A method was described for obtaining high-quality strain–relaxed SiGe buffer layers on Si(001) substrates. In this method, the strain relaxation of the SiGe layer was performed by using a 2-step procedure. Firstly, a low-temperature-grown SiGe layer, whose surface was covered by a thin Si cap layer, was thermally annealed. At this stage, the strain was incompletely relaxed and an atomically flat surface could be realized. Then, a second SiGe layer was grown on the first layer to achieve further strain relaxation. Transmission electron microscopy has clearly revealed that dislocations were dispersively introduced into the first SiGe/Si substrate interface and thus no pile-up of dislocations occurred. The formation of a periodic undulation on the growth surface of the second SiGe layer was the key to inducing a drastic reduction in the threading dislocation density.

Reduction of Threading Dislocation Density in SiGe Layers on Si (001) using a Two-Step Strain–Relaxation Procedure. A.Sakai, K.Sugimoto, T.Yamamoto, M.Okada, H.Ikeda, Y.Yasuda, S.Zaima: Applied Physics Letters, 2001, 79[21], 3398-400