A simple, low-cost, and non-vacuum epitaxial growth method to realize large-area semiconductors on crystalline silicon will become the game-changer for various applications. For example, we can expect the disruptive effect on the cost of large-scale III-V multi-junction solar cells if we could replace the high-cost germanium substrate with silicon-germanium (SiGe) on Si. For SiGe epitaxial growth, we attempted to develop a process using original Al-Ge pastes for screen printing and subsequent annealing. We compare two pastes including Al-Ge alloyed pastes with compositional uniformity in each particle and Al-Ge mixed pastes. We revealed that Al-Ge alloyed paste could form flatter SiGe film with much less residual pastes, supported by in-situ observations. The uniform and sufficient dissolution of the alloyed paste is responsible for these and led to higher average Ge-composition by annealing at 500 °C. The composition in SiGe was vertically graded up to ~ 90% at the topmost surface. These results show that printing and firing of Al-Ge alloyed paste on Si is the desirable, simple, and high-speed process for epitaxial growth of SiGe, which could be potentially used as the lattice-matched virtual substrate with III-V semiconductors.
The electrodeposition of invar Fe-Ni alloy with low thermal expansion was performed at 100-5000 A·m–2 and 105 C·m–2 in agitated Watt’s solution containing NiSO4, NiCl2, FeSO4, C3H4O4, C7H4NNaO3S and H3BO3 at 50ºC. With increasing the concentration of malonic acid, the Ni content in deposits decreased at higher current density region than 2000 A·m–2, while it increased at lower current density region than 1000 A·m–2. The current efficiency for alloy deposition decreased with increasing the concentration of malonic acid. The deposits were composed of granular crystals whose size decreased with increasing the concentration of malonic acid. With an addition of saccharin, the Ni content in deposits significantly decreased, and the current efficiency for alloy deposition increased. With an addition of boric acid, the Ni content in deposits somewhat decreased, and the current efficiency for alloy deposition increased. The surface morphology of deposits changed with the current density and an addition of saccharin, and rarely changed with an addition of boric acid. It was found that the morphology depended on the Ni content in deposits. The deposits with Ni content of 29-38 mass% were composed of granular crystals approximately 300 nm in size, while the deposits with Ni content of 41-52 mass% showed the smooth surface consisted of fine crystals. The effects of additives on the Ni content in deposits and current efficiency can be explained by the change of partial polarization curve for Fe and Ni deposition and hydrogen evolution in Fe-Ni alloy deposition.
