Characterization of strain relaxation behavior in Si_1−xGe_x epitaxial layers by dry oxidation

We fabricated fully strained Si_0.77Ge_0.23 epitaxial layers on Si substrates and investigated their strain relaxation behaviors under dry oxidation and the effect of oxidation temperatures and times. After the oxidation process, a Ge-rich layer was formed between the oxide and the remaining Si_0.77Ge_0.23 layer. Using reciprocal space mapping measurements, we confirmed that the strain of the Si_0.77Ge_0.23 layers was efficiently relaxed after oxidation, with a maximum relaxation value of ~ 70% after oxidation at 850 °C for 120 min. The surface of Si_0.77Ge_0.23 layer after strain relaxation by dry oxidation was smoother than a thick Si_0.77Ge_0.23 layer, which achieved a similar strain relaxation value by increasing the film thickness. Additionally, N2 annealing was performed in order to compare its effect on the relaxation compared to dry oxidation and to identify relaxation mechanisms, other than the thermally driven ones, occurring during dry oxidation.