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We have epitaxially grown undoped b-FeSi 2 films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. b-FeSi 2 films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 10 19 cm À3 at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 10 16 cm À3 at RT). The minority-carrier diffusion length was estimated to be approximately 16 lm using an electron-beam-induced current technique; this value is twice as large as that for b-FeSi 2 prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 ls, which is much longer than that for b-FeSi 2 prepared without atomic hydrogen (3 ls). The photoresponsivity reached 13 mA/W at 1.31 lm, which is the highest value ever reported for b-FeSi 2 films.

We have fabricated 200-nm-diameter ferromagnetic resonant tunneling diodes (FM-RTDs) using CaF 2 /Fe 3 Si heterostructures on Si (111)

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The electrical properties of defects in a p-β-FeSi2/n-Si heterostructures were investigated by deep level transient spectroscopy (DLTS) and the electron-beam-induced current (EBIC) technique. DLTS revealed the presence of trap levels for holes, caused by defects in the n-Si layer near the interface during the β-FeSi2 film fabrication. The defect density became small when a 20-nm-thick β-FeSi2 template layer was grown on the n-Si prior to molecular beam epitaxy (MBE) of a 700-nm-thick β-FeSi2 layer. The diffusion length of minority carriers in the n-Si was found to be approximately 15 µm by EBIC. This is much larger than the value of approximately 3 µm for the n-Si obtained when the template layer was not inserted.

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