Abstract
Orientation-controlled Si1–xGex (0 ≤ x ≤ 1) films on insulating substrates are essential to achieve high-efficiency solar-cells and high-speed thin-film-transistors. We investigate Al-induced crystallization of amorphous-Si1–xGex/Al-oxide/Al/quartz stacked-structures as a function of Ge-fraction, air-exposure time of Al surfaces, and thicknesses of Al and SiGe films. By tuning interfacial Al-oxide layer thickness, which is controlled by air-exposure time, (100) or (111) Si1–xGex (x < 0.2) layers are selectively formed. However, increase of Ge-fraction significantly enhances the random bulk-nucleation, which results in poly-crystalline Si1–xGex (x ≥ 0.2) with random-orientations. To enhance interfacial-nucleation at Al/quartz over bulk-nucleation, film-thickness of Al and SiGe are thinned to 50 nm. This achieves (111)-oriented Si1–xGex films with the whole Ge fractions. This oriented-growth can be explained by the theoretical calculation that (111) SiGe has the minimum surface energy on quartz substrates.
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