Researchers at the University of California, Santa Barbara, have developed a novel device structure that reduces light absorption inside an LED, enables uniform light emission from the active layer, and reduces light reflections occurring repeatedly inside the LED, thus increasing the overall efficiency.
Current methods of improving efficiency in nitride LED systems, such as the use of a thin nickel, gold, or zinc oxide layer growth to produce transparent electrodes, lack the surface feature shaping capabilities needed to optimize light extraction.
What the researchers at the University of California, Santa Barbara have done is combine an (Al, Ga, In)N and ZnO direct wafer bonded LED with a shaped plastic optical element in which the directional light entering the optical element from a ZnO cone is extracted to air. In particular, the LED structure is combined with a tapered lens, in which most of the light entering the lens lies within the critical angle and is extracted. The device reduces reflection from the plastic encapsulant surface, reduces reflections from the ZnO surface, reduces light absorption inside the LED, enables uniform light emission from the active layer, and reduces light reflections occurring repeatedly inside the LED. As a result, this combined structure extracts more light out of the LED and is thus more efficient than standard LEDs. In addition, the fabrication method may require fewer process steps due to the ease of electrode formation. This LED is applicable to solidstate lighting and other optoelectronic applications.
Some of the advantages this new device structure has over conventional technology are:
- Optimized light extraction (about 500% increase in output power compared to that of a standard square gallium nitride chip at 460nm wavelength and 20mA drive current);
- Highly efficient due to reduction of light absorption in the LED;
- Reduced number of fabrication steps due to ease of electrode formation.
This technology is patented (U.S. patent # 7,994,527) and is available for licensing.