Blanket and selective Ge growth on Si was investigated using reduced pressure chemical vapour deposition. To reduce the threading dislocation density at low thickness, Ge deposition with cyclic annealing followed by HCl etching was performed. In the case of blanket Ge deposition, a threading dislocation density of 1.3 x 106/cm2 was obtained, when the Ge layer was etched back from 4.5μm thickness to 1.8μm. The threading dislocation density was not increased relative to the situation before etching. The root mean square of roughness of the 1.8μm thick Ge was about 0.46nm, which was of the same level as before HCl etching. Further etching showed increased surface roughness caused by non-uniform strain distribution near the interface due to misfit dislocations and threading dislocations. The threading dislocation density also became higher because the etch front of Ge reaches areas with high dislocation density near the interface. In the case of selective Ge growth, a slightly lower threading dislocation density was observed in smaller windows caused by a weak pattern size dependence on Ge thickness. A significant decrease of threading dislocation density of selectively grown Ge was also observed by increasing the Ge thickness. An about 10 times lower threading dislocation density at the same Ge thickness was demonstrated by applying a combination of deposition and etching processes during selective Ge growth.

Low Threading Dislocation Ge on Si by Combining Deposition and Etching. Y.Yamamoto, G.Kozlowski, P.Zaumseil, B.Tillack: Thin Solid Films, 2012, 520[8], 3216-21