Development and Photonic Integration of Efficient and Stable Silicon-Based LED

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To develop efficient and stable silicon-based LED and make the technological foundation of monolithic photonic integration more solid, experimental studies have been conducted in terms of fabrication technique, surface passivation, and related optoelectronic characterization. The major results and their significances are summarized as follows.1. Drastic improvement in the efficiency of Si-based LEDsBy introducing a post-anodization electrochemical treatment, the leakage component in the porous silicon diode current is successfully reduced, and carrier injection into luminescent nanocrystalline silicon becomes very efficient. As a result, the external quantum efficiency is enhanced to beyond 1%. Also, an external power efficiency of 0.4% close to a practical level can be obtained from a diode with an appropriate device configuration. These are the highest values to date in this field. Some key issues for stabilization of LED operation and for tuning the emission band have also been clarified. Especially important result is that blue emission has been observed with oxide-free samples.2. Findings of novel functions of silicon nanocrystalsFrom some electrical and optical investigations, it has been shown that luminescent nanocrystalline silicon exhibits various useful functions : light-emissive nonvolatile memory, ballistic electron emission, and thermally induced ultrasonic emission. Nanocrystalline silicon is very useful as a multi-functional material.3. Toward photonic integrationThe compatibility of nanocrystalline silicon with three-dimensional buried optical waveguide was examined. It has been demonstrated that a buried bent waveguide with an extremely small curvature can be fabricated by simple palanar processing. Nonlinear optical effects due to refractive index change were also observed.