Time-resolved radiative recombination in black silicon

Black silicon (b-Si) has been receiving a great deal of interest for its potential to be used in applications ranging from sensors to solar cells and electrodes in batteries due to its promising optical, electronic and structural properties. Several approaches have been used to demonstrate the possibility of producing application quality b-Si, which also exhibits light emission properties. The photoluminescence is a useful technique to identify recombination pathways and thus, enable us to optimize device quality. In this work, we report the results of the radiative recombination dynamics in b-Si produced by a technique involving thermal oxidation, photoresist coating and chlorine plasma etching. An ultrafast blue luminescence component competing with non-radiative recombination at surface defects was identified as no-phonon radiative recombination. This component involves two decay processes with a peak energy at around 480 nm, which have the fast component of about 15 ps followed by a component of around 50 ps lifetime. The emission exhibits a slow process in red spectral region with time constant of 1500 ps. When the surface is smoothed, the lifetime of carriers increased up to 4500 ps and the emission peak blue shifted indicating downsizing in dimensions. The results are correlated with transmission electron microscopy, localized vibrational modes and spectroscopic ellipsometry and interpreted through the presence of quantum confinement at the tip regions of the wires, surface defects and oxide environment surrounding the nanoscale wires.