Zinc oxide (ZnO) is a semiconductor with a bandgap in the UV, making it potentially useful as an alternative to gallium nitride for blue- and UV-emitting laser diodes and LEDs. But p-type doping of ZnO is difficult, and means that instead of getting by with the usual single large semiconductor crystal as an emitter source, ZnO-based emitters rely on the use of nanocrystalline structures, resulting in unusual devices such as random lasers. Now, a group at Dongguk University (Seoul, Korea) and the Institute of Microelectronics Technology (Moscow, Russia) working with ZnO nanorod arrays are creating broadband blue-white LEDs that contain on the order of 109 nanodiodes per square centimeter. The nanodiode crystals are grown vertically on a transparent indium-tin-oxide-coated glass substrate; the crystals are then contacted and fixed to a silicon wafer with transparent epoxy.
The devices, which are 2 × 2 cm in size and have a luminance of 30 cd/m2, currently exhibit a low luminous efficiency of 0.2 lm/W but offer many options to improve this figure. The electroluminescence (EL) is broadband, reaching from 350 to beyond 800 nm under a forward bias of 9 V. The researchers are now working to create a high-efficiency pure-UV version of the LED.
Contact Gennady Panin at [email protected].
