Porous silicon

Abstract

Porous silicon (PS) is a nanoporous material obtained by electrochemical etching of crystalline silicon. Since its discovery in the mid 1950s it has been investigated as an active material in a number of research fields. The complexity of silicon electrochemistry, which is not yet completely understood, enables fine-tuning of etched nanoporous structures from the scale of a few nanometers up to tens of microns in a nearly continuous way (Sects. 24.1, 24.2). Historically, porous silicon was investigated for its bright visible luminescence and the possibility of realizing efficient silicon-based light emitters. Later, the shaping of complex photonic crystal (PC) structures led to porous silicon returning to the limelight in the form of silicon-based photonics. In fact, compared with other fabrication technologies (such as physical or chemical deposition methods), electrochemical etching has some fundamental advantages: it is a cheap and fast method that does not require complex facilities; it allows fabrication of complex structures with extremely high optical quality, composed by hundreds of layers; and moreover it enables etching of huge-aspect-ratio (> 100) structures in a short time (Sects. 24.3–24.6). Lastly, applications of porous silicon in optical sensing and drug delivery have maintained interest in porous silicon as an extremely lively field.