Enhanced Interfacial-Nucleation in Al-Induced Crystallization for (111) Oriented Si1–xGex(0 ≤x≤ 1) Films on Insulating Substrates

Orientation-controlled Si 1– x Ge x (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 - Si 1– x Ge x /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) Si 1– x Ge x ( x < 0.2) layers are selectively formed. However, increase of Ge-fraction significantly enhances the random bulk-nucleation, which results in poly-crystalline Si 1– x Ge x ( 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 Si 1– x Ge x 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.