Lifetime measurements on attached epilayers and detached epifoils grown on reorganised porous silicon showing a bulk lifetime exceeding 100 μs

This paper discusses on-going efforts towards reliable lifetime measurements on epilayers and the subsequent decoupling of the bulk and surface recombination components, both while it is still attached to the p+ substrate on which it is grown ("attached epilayer") and after its detachment from the substrate ("detached epifoil"). For the "attached epilayers", microwave photo conductance decay (μ-PCD) and simulation-assisted photoluminescence (sim-PL) were applied together with a variation in the epilayer thickness to evaluate the bulk lifetime (τbulk) and total effective surface recombination velocity (Stot) of p-type epilayers. By applying linear fits to reciprocal effective lifetime versus reciprocal epilayer thickness data, Stot of all samples were reliably extracted, resulting in Stot of ∼265 cm/s in the absence of porous silicon at the epilayer/substrate interface compared to ∼9220 cm/s when present and ∼775 cm/s when shielded by a thin back surface field. Based on these Stot values, sim-PL was used to estimate τbulk to be ∼160 μs in the porous silicon area. For the n-type "detached epifoils", quasi-steady state photo conductance (QSSPC) was used. However, reliable τbulk could not be extracted, despite the lower Stot because τbulk was too high. However, a lower limit to τbulk was estimated to be >138 μs. Such high bulk lifetimes imply bulk diffusion lengths that are an order of magnitude longer than the epilayer thicknesses, potentially leading to high cell efficiencies. © 2013 The Authors.

Jaar van publicatie:2013