Influence of Substrate on Crystal Orientation of Large-Grained Si Thin Films Formed by Metal-Induced Crystallization

Kaoru Toko,Masato Sasase,Mitsuki Nakata,Takashi Suemasu,Noritaka Usami,Atsushi Okada

doi:10.1155/2015/790242

Abstract

Producing large-grained polycrystalline Si (poly-Si) film on glass substrates coated with conducting layers is essential for fabricating Si thin-film solar cells with high efficiency and low cost. We investigated how the choice of conducting underlayer affected the poly-Si layer formed on it by low-temperature (500°C) Al-induced crystallization (AIC). The crystal orientation of the resulting poly-Si layer strongly depended on the underlayer material: (100) was preferred for Al-doped-ZnO (AZO) and indium-tin-oxide (ITO); (111) was preferred for TiN. This result suggests Si heterogeneously nucleated on the underlayer. The average grain size of the poly-Si layer reached nearly 20 µm for the AZO and ITO samples and no less than 60 µm for the TiN sample. Thus, properly electing the underlayer material is essential in AIC and allows large-grained Si films to be formed at low temperatures with a set crystal orientation. These highly oriented Si layers with large grains appear promising for use as seed layers for Si light-absorption layers as well as for advanced functional materials.

Highlights

High-quality crystalline Si on glass has been widely studied for use in low-cost thin-film solar cells with high-conversion efficiencies [1, 2]
These energy dispersive X-ray spectroscopy (EDX) maps show that the layer exchange between the Al and Si layers occurred during annealing, causing Si to stack on AZO
We investigated how underlayers affected the crystal quality of aluminum-induced crystallization (AIC)-Si in order to obtain high-quality polycrystalline Si (poly-Si) on a conducting-layer-coated glass substrate

Summary

Introduction

High-quality crystalline Si on glass has been widely studied for use in low-cost thin-film solar cells with high-conversion efficiencies [1, 2]. To form polycrystalline semiconductors on glass, aluminum-induced crystallization (AIC) is a possible technique that has received much attention [7, 8]. In this technique, an amorphous Si (a-Si) layer on an Al layer is transformed into a crystalline phase via exchange between the Al and Si layers during annealing at low temperatures (425–500∘C) [9,10,11]. AIC can grow either (100)- or (111)-oriented poly-Si films with large grains (diameters of 10–100 μm) by controlling the initial Al thickness [11], the interface between the Al and Si [12], and the growth temperature [13, 14]. AIC-Si is being researched as a seed layer for homoepitaxial growth of a Si light-absorption layer to obtain high-efficiency thinfilm solar cells [2, 15, 16]

Results

Discussion

Conclusion