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An analysis of LED and OLED technology and market growth

By Dr. Nisa Khan

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Illumination-industry leaders see broad-use, LED-lamp applications as a real possibility, but on a 10-year horizon, if not sooner. Already, LEDs have overtaken the incumbent lamps in traffic lights; some automotive head, tail and interior lights; signage channel letters and specialized, architectural-lighting applications. In most instances, lighting specifiers utilize inorganic, III-V compound-semiconductor LEDs – they see organic LEDs (OLEDs) as less-mature counterparts, at least for the present.
LEDs aren’t yet the overwhelming choice in various lighting and illumination markets, although they’re commonly applied in electronic billboards and other large-format indoor and outdoor displays. Their considerable viewing distances allow for coarse resolution (pixel pitch), which is achieved with individual, RGB-packaged LEDs (the more mature, inorganic III-V semiconductor type) placed in proximity.
However, smaller, consumer-electronic devices that require higher-resolution screens, such as handheld cellphones, cameras and MP-3 players, as well as prototype laptops and television screens, OLEDs are chosen above the III-V LEDs. Why?
Because a planar array of uniform, high-quality LEDs arranged in the tight proximity needed to form a smaller, but high-resolution viewing screen isn’t possible with III-V semiconductors. The reasons are multifold.
First, high-quality, RGB LEDs come from different III-V compound materials; therefore, monolithic integration of three-color pixels in a single, flat plane isn’t feasible. A hybrid integration of inorganic RGB LEDs with a 16-micron pixel pitch, with adequate color isolation, is a daunting task (16-micron pitch is needed to achieve the 160 pixel/in. required in 1920 x 1200 WUXGA laptop screen; 1 micron = 1/1,000 cm).
Even if such RGB pixels could be constructed in a III-V plane, they would be limited to the 2-in. standard wafer size used in this industry. Currently, only a few high-end, LED manufacturers have 3- or 4-in., wafer-processing capacities, which is still rather small for close-viewing or consumer-device display technologies.