Growth and structural study of the solid solution Si1−xGex (0 < x < 1)

Abstract

Single-crystal films of the Si_1−xGe_x (0 < x < 1) solid solution were grown on Si(1 1 1) substrates using liquid-phase epitaxy. The samples were grown from a tin melt solution at crystallization onset temperatures (To.c) → 1050°C, 980°C, 950°C, in a quartz reactor and a hydrogen atmosphere. The chemical composition, crystalline perfection, and single-crystallinity of the obtained films were studied, and the lattice parameter of the functional layer was determined to be a_Si1−xGex = 5.6414 ± 0.0004Å. Excellent sample surface smoothness was demonstrated: the average roughness height of the resulting films was 1.66 nm, and the pit depth was 1.18 nm. A method for controlling the dislocation level based on varying the film composition was proposed and tested. Thus, with a change in the silicon content in the film, the dislocation density changed from N_D ∼ 8·10⁵ cm⁻² (x = 0.5) to N_D ∼ 2·10⁴ cm⁻² (x = 1). This phenomenon was explained by the influence of mechanical stresses arising in the grown film. It was shown that the variegated chemical composition of the solid solution smooths out the difference in lattice parameters and CTE between the epilayers. This value is always smaller than the critical thickness of the pseudomorphic layer, which is estimated at d_f = 3.31 nm. It has been shown theoretically and experimentally that the deformation stress reaches its maximum (${\sigma }_{{\delta }_{(x=0.5)}}$ = 4.5946GPa) in the intermediate concentration region of Si_0,5Ge_0,5 (x = 0.5). Despite the high stress levels, the films obtained in this manner remain epitaxial. Maintaining the epitaxial state is largely facilitated by the fact that part of the strain stress energy (Δ = 0.0332 J/m2) is relaxed through the formation of dislocations. Film delamination was studied and the Griffith boundary stresses were determined, which for Si_1−xGe_x at x  = 0.36 are σ_g = 2.6773GPa. The electrophysical parameters of the films at a temperature of 300 K were determined: ρ = 0.5–5 Ohm∙cm, µ_n = 300 cm²/V∙s, n= (5–7) ∙ 10¹⁸ cm⁻³, and the prospects for applied use of the obtained films were assessed.