Investigation on Evanescent-to-Propagating Light Transformation Technique in a Patterned Substrate

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The evanescent-to-propagating light transformation phenomenon in a fine ridge structure was investigated by optical techniques. It is found that light-extraction efficiency can be further enhanced by about 1.5 times by depositing a thin SiO_2 film on the ridge surface, due to occurrence of the evanescent wave coupling effect at both the semiconductor-SiO_2 and SiO_2-air interfaces. It is also shown that high spatial directionality could be achieved by localizing the light-emitting area around the ridge center.