Excited Carrier Recombination in Black Silicon

This presentation is on ultrafast photoluminescence recombination phenomena from black silicon consisting of quantum pillars produced by plasma ion etching. An ultrafast blue luminescence component competing with non-radiative recombination at surface defects was quantified as originating from the no-phonon recombination. This component involves two decay processes with a peak energy at around 480 nm, which have the fast component of about 10 ps followed by a component of about 50 ps decay time constant. The emission exhibits also a slow component in the red spectral region with a time constant of about 1.5-2.5 ns. When black Si is oxidized, the slow band at around 600 nm is enhanced in intensity to the detriment of blue-green emission band. This process results in a much slower sates assuming a 3-component exponential decay as measured by Streak camera. The ultrafast PL decay leads to a transfer of carriers to long-lived defect states as evidenced by a red emission at around 2 eV. Time-correlated single photon counting revealed a life-time of about few ns for these states. The results are discussed in terms of band structure modification at reduced sizes and defects at surfaces.