Development of amorphous SiC light emitting diodes

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The aim of this research program is to develop thin-film light emitting devices based on amorphous Silicon Carbide (a-Sic) p-i-n junction structure. Each layer was formed successively on TCO glass substrate by plasma CVD. The band gap of luminescent i-layer is usually adjusted larger than 2.5 eV for allowing visible light emissions, while those of a and p injection layers should be less than 2 eV due to an essential limitation of doping efficiency. Clearly, in this case, the LED performance is governed by the carrier injection efficiency, and tends to be quite poor. to overcome this situation, our focus of efforts has been placed on the development of alternative new injection layers. Several approaches were tried, among which two particular methods yielded good results; i) inserting a wide band gap a-SiC at p/i and i/n interfaces, which works as a tunneling injector, and ii) adopting highly conductive and wide band gap micro-crystalline SiC produced by ECR plasma CVD. In each case, remarkable improvements were achieved in emission color as well as in emission intensity. Combining these two technologies, luminance exceeding 20 cd/m^2 was attained on a yellow-emission LED under the operation voltage of around 10 volts. The technologies developed in this research program will lead to the realization of high-brightness, full color a-SiC thin-film LEDs for large-area displays.