Luminescence from porous silicon

Predominantly orange-red, but occasionally green, blue or deep red luminescence is observed following electrochemical etching of p-type epitaxial silicon in HF solution. Photoluminescence and cathodoluminescence of the same samples are compared. The dependence of the photoluminescence spectrum on the sample temperature and on the excitation density, considered together with its nonexponential decay profile, suggest that the dominant luminescence process in porous silicon is recombination of quantum-confined carriers in a disordered medium. In addition, cathodoluminescence reveals the presence of 'hot spots' which show bright features of uncertain origin.