Effect of bismuth on structural and electrical properties of InAs films grown on GaAs substrates by MBE

Abstract

InAs films were grown on GaAs substrates by molecular beam epitaxy (MBE) without or with different Bi fluxes. The effect of Bi on the structural and electrical properties of the InAs films was studied. Atomic Force Microscopy (AFM) measurement showed clear surface steps in all samples, indicating an over-flow growth mode. A more uniform distribution and narrower spacing of the surface steps were observed with increased Bi fluxes. Small area AFM scans showed reduced surface roughness with increased Bi fluxes. Whereas from large area scans, reduced surface roughness was only observed in samples grown under low Bi fluxes, and a deteriorated surface was obtained in the sample grown under the highest Bi flux. Bi was not compositionally incorporated to the InAs films confirmed by X-ray diffraction (XRD) and Second Ion Mass Spectroscopy (SIMS) measurements. The electron mobility of the InAs films, measured at room temperature, decreased monotonically with increased Bi fluxes. This is correlated to the Transmission Electron Microscopy (TEM) results in which increased threading dislocation (TD) densities were shown with increased Bi fluxes. Therefore, Bi-mediated growth deteriorates the electron mobility of the MBE-grown InAs films, whereas smoother surface can be obtained by applying low Bi fluxes. Possible mechanisms were proposed to explain these phenomena.