Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Enhancement of light extraction from light emitting diodes

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

We first report AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) grown on nano-patterned sapphire substrates (NPSS) prepared through a nanosphere lithography technique. The AlN coalescence thickness on NPSS is only 3 μm due to AlN's nano-scaled lateral growth, which also leads to low dislocation densities in AlN and epi-layers above. On NPSS, the light-output power of a 282-nm UV-LED reaches 3.03 mW at 20 mA with external quantum efficiency of 3.45%, exhibiting 98% better performance than that on flat sapphire. Temperature-dependent photoluminescence reveals this significant enhancement to be a combination of higher internal quantum efficiency and higher light extraction efficiency.

282-nm AlGaN-based deep ultraviolet light-emitting diodes with improved performance on nano-patterned sapphire substrates

Recently, thin film solar cells enhanced by nanoparticles have attracted much attention of the scientific community. To improve the performance of such cells, a systematic study on the influence of the nanoparticle material on the efficiency of the enhancement is performed. Based on optimization of the nanoparticle array parameters, the role of dispersion and dissipation of the nanoparticle material is discussed and analyzed with respect to optical absorption of the photoactive layer. Finally, it is demonstrated that the use of dielectric nanoparticles can lead to similar and even higher enhancements compared to that of metal nanoparticles.

Nanoparticle-enhanced thin film solar cells: Metallic or dielectric nanoparticles?

In this study we develop an efficient light harvesting scheme that can enhance the efficiency of GaAs solar cells using self-assembled microspheres. Based on the scattering of the microspheres and the theory of photonic crystals, the path length can be increased. In addition, the self-assembly of microspheres is one of the simplest and the fastest methods with which to build a 2D periodic structure. The experimental results are confirmed by the use of a simulation in which a finite-difference time-domain (FDTD) method is used to analyze the absorption and electric field of the 2D periodic structure. Both the results of the numerical simulations and the experimental results show an increase in the conversion power efficiency of GaAs solar cell of about 25% when 1 microm microspheres were assembled on the surface of GaAs solar cells.

Efficiency enhancement in GaAs solar cells using self-assembled microspheres.

This letter describes the improved output power of GaN-based light-emitting diodes (LEDs) formed on a nanopatterned sapphire substrate (NPSS) prepared through etching with a self-assembled monolayer of 750-nm-diameter SiO2 nanospheres used as the mask. The output power of NPSS LEDs was 76% greater than that of LEDs on a flat sapphire substrate. Three-dimensional finite-difference time-domain calculation predicted a 40% enhancement in light extraction efficiency of NPSS LEDs. In addition, the reduction of full widths at half maximum in the ω-scan rocking curves for the (0 0 2) and (1 0 2) planes of GaN on NPSS suggested improved crystal quality.

Improved output power of GaN-based light-emitting diodes grown on a nanopatterned sapphire substrate

A light-emitting diode (LED) apparatus includes a thermoconductive substrate, a thermoconductive adhesive layer, an epitaxial layer, a current spreading layer and a micro- or nano-roughing structure The thermoconductive adhesive layer is disposed on the thermoconductive substrate The epitaxial layer is disposed opposite to the thermoconductive adhesive layer and has a first semiconductor layer, an active layer and a second semiconductor layer The current spreading layer is disposed between the second semiconductor layer of the epitaxial layer and the thermoconductive adhesive layer The micro- or nano-roughing structure is disposed on the first semiconductor layer of the epitaxial layer In addition, a manufacturing method of the LED apparatus is also disclosed

Light-emitting diode apparatus and manufacturing method thereof

The output power enhancement of the GaN-based light-emitting diodes (LEDs) featuring two-dimensional (2D) hole arrays is demonstrated. The 2D air hole arrays were first generated in the photoresist by utilizing the focusing nature of microspheres, and then transferred onto the GaN surface through dry etching. The maximum output power of the surface-textured LEDs was enhanced by 45% compared with the LEDs without surface texturing. The finite-difference time-domain calculation was performed and revealed that the light extraction efficiency of the textured LEDs increased with increasing etching depth.

Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres

We propose a novel technique to fabricate a free-standing three-dimensional colloidal crystal by self-assembling the colloidal microspheres with controllable thickness from the air–liquid interface. Highly ordered three-dimensional colloidal crystals are formed by polymethylmethacrylate or polystyrene monodisperse microspheres. We also demonstrate the fabrication technique of the free-standing inversed opals by removing the microspheres using calcination. The free-standing colloidal crystal structures can be used for nano-photonic circuits, white-light LEDs or as a photocatalyst.

https://iopscience.iop.org/article/10.1088/0957-4484/16/9/003/pdf

Chia Hua Chan

Papers

Efficiency enhancement in GaAs solar cells using self-assembled microspheres.

Improved output power of GaN-based light-emitting diodes grown on a nanopatterned sapphire substrate

Light-emitting diode apparatus and manufacturing method thereof

Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres

Self-assembled free-standing colloidal crystals