An alternative approach to understand the photoluminescence and the photoluminescence peak shift with excitation in porous silicon (original) (raw)

There have been many different models proposed for the luminescence in porous silicon ͑PS͒, yet it is believed that the quantum confinement effect persists at the absorption. However, from our investigation on both constant and pulsed electrochemically etched silicon ͑PS͒, the absence of quantum confinement effect at the absorption has been identified from the close correspondence of photoluminescence excitation ͑PLE͒ spectra of PS to the simulated absorption spectrum of an ultrathin silicon film with the bulk optical constants. In the simulation of absorption spectrum, the spectral dependence of reflectivity of the solid, which had been omitted in the traditional analysis of PLE, is considered. Further, although nanocrystallites of silicon are present in the PS matrix, the absence of quantum confinement is explained on the basis of structural characteristics of PS. Following that, many common observations in the luminescence of PS are attributed to the surface states. The blueshift of the PL peak with the increase in excitation energy is explained with the idea of quasithermal equilibrium and the probability of occupation of the carriers at the surface states.