Effect of film growth rate and thickness on properties of Ge/GaAs(100) thin films

We present a profound effect of film growth rate and thickness on the electrical properties, intrinsic stresses and surface/interface morphology of thin (1 nm to 250 nm) Ge films grown on GaAs(100). The films studied in this work are epitaxially grown and have single crystal structure. The film-substrate interfaces are coherent, without misfit dislocations. At high deposition rates, the film surface is smooth and does not depend on the film thickness in contrast to low growth rate films that show pronounce surface roughness as the film thickness increases. The intrinsic stresses in the films decreased with lower deposition rate. Moreover, the Ge films obtained at high deposition rates are n-type, have low resistance and a high concentration of free charge carriers. The weak temperature dependence of conductivity of high deposition rate specimens indicates that these films are heavily doped degenerate semiconductors. The films prepared with low deposition rates are p-type and highly resistant, with a low concentration of free charge carriers, and exhibit thermally activated conductivity of percolation-type. (C) 2013 Elsevier B.V. All rights reserved.