Porous silicon (PS) fabricated by anodizing have recently become the subject of intense interest due to their room temperature visble light emission properties.However, highly porous silicon made by electrochemical etching is fragile and tends to craze during normal drying in air after taken out from HF based solution. The preparation of highly porous materials by sol-gel processing followed by supercritical drying was carried out by Kistler in 1931. Since 1985, the sucpercritical drying (SD) has been used successfully to prepare a variety of aerogels, comprising a void fraction of more than 90%. This technigue has now been applied to prepare luminescent porous silicon on both <100> and <111> C-Si substrates. Porosities up to 94% have been achieved, which were determined by gravimetric measurement. Its morphological feature, microstructure and photoluminescence properties exhibit novel characteristics from those conventionally anodized porous silicon. It has been demonstrated that anodization and supercritical drying can yield ultra-high porous luminescent PS with minimal damage and much higher degree of perfection than that of previously attained. It is very interested that the PL intensity may be inproved by SD method.
