We report the epitaxial growth of Bi 2 Se 3 thin films on (0001) Al 2 O 3 substrates by hybrid physicalchemical vapor deposition (HPCVD). The HPCVD technique combines the thermal decomposition of trimethylbismuth with the thermal evaporation of Se and leads to a high Se partial pressure in the growth ambient. The Bi 2 Se 3 films are highly c-axis oriented on sapphire but contain planar defects including stacking faults and twin boundaries. Variable-temperature Hall-effect measurements demonstrate a carrier concentration of 5.8 Â 10 18 cm À3 and a mobility of 900 cm 2 /Vs at 4.2 K. These results demonstrate the potential of HPCVD for producing high quality Bi 2 Se 3 films for topological insulator studies. V C 2012 American Institute of Physics. [http://dx.

Recent electrical measurements have accessed transport in the topological surface state band of thin exfoliated samples of Bi2Se3 by removing the bulk n-type doping by contact with thin films of the molecular acceptor F4-TCNQ. Here we report on the film growth and interfacial electronic characterization of F4-TCNQ grown on Bi2Se3. Atomic force microscopy shows wetting layer formation followed by 3D island growth. X-ray photoelectron spectroscopy is consistent with this picture and also shows that charge transferred to the molecular layer is localized on nitrogen atoms. Ultraviolet photoelectron spectroscopy shows a work function increase and an upward shift of the valence band edge that suggest significant reduction in carrier density at the Bi2Se3 surface.

Intrinsic defects in Bi2Se3 topological insulators tend to produce a high carrier concentration and current leakage through the bulk material. Bi2Se3 thin films were grown by hybrid physical chemical vapor deposition on (0001) Al2O3 substrates with high Se vapor pressure to reduce the occurrence of Se vacancies as the main type of defect. Consequently, the carrier concentration was reduced to ∼5.75 × 1018 cm−3 comparable to reported carrier concentration in Bi2Se3 thin films. Magnetotransport measurements were performed on the films and the data were analyzed for weak anti-localization using the Hikami-Larkin-Nagaoka model. The estimated α and lϕ values showed good agreement with the symplectic case of 2-D transport of topological surface states in the quantum diffusion regime. The temperature and angular dependence of magnetoresistance indicate a large contribution of the 2-D surface carriers to overall transport properties of Bi2Se3 thin film.

The growth of thin Bi 2 Se 3 films on (0001) sapphire substrates by metalorganic chemical vapor deposition (MOCVD) was investigated. A two-heater configuration was employed to pre-crack the metalorganic sources upstream of the substrate while maintaining a low substrate temperature (<250 o C). Epitaxial Bi 2 Se 3 films with (006) x-ray rocking curve full-width-at-half-maximum values on the order of 160 arcsecs were obtained at growth rates of ~6 nm/min or lower while higher growth rates resulted in polycrystalline films. The background electron concentration of the films was found to depend strongly on the substrate temperature and Se/Bi inlet ratio. Bi 2 Se 3 films with a room temperature electron concentration of 6.7x10 19 cm -3 and mobility of 155 cm 2 /Vs were obtained at 200 o C with a Se/Bi ratio of 80. Higher substrate temperature and lower Se/Bi ratios resulted in an increase in electron concentration and corresponding reduction in mobility. The results demonstrate the potential of MOCVD for the growth of Bi 2 Se 3 and related materials for topological insulator studies.

a b s t r a c t Bi 2 Se 3 thin films were grown on c-plane sapphire substrates by hybrid physical-chemical vapor deposition (HPCVD) using trimethyl bismuth (TMBi) and Se pellets. A Se-rich environment is created by evaporating Se pellets in the vicinity of the substrate, which is used to suppress the formation of Se vacancies. The effects of pre-cracking temperature and substrate/Se temperature on the growth rate, structural and electrical properties of the Bi 2 Se 3 films were investigated. C-axis oriented films were obtained which show a reduction in the carrier concentration as pre-cracking temperature was increased from 290°C (1.6Â 10 19 cm À 3 ) to 350°C (8.4 Â 10 18 cm À 3 ). An additional reduction in carrier concentration (7.28 Â 10 18 cm À 3 ) was observed on increasing the substrate temperature from 200 to 260°C.