Abstract
In this paper, high-quality polycrystalline silicon (poly-Si) thin films on glass substrates are formed by Aluminum-induced crystallization (AIC). In AIC processes, bi-layer structures of amorphous silicon (a-Si) / Al are transformed into ones of (Al+ residual Si)/ poly-Si after simply annealing at 500°C in vacuum furnace. After Al chemical etchings, it isobserved that the obtained structures are poly-Si thinfilms on glasses with some amount of residual Si as“ islands”scattered on theirsurfaces. The number of these “Si islands” remarkedly reduced by choosing an appropriate thickness ratio of pre-annealled Al and Si layers that prepared by magnetron dc sputtering. In this study, at initial Al/a-Si thickness ratio of 110/230 nm, the high-quality poly-Si thin films are formed with very few“Si islands” on the surfaces after AIC processes. Theobtained smooth surfaces are not appearing “dendritic” in optical transmission microscopy (OTM ) images, have large grain size of tens of nanometers in SEM images and have average surface roughness of about 2.8 nm in AFM images. In addition, XRD Ө -2Ө measurements show a strong Si (111) peak at the 2Ө angle of 28.5°, presenting good crystalline phases. The films also reveal good p-type electrical conductivityin that their high carrier concentration and mobility in Hall effect measurements are 1018 cm-3 and 48 cm2/Vs, respectively.
Highlights
Polycrystalline silicon thin films on lowcost substrates prepared by aluminum-induced crystallization (AIC) technique are of great interest for electronic devices, such as solar cells and thin-film transistors
After annealing and chemical etching Al by appropriate acid solution, the samples are evaluated by X-ray diffraction (XRD) measurements, scanning electron microscopy (SEM), optical transmission microscopy (OTM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX) analyses and Hall measurements
Surface morphology After annealing and etching off residual Al by standard acid solution, samples are observed by optical transmission microscopy (Fig. 1)
Summary
Polycrystalline silicon thin films on lowcost substrates prepared by aluminum-induced crystallization (AIC) technique are of great interest for electronic devices, such as solar cells and thin-film transistors. Crystallized Si films can be formed on foreign substrates using AIC at temperatures below the eutectic temperature in Si –Al phase diagram. It is based on the overall layer exchange between adjacent Si and Al films during annealing process, resulting in the transformation from amorphous topolycrystalline Si phases. The obtained poly-Si thin films by AIC often contain “Si islands” on the surfaces [1]. The best poly-Si films, with very little amount of residual Si on the surfaces, are obtained by choosing proper thickness ratio of pre-annealled Al and Si layers in AIC process. After annealing and chemical etching Al by appropriate acid solution, the samples are evaluated by X-ray diffraction (XRD) measurements, scanning electron microscopy (SEM), optical transmission microscopy (OTM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX) analyses and Hall measurements
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