Growth mechanism and optical properties of semiconducting Mg2Si thin films

Reactive deposition of magnesium onto a hot silicon substrate (200-500 degrees C) does not result in any accumulation of magnesium or its silicide - the condensation coefficient of magnesium being zero. On the other hand, codeposition of magnesium with silicon at 200 degrees C, using a magnesium-rich flux ratio, gives a stoichiometric Mg,Si film. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited. The Mg2Si layers are polycrystalline with a (111) texture. These stoichiometric silicide films still show a tendency to sublimate; whereas capping with an oxide results in extensive intermixing during annealing. The Mg,Si films thus obtained exhibit optical transparency at sufficiently long wavelength, and an absorption edge. Extraction of the absorption coefficient from the data, and analysis of its energy dependence suggest an indirect bandgap of similar to 0.74 eV, plus direct transitions at similar to 0.83 and similar to 0.99 eV. (C) 2000 Elsevier Science B.V. All rights reserved.