A Novel Experimental Approach to PLE Spectral Measurement in PS: Results and Simulation

Abstract

The detailed study of photoluminescence excitation (PLE) spectra in thick porous silicon (PS) layers is carried out using modified experimental technique. Instead of monochromatic detection usually used, a PLE signal is recorded over the whole emission band from a PS layer. For the first time, this technique allowed us to obtain the reliable PLE data up to far UV range of excitation energy Eexc = 5.4 eV. The PLE spectra showed increasing region below the maximum at Eexc ≈ 4.3 eV, then PLE intensity decreased monotonically. The absorption spectrum for PS layers is extracted from the same PLE data using depth profiling method. Low-energy region of the PLE spectra is satisfactorily simulated in terms of quantum confinement model assuming a constant quantum efficiency and log-normal size distribution of silicon nanocrystallites. The PLE decrease above Eexc ≈ 4.3 eV is discussed assuming that hot electrons may be injected from silicon crystallites to adjacent oxide phase in PS. In this way, leaving electrons give rise to nonradiative losses.