Properties of ultrathin films of porous silicon

Abstract

We have produced films of light emitting porous silicon (LEPSi) thinner than 1 μm, lifted them off the silicon wafer by an electropolishing step, and deposited them onto sapphire windows where they remain attached by van der Waals or electrostatic forces. Although free-standing LEPSi films had been obtained before, our films are one order of magnitude thinner, luminesce strongly, and have excellent mechanical properties because of the sapphire substrate. The important steps in this procedure are discussed, and the structural, chemical, and optical properties of these films as measured using a variety of probes are reported. These films are semitransparent in the visible and thus make several new optical measurements possible. In particular, the results of photoinduced absorption measurements performed with 100 fs time resolution are presented.