Hybrid Physical-Chemical Vapor Deposition of Bi$_{2}$Se$_{3}$ Thin films on Sapphire

High quality thin films of topological insulators continue to garner much interest. We report on the growth of highly-oriented thin films of Bi$_{2}$Se$_{3}$ on c-plane sapphire using hybrid physical-chemical vapor deposition (HPCVD). The HPCVD process utilizes the thermal decomposition of trimethyl bismuth (TMBi) and evaporation of elemental selenium in a hydrogen ambient to deposit Bi$_{2}$Se$_{3}$. Growth parameters including TMBi flow rate and decomposition temperature and selenium evaporation temperature were optimized, effectively changing the Bi:Se ratio, to produce high quality films. Glancing angle x- ray diffraction measurements revealed that the films were c-axis oriented on sapphire. Trigonal crystal planes were observed in atomic force microscopy images with an RMS surface roughness of 1.24 nm over an area of 2$\mu $mx2$\mu $m. Variable temperature Hall effect measurements were also carried out on films that were nominally 50-70 nm thick. Over the temperature range from 300K down to 4.2K, the carrier concentration remained constant at approximately 6x10$^{18 }$cm$^{-3}$ while the mobility increased from 480 cm$^{2}$/Vs to 900 cm$^{2}$/Vs. These results demonstrate that the HPCVD technique can be used to deposit Bi$_{2}$Se$_{3}$ films with structural and electrical properties comparable to films produced by molecular beam epitaxy.