Characterization of porous silicon by infrared spectroscopy

Abstract

The surface of electrochemically etched porous silicon is passivated with hydrogen just after preparation. The surface is gradually oxidized under ambient atmosphere, and the rate depends upon the ambient condition. The chemical and physical changes affect the properties of porous silicon-based devices. Proper understanding of the surface is important, and infrared (IR) spectroscopy is an effective and easy tool for monitoring and/or characterizing the surface state. Silicon is almost transparent to IR light, and hence the convenient transmission measurement is applicable to films and membranes of porous silicon. The measurement technique is first described, and then assignments of absorption bands in the spectra are given for the hydrogen-terminated and oxidized surface. The prevention of oxidation and the functionalization of porous silicon surface are important for many practical uses, where IR measurements can be used to monitor the surface. In addition, methods other than the transmission mode are briefly introduced.