We found out and studied a profound effect of film growth rate on the electrical properties, intrinsic
stresses and surface morphology of thin Ge films grown on GaAs(100). This effect is essential and has to be
accounted for when developing and producing devices based on the Ge/GaAs heterostructure. All the Ge
films under investigation were single-crystalline and epitaxially-grown on the GaAs(100) substrates. However,
the transport phenomena in Ge films grown at low and high deposition rate differed drastically.
Those obtained at low deposition rate were p-type and high resistant. They had a low concentration of free
charge carriers and thermally activated conductivity, which is characteristic of heavily doped and strongly
(in the limiting case, fully) compensated semiconductors. Although such films were single-crystalline, their
conductivity was percolation-type. The Ge films obtained at high deposition rate were n-type and low resistant.
They had high concentration of free charge carriers. The temperature dependence of conductivity
in such films was weak or practically absent, which is characteristic of degenerate heavily doped semiconductors.
Besides, the surface morphology cardinally differed for films obtained at low and high deposition
rate. At low film growth rates, surfaces with developed relief were observed whose valleys and ridges
formed grains of irregular shape with pronounced substructure. As the film thickness grew, the surface relief
became essentially pronounced. At rather high film deposition rates, contrary to the above, the Ge film
surface was fine-grained and smooth; the surface relief practically did not depend on the film thickness. As
the deposition rate went down, the intrinsic stresses in films essentially decreased. The results obtained
were analyzed from the viewpoint of formation of compositional and morphological inhomogeneities, and
fluctuations of electrostatic potential at low growth rates. Such potential fluctuations modulate Ge energy
bands leading to appearance of potential relief and deep tails of density of states in the Ge bandgap.
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