Investigation on a magnesiothermic reduction process for preparation of nanocrystalline silicon thin film

Abstract

Nanocrystalline silicon thin films were successfully prepared via a magnesiothermic reduction process. The initial magnesium content was restricted by the thickness of the film deposited on a quartz glass substrate by magnetron sputtering. After the magnesiothermic reduction process, the Raman spectroscopy results revealed a strong correlation between the thickness of the nanocrystalline thin films and the initial magnesium content. The thickness of the nanocrystalline thin films first increased to a maximum and then decreased as the initial magnesium content was further increased. Based on the solid-state reaction between Mg and SiO 2 , the mechanism behind this phenomenon is explained. In addition, the Raman spectroscopy results showed that the average grain size was almost constant and the crystalline volume fraction was found to be proportional to the silicon content. The band gap of the nanocrystalline silicon thin film was estimated to be 2.94 eV.

Controlled preparation of silicon and magnesium silicide on silica glass substrate through magnesiothermic reduction

“…In the reaction with the magnesium deposited on the substrates, however, it was found from X‐ray diffraction that silicon crystallites are generated . In this case, silicon could be prepared under the condition, in which the amount of magnesium is limited, as well as the cases that have previously been reported …”

“…The magnesiothermic reduction has also been applied to silica glass substrates and quartz crystals . Gutman et al performed the reduction with magnesium powder via the solid‐state reaction at 500‐640°C and found that an intriguing structure is generated .…”

“…In these reactions, however, the formation of silicon has not been clearly reported, while a noticeable fact that the nearest neighbor of the unreacted SiO 2 substrates is always the MgO‐rich phase has been described . After the pioneering works, the magnesiothermic reduction of soda‐lime silicate and silica glass substrates with magnesium deposited on the substrates was reported, in which Raman spectra showed that nanocrystalline silicon was successfully prepared . Ma et al mentioned that the thickness of the deposited magnesium is an important factor to obtain the maximal amount of silicon.…”

“…19,20 The magnesiothermic reduction has also been applied to silica glass substrates and quartz crystals. [21][22][23][24][25][26][27] Gutman et al performed the reduction with magnesium powder via the solid-state reaction at 500-640°C and found that an intriguing structure is generated. [21][22][23] The structure is composed of Mg 2 Si-rich and MgO-rich phases with a few micrometers in thickness and periodically arranged parallel to the surface of the silica glass or quartz crystal.…”

“…[21][22][23][24] After the pioneering works, the magnesiothermic reduction of soda-lime silicate and silica glass substrates with magnesium deposited on the substrates was reported, in which Raman spectra showed that nanocrystalline silicon was successfully prepared. 25,26 Ma et al 26 mentioned that the thickness of the deposited magnesium is an important factor to obtain the maximal amount of silicon. We also performed the reduction of silica glass substrates using magnesium vapor, grains, or films deposited on the substrates.…”