Thin, Relaxed Si1−xGex 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 Si1−xGex 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 Si1−xGex 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 Si1−xGex layer growth. A low threading dislocation density of the order of ∼6 × 104 cm−2 is obtained from the relaxed 500-nm Si0.77Ge0.23 film grown using this method.