Improved steady-state photocarrier grating in nanocrystalline thin films after surface-roughness reduction by mechanical polishing

Abstract

We detect elastic optical scattering resulting from the surface roughness of nanocrystalline silicon by a poor optical grating in the steady-state photocarrier grating experiment. The small variation of the experimental sampling function reduces the reliability of the ambipolar diffusion length measurements in this case. We demonstrate that the reduction in surface roughness of nanocrystalline silicon by polishing reduces optical scattering, improves the grating quality, and allows a reliable determination of the ambipolar diffusion length, making the experiment attractive for characterizing nanocrystalline silicon and other semiconductors which exhibit optical scattering.

Investigation of meta- and in-stability effects in hydrogenated microcrystalline silicon thin films by the steady-state measurement methods

“…Minority carrier diffusion length, L D , obtained from the fits to experimental data are strongly affected by DI water treatment similar to what has been observed after oxygen treatment and following vacuum process. The only difference for the rough samples is that the grating quality parameter decreased to 0.1-0.2 levels because of increased optical scattering as reported previously [6,17]. L D was found to be 189 nm in the air exposed state and decreased to 175 nm in the annealed1 state.…”

Instability effects in hydrogenated microcrystalline silicon thin films

“…Due to the increased optical scattering the quality of the interference pattern decreases as has been determined on µc-Si:H films with a rough surface on smooth substrates by an analysis of the so-called grating quality factor γ 0 [11].…”

Analysis of the steady-state photocarrier grating method for the determination of the density of states in semiconductors

“…1.01ϫ 10 19 6.40ϫ 10 −7 5.84ϫ 10 −9 7.13ϫ 10 −9 7.20ϫ 10 −9 5.01ϫ 10 −9 1.01ϫ 10 20 5.77ϫ 10 −7 2.32ϫ 10 −9 3.90ϫ 10 −9 3.92ϫ 10 −9 1.99ϫ 10 −9 1.01ϫ 10 21 4.84ϫ 10 −7 0.86ϫ 10 −9 2.19ϫ 10 −9 2.31ϫ 10 −9 0.58ϫ 10 −9 1.01ϫ 10 22 2.90ϫ 10 −7 0.36ϫ 10 −9 0.97ϫ 10 −9 1.23ϫ 10 − The limits and accuracy of the method are two points on which we would like to insist. For instance, it is obvious that the grating period ⌳ lim giving the ␤ lim value is sampledependent, since it will depends on the p p value.…”

“…The factor ␥ 0 , which takes values between zero and one, accounts for the grating quality due to partial coherence of the beams, mechanical vibrations or light scattering. 16,20 The nonuniform illumination leads to a spatially modulated generation rate, G͑x͒ = G 0 + ⌬G cos͑kx͒ = G 0 + Re ⌬Ge jkx , k =2 / ⌳, j 2 = −1, and Re meaning the real part of the complex number. This spatially modulated generation rate in turn creates free electrons and holes distributions, n͑x͒ and p͑x͒, with the same period.…”

“…The technique became a standard method for material characterization in several laboratories, and it was applied not only to amorphous silicon and its alloys [16][17][18] but also to microcrystalline silicon 19,20 and to crystalline materials. 16,21 Several authors analyzed different aspects of the SSPG method, contributing to an understanding of the physics involved.…”