Jpn. J. Appl. Phys. Vol. 37 (1998) pp. L 333–L 335 Part 2, No. 3B, 15 March 1998 c 1998 Publication Board, Japanese Journal of Applied Physics Magnetotransport Properties of a Single-Crystalline β-FeSi 2 Layer Grown on Si(001) Substrate by Reactive Deposition Epitaxy Takashi SUEMASU, Ken’ichiro TAKAKURA, Masaya TANAKA, Tetsuo FUJII and Fumio HASEGAWA Institute of Materials Science, University of Tsukuba, 1–1–1 Tennohdai, Tsukuba, Ibaraki 305, Japan (Received December 10, 1997; accepted for publication February 4, 1998) We report on the magnetotransport properties of a single-crystalline semiconducting β-FeSi 2 layer for the first time. A single-crystalline 5000- ˚ A-thick β-FeSi 2 layer was prepared on Si(001) by a two-step reactive deposition epitaxy (RDE). Magnetotransport measurements showed the occurrence of anomalous Hall effect and negative magnetoresistance in the β- FeSi 2 layer below 77 K. The Arrott plot indicated the possibility that the single-crystalline β-FeSi 2 exhibits ferromagnetic behavior below 15 K. KEYWORDS: β-FeSi 2 , reactive deposition epitaxy (RDE), magnetotransport, anomalous Hall effect, negative magnetoresis- tance 1. Introduction In the past ten years, metal silicides have been extensively studied for many applications such as ohmic contacts and metal-oxide-semiconductor (MOS) gate electrodes. On the other hand, much less is known about semiconducting sili- cides, although they have been proposed as potential materials for new optoelectronic devices. Among them, semiconduct- ing iron disilicide, β-FeSi 2 , has been attracting much atten- tion, because it has a direct band gap of about 0.85 eV (1.46 μm) at room temperature (RT), 1–3) which is near the absorp- tion minimum of silica optical fibers. 4) In addition to that, a Si/β-FeSi 2 light-emitting diode (LED) operating at a wave- length of 1.5 μm was recently realized. 5) The β-FeSi 2 has an orthorhombic structure with a=9.86 ˚ A, b=7.79 ˚ A and c=7.83 ˚ A, and contains 16 Fe atoms and 32 Si atoms in the primitive cell. 6) This complex structure is driven from distortion of the highly unstable fluorite struc- ture of metallic γ -FeSi 2 . The valence-band maximum and conduction-band minimum states of β-FeSi 2 have mainly an Fe d character. 6, 7) This is different from usual semiconduc- tors like GaAs, where the gap is As p to (Ga, As) s. We have reported the epitaxial growth of β-FeSi 2 films on Si(001) by reactive deposition epitaxy (RDE; deposition of Fe on a hot Si substrate), and demonstrated the optimum growth condi- tions. 8, 9) Recently, new diluted magnetic semiconductors (DMSs) based on III-V compounds, 10–12) and epitaxial ferromagnetic metal thin films on semiconductor substrates 13–15) were pre- pared using molecular beam epitaxy (MBE). These are very challenging attempts of incorporating magnetism into semi- conductor circuitry. The combination of magnetic materials with Si is very interesting, because almost all the integrated circuits are based on Si technologies. So far, less work has been devoted to the study concerning the hybrid on Si sub- strates, 15) and in particular there are very few reports, to our knowledge, on the magnetotransport properties of a single- crystalline β-FeSi 2 film. 16) Although Valassiades et al. 17) re- ported that the Hall measurements indicated the ferromag- netic behavior of poly-crystalline β-FeSi 2 film at tempera- tures below 100 K, their analysis is not sufficient as men- tioned below. They determined the ferromagnetic transition temperature from the temperature dependence of normal Hall sure of the MBE system was less than 1×10 −10 Torr and it was kept below 5×10 −9 Torr during the evaporation of Fe. N- type epitaxial Si(001) substrates (5–10 Ω·cm; 20×20×0.50 mm 3 ) with a nominal misorientation angle of less than 0.5 degrees were used. The substrate was cleaned and a thin pro- tective oxide layer was formed by the RCA method. After loading the substrate into the growth chamber, the substrate was heated at 850 ◦ C for 20 min to remove the protective ox- ide, which yielded a well developed 2×1/1×2 RHEED pat- tern. Then, the substrate was heated up to 1000 ◦ C for 20 min to make the surface atomically flat. After cleaning the sur- face, the substrate was cooled and Fe of 99.99% purity was deposited, at a deposition rate of 0.1 ˚ A/s, to grow a 5000- ˚ A- thick β-FeSi 2 layer by a two-step RDE method. The detailed growth procedure will be reported elsewhere. In brief, the two-step RDE method consists of first, the RDE growth of a thin β-FeSi 2 template (200 ˚ A in this case) at 470 ◦ C, follow- ing 30-min annealing at 850 ◦ C in ultrahigh vacuum, and then RDE growth at 850 ◦ C. A total Fe of 1570 ˚ A thickness was de- posited. The thickness of β-FeSi 2 layer was calculated using the densities of Fe and β-FeSi 2 , which contain 8.46×10 −2 and 2.65×10 −2 atoms/ ˚ A 3 of Fe, respectively. Thus, 1 ˚ A of coefficient R 0 deduced from slope of the magnetic field B versus Hall voltage V H characteristics at B =1.5 T. How- ever, the magnetic field of 1.5 T is not sufficient to separate R 0 from an anomalous Hall coefficient R S , because R S does not saturate at B =1.5 T in the B versus V H characteris- tics. And also, the negative magnetoresistance was very small compared to III-V DMSs. This is due to the inferior quality of the poly-crystalline β-FeSi 2 film. Thus, in order to clarify the magnetotransport properties of β-FeSi 2 , it is necessary to grow a single-crystalline β-FeSi 2 film. In this letter, we report on the magnetotransport properties of a 5000- ˚ A-thick single-crystalline β-FeSi 2 film on an n- Si(001) substrate prepared by a two step RDE method, where the clear anomalous Hall effect and large negative magnetore- sistance are observed. In addition, we estimate the possible ferromagnetic transition temperature from the Arrott plot. 2. Experimental An ion-pumped MBE system equipped with a 30 keV re- flection high-energy-electron diffraction (RHEED) and elec- tron gun evaporation source for Fe was used. The base pres- L 333