Porous silicon for microelectronics and optoelectronics

Abstract

Porous silicon is a material which is obtained by anodic dissolution of monocrystalline silicon in concentrated hydrofluoric acid solutions. Its structure consists of a network of interconnected pores of very small radii (in the range 1.5–20 nm) corresponding to porosities which can be varied up to 90% according to the formation parameters: silicon doping level, electrolyte composition and anodic current density. The formation mechanisms of porous silicon are briefly presented, and the main properties of the material are reviewed. It is shown that they are at the origin of different applications in the field of thin films for microelectronics and for microsensor technology. The interest in porous silicon has been renewed recently by the discovery of a bright emission of visible light at room temperature from high porosity porous silicon films. The main characteristics of this new property, which opens up possibilities for silicon based optoelectronics, are described and discussed in relation to the mechanisms proposed for the light emission. Recent results on the visible electroluminescence which is obtained either from electrolytic cells or from solid devices are also presented.