Improved Surface Quality of the Metal-Induced Crystallized Ge Seed Layer and Its Influence on Subsequent Epitaxy

Abstract

Al-induced crystallized Ge (AIC-Ge) seeded epitaxy is a promising way to fabricate functional materials on amorphous substrates such as glass or polymer sheets. However, the AIC-Ge had difficulty in producing a continuous thin film without forming fine-grain Ge islands stacked on the surface. In this paper, we solved this problem by initially preparing thicker Ge (100 nm) than Al (50 nm) and then removing excess Ge islands using a unique etching technique. The resulting AIC-Ge allowed for a high ( 111) orientation (96%) and large grains (>100 μm). Transmission electron microscopy demonstrated that an AIC-Ge-seeded Ge layer, grown by molecular-beam epitaxy at 500 °C, was of high quality reflecting the annihilation of Ge islands. This method opens up the possibility for synthesizing Ge, GaAs, and other functional materials on an amorphous substrate.

Fabrication of Si(111) crystalline thin film on graphene by aluminum-induced crystallization

“…The dendrites seen in the optical images are islands with a height of about 30 nm on top of a 50 nm layer, which corresponds to the original Al thickness. The islands observed in Figures 3(a) and 3(c) are similar to what is observed for the crystallization process of Ge, 24 showing two distinct layers corresponding to the original thickness of Al and a-Si of 50 nm. Figure 3 indicates that the Si(111) film obtained by AIC on graphene is smoother than that obtained 2016) by AIC on SiO 2 with more homogeneity in thickness.…”

High photoresponsivity in a GaAs film synthesized on glass using a pseudo-single-crystal Ge seed layer

“…30 After annealing, the sample was treated in an H 2 O 2 (50%) solution followed by an HF solution (1.5%) to remove "Ge islands" and the Al layer and obtain a good Ge surface. 32 The resulting ALILE-Ge seed layer was highly (111)-oriented and large-grained (>100 lm) as shown in the electron backscatter diffraction (EBSD) images in Figs. 1(b) and 1(c).…”

“…Metal-induced layer exchange is known as a method for forming a large-grained Ge thin film at low temperature on inexpensive substrates such as glass [26][27][28][29][30][31][32] and even plastic. [33][34][35] We achieved highly (111)-oriented Ge thin films with large grains (>100 lm) using Alinduced layer exchange (ALILE).…”

“…[33][34][35] We achieved highly (111)-oriented Ge thin films with large grains (>100 lm) using Alinduced layer exchange (ALILE). 28,32 Because the light absorption thickness for GaAs is approximately 3.5 lm owing to its large absorption coefficient, GaAs grown epitaxially on the ALILE-Ge layer will behave as a pseudosingle crystal. In this study, a pseudosingle crystal GaAs thin film is formed below the heat proof temperature of glass (<550 C) using ALILE-Ge on glass as a seed layer.…”

“…A 50 nmthick Ge seed layer was prepared on a glass substrate using ALILE. 28,32 In the ALILE process, 50 nm-thick Al and 70 nm-thick amorphous Ge (a-Ge) thin films were sequentially prepared on a SiO 2 glass substrate at room temperature using RF magnetron sputtering (base pressure: 3 Â 10 À4 Pa) with Ar plasma. A diffusion-controlling AlO x layer was prepared between the Al and a-Ge layers by air exposure (5 min).…”