TOKYO—Japan Energy Corp. has created a high-purity green-light-emitting diode (LED). The development comes as the result of the company's successful growth of large, single-crystal zinc telluride (ZnTe) and its successful development of a p-n junction.
Zinc telluride has long been considered a prime candidate for LED production. Because it is a direct-transition semiconductor, it can theoretically produce pure green light with high efficiency. However, it has not been commercialized as an LED material because of the difficulty of producing a stable p-n junction.
To grow the crystals, Japan Energy Corp. used a process previously developed for cadmium telluride production called vertical-gradient freezing. The process involves melting the ingredients in a pot and then gradually applying a temperature gradient to the pot to cool it, forming crystals as a result. Because the material is not exposed to the atmosphere, it is subjected to only a small heat stress, suppressing the formation of defects.
This method has resulted in an optically superior single crystal with a low density of defects. At 80 mm in size, the crystal diameter is large. Created using a specially developed heat-processing method, the p-n junction is stable and has a high degree of reproducibility. A sample pure-green-emitting LED was fabricated incorporating the p-n junction. The luminance for the LED compared favorably with the luminance of commercial yellow-green LEDs.
The heat-processing method is simple in principle and can produce LEDs at a lower cost than epitaxial growth methods used in conventional compound-semiconductor LED production. Japan Energy Corp., which plans on full-scale production starting next year, has sent samples of ZnTe crystals to LED makers and is awaiting their responses.
Courtesy O plus E magazine
