ZnSe-based white LEDs

The first phosphor-free white LED based on II-IV compound materials is demo nstrated. Our device utilizes a phenomenon unique to ZnSe homoepitaxy, wher e a portion of the main greenish-blue emission from the active layer of a p n junction diode is absorbed by the conductive substrate which in turn give s off an intense broad-band yellow emission centered around 585 nm by photo luminescence. These two emission bands combine to give a spectrum which app ears while to the naked eye. A typical ZnSe-based white LED lamp exhibits a color temperature of approximately 3400 K with a CRI (color rendering inde x) of 68. The optical output power and operating voltage of such a device a t a forward current of 20 mA is 2.0 mW and 2.7 V, respectively. The luminou s efficiency estimated from these results is 10.41 m/W, which is comparable to the incandescent lamp as well as the commercial InGaN-based white LED. Device lifetimes (half-life) have exceeded 800 h at 20 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.