Previous studies of the Ga doping of β-FeSi2 films had proved, using the molecular beam epitaxy method, that Ga atoms could be an effective p-type dopant. However, there was a crucial problem of extensive pin-hole generation when a high concentration of Ga atoms was introduced into the films. Here, a qualitative investigation of Ga diffusion in β-FeSi2 layers was performed by using secondary ion mass spectroscopy and Auger electron spectroscopy. It was found that Ga atoms diffused much faster in the β-FeSi2 layers than in Si, and tended to congregate at the front surface of β-FeSi2 films during post thermal annealing (800C). The Ga was supposed to evaporate from the surface. On the basis of the results, it was assumed that the formation of pin-holes might be closely related to Ga diffusion and evaporation in β-FeSi2 layers during annealing. In order to suppress the evaporation of Ga, an SiO2 capping layer (about 500nm in thickness) was deposited onto Ga-doped Fe/Si multi-layers prior to annealing. The preliminary results demonstrated that the pin-hole density was reduced by a SiO2 capping layer.

Studies of Ga Diffusion and the Elimination of Pinholes in Ga-Doped β-FeSi2 Films Prepared by MBE. R.Kuroda, Z.Liu, Y.Fukuzawa, Y.Suzuki, T.Ootsuka, S.Wang, M.Osamura, N.Otogawa, Y.Hoshino, Y.Nakayama, H.Tanoue, Y.Makita: Optical Materials, 2005, 27[5], 929-34