly and the non-collinearly coupled modes. Furthermore, the light enhancement of approximately 2.7x and the collimation angle about 102.3 degrees were achieved.