Abstract
We performed interferometric time-resolved simultaneous reflectance and transmittance measurements to investigate the carrier dynamics in pump-probe experiments on thin porous silicon membranes. The experimental data was analysed by using a method built on the Wentzel-Kramers-Brillouin approximation and the Drude model, allowing us to reconstruct the excited carriers’ non-uniform distribution in space and its evolution in time. The analysis revealed that the carrier dynamics in porous silicon, with ~50% porosity and native oxide chemistry, is governed by the Shockley-Read-Hall recombination process with a characteristic time constant of 375 picoseconds, whereas diffusion makes an insignificant contribution as it is suppressed by the high rate of scattering.
Highlights
Since the 1990s, research interest in Porous Silicon (p-Si) has grown considerably, following reports that showed photoluminescence in the visible range[1,2]
In many cases, p-Si samples are usually composed of a porous silicon layer on top of a crystalline silicon (c-Si) substrate, which might distort accurate estimation of the transport properties[20,21,22]
We show that the carrier dynamics in our samples are governed exclusively by the recombination process, whereas the contribution of the diffusion is insignificant
Summary
Since the 1990s, research interest in Porous Silicon (p-Si) has grown considerably, following reports that showed photoluminescence in the visible range[1,2]. In many cases, p-Si samples are usually composed of a porous silicon layer on top of a crystalline silicon (c-Si) substrate, which might distort accurate estimation of the transport properties[20,21,22] To avoid these problems in this work, we used free-standing thin membranes of p-Si and contactless ultrafast optical methods. The observation of the interferograms is not accidental, but had a deliberate purpose to select the thicknesses of membrane providing a high fringe contrast These well-resolved fringes enhance the optical response of the probe interacting with the optically excited membrane and improve the sensitivity of the experiment; while, without the fringes on thick membranes, the change of the reflectance and transmittance induced by the pump could be too weak to successfully analyse. We estimated the recombination time to be 375 ps
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