Porous silicon luminescence under cathodic polarisation conditions

Abstract

Since the first experimental results concerning the intense visible photoluminescence obtained on highly-porous silicon layers have been published[1], a great deal of work has been devoted to the understanding of this property. Different physical origins have been proposed. Among these hypotheses, the quantum confinement of free carriers taking place inside the silicon nanocrystallites[1,2], forming the body of the highly-porous silicon layers, seems at present to be the most supported one. Such nanometric structures can be obtained either by using electrochemical etching parameters producing high porosity [3] layers or by chemically etching layers of lower porosity[1]. Moreover, the broad luminescence line is commonly attributed to the size distribution of the silicon nanocrystallites which are at the origin of the light emission. An interesting consequence of the quantum confinement model associated with the distribution of crystallite size is the possibility to obtain a selective excitation of the inhomogeneously broadened optical transition. This gives rise to a tunable emission which, again, can be found for the PL [4,5] as well as for the EL [6] of porous silicon.