Excited carrier dynamics in silicon quantum tips

Abstract: We report on excited states dynamics of silicon quantum tips with sizes down to few atoms at their tapered ends produced by reactive ion etching process of thermally oxidized and photoresist coated Si wafers using... [ view full abstract ]

Abstract: We report on excited states dynamics of silicon quantum tips with sizes down to few atoms at their tapered ends produced by reactive ion etching process of thermally oxidized and photoresist coated Si wafers using chlorine plasma. An ultrafast blue luminescence component competing with non-radiative recombination at surface defect states was quantified as originating from the no-phonon electron-phonon recombination.  This component involves two decay processes with a peak energy at around 500 nm, which have the fastest component of about 6 ps followed by a fast component of about 45 ps decay time constant.  Si quantum tip exhibits also a slow component in the red spectral region with a time constant of about 2.5 ns.  When a quantum tip is oxidized, the slow luminescence band at around 600 nm is enhanced in intensity to the detriment of blue-green emission band. This process results in a much slower states with a time decay of 4.5 ns assuming a 3-component exponential decay as measured by Streak camera.  The ultrafast emission decay leads to a transfer of carriers to long-lived defect states as evidenced by a red emission at around 2 eV.  Red shift at the initial stages of the blue luminescence decay confirms a possible charge transfer to long lived states. Time-correlated single photon counting measurements revealed a life-time of about 5 ns for these states.  The results are discussed in terms of electronic band structure modification at reduced sizes as the core and defects induced at the surfaces involving dangling bonds and oxygen. Related quantum technology applications of these atomic size tips are discussed in terms of quantum information processing hardware such as memories, dots, photon source, sensor and SOI based transistors.