Thin, relaxed Si_1−xGe_x virtual substrates on Si grown using C-doped Ge buffers

Ultrathin C-doped Ge (Ge:C) buffers are used as effective buffer layers to grow thin and smooth Si_1−xGe_x relaxed virtual substrates on Si over a wide range of Ge content (x = 0.23, 0.38, 0.50, 0.65, 1) by ultrahigh vacuum chemical vapor deposition. High degree of relaxation (≥90%) in thin Si_1−xGe_x films (∼50 nm thick) is demonstrated using this approach without additional annealing. Raman data suggest that the Ge:C buffers are still under compressive stress with the subsequent Si_1−xGe_x layer growth. A low threading dislocation density of the order of ∼6 × 10⁴cm⁻² is obtained from the relaxed 500-nm Si_0.77Ge_0.23 film grown using this method.