In this research, experiments and optical simulations are carried out to study the effect of beveled sidewalls and geometric shapes on the light extraction efficiency of a GaN light-emitting diode (LED) with sapphire substrate. In addition to the conventional rectangular chips, hexagonal chips are experimentally processed for the first time on a novel island-like GaN substrate, on which the beveled sidewalls are naturally formed at each island during GaN epitaxial growth on a sapphire original substrate by hydride vapor phase epitaxy (HVPE) technology. The results from our simulations and experiments show that the output power of a LED with beveled sidewalls is about two times that of a normal LED, and those from hexagonal chips are always better than those from conventional rectangular chips.
In this research, experiments and optical simulations have been carried out to study the effect of bevelled sidewalls and geometric shapes on the light extraction efficiency of GaN LED chips. Besides the conventional rectangular chips, hexagonal LED chips were experimentally processed for the fist time on a novel island-like GaN substrate. The bevelled sidewalls could be naturally formed on the chips during the growth of GaN islands by HVPE technology. The results of simulations and experiments are consistent with each other, and show that the output power of LED will be improved doubly when the sidewalls were beveled on the chip. The light output from hexagonal LED chips is also proved better than that from conventional rectangular chips.
KEYWORDS: Light emitting diodes, LED lighting, Solid state lighting, Light sources and illumination, Gallium nitride, Packaging, Lamps, Optoelectronics, Metalorganic chemical vapor deposition, LED displays
This paper reviews the current status of the solid state lighting technology development at the Opto-Electronics & Systems Labs. (OES), Industrial Technology Research Institute (ITRI) and recent industrial activities in the related areas in Taiwan.
White LED is well known as a promising device for solid state lighting. It has the advantages of long life, good endurance of heavy impact, no mercury containing and potentially high efficiency. However, light output from a commercial LED lamp is usually less than 0.1W, which is very small if compared with traditional light sources. In order to get enough light output from LED devices, a big-lamp or cluster, which is packed from dozens or hundreds of LED lamps, is necessary not only for outdoor display but also for lighting applications. Some problems were encountered during high-density assembly in a big-lamp. Because of the bad heat conductivity of the epoxy, the more LED lamps are used in the big-lamp, the poorer heat dissipation will be. On the other hand, it is difficulty to manufacture a big-lamp in good alignment of every LED¡¦s during the package. One of the ways to solve this problem is to use a big LED chip instead of many small lamps. Nevertheless, to use those big chips always companions 10-25% loss in the external quantum efficiency. And, the bigger the chip is, the larger the loss will be. Highly concentrated heat will be another issue for the big chip package.
In this article, we will present a new design for the package of multi-chips LED module, which could assemble dozens of LED chips with the normal size for lighting purpose. Optical devices, including reflector and focusing lens, and heat considerations are considered in the design of the new module. The prototypes of the new modules have been made. The current of maximum light output (Cmax) is about 2 to 3 times superior to conventional lamps. Under the condition of normal driving current, a 4.5 W LED module have an output intensity of 164 cd. Combining 4 LED modules will be comparable with a conventional 20 W Halogen lamp.
A1GaInP visible laser diode is one of the most attractive light sources because it is of great importance in many applications such as optical information storage systems, laser printers, bar code readers and laser pointers. A1GaInP laser diode has a broad emission spectrum of 610 to 690 nm that makes it a versatile and outstanding light source. In addition, AlGaInP laser diodes with low threshold currents have also been realized. The laser diode used for our study is a 660-nm compressively strained A1GaInP with a structure of double-channel ridge waveguide (DCRW). Laser diodes with DCRW structure are widely used for commercialized low-cost and low-power laser diode applications owing to their relatively low threshold currents, easy fabrication and high yield as compared to laser diodes with selectively buried ridge waveguide structure. However, the top surfaces of DCRW laser diodes are non-flat and heat dissipation becomes a main problem for DCRW A1GaInP laser diodes. Especially, if comparing A1GaInP laser diodes with A1GaAs laser diodes, A1GaInP laser diodes have lower thermal conductivity and higher thermal resistance. Therefore, a good die bonding becomes important for improving the heat dissipation of DCRW AlGaInP laser diode chips. Most studies for die bonding have been focused on the choice of submounts or heat sinks with large heat conductivity. Few investigators study how to improve the quality of die bonding and avoid leading voids inside bonded interface. In this study, different p-metal materials, p-metal annealing environments, die-bonding steps and die-bonding equipment were adopted to change die-bonding conditions. Their influences on thermal dissipation capability were also investigated.
A new apparatus is proposed for the package of AlGaInP visible laser diodes (LD) in this paper. Corresponding to the metal-can used in the conventional LD apparatus, plastics and lead-frame are used in this apparatus to reduce its cost. All the chip-mounting and wire- bonding for the apparatus are also modified to accord with the requirement of simplicity and good productivity. An lead-frame with a heat-dissipation tail is specially designed to overcome the poor heat-conductivity problem, which is observed in the common plastic-molded apparatus. The life time of the AlGaInP LD using the new plastic-molded apparatus is about five times longer than that using the common one.
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