Evolution of Ge/Si(001) islands upon oxidation and water etching

Surface germanium oxide is often ignored in the ex situ characterization of Ge coherent islands grown on Si substrates. Therefore, the effects of the native oxide have to be justified. We thus intentionally oxidize the Ge coherent islands in air and ozone, strip the oxide layer by water, and assess the effects of native GeOx oxide layer on ex situ shape and strain measurements. We estimate that the thickness of Ge consumed due to its oxidation in air is similar to0.4 nm in domes and less than 0.4 nm in pyramids. This native oxide on the Ge islands has negligible effect on the island shape and strain measurements. Upon etching in water, domes continuously change their shape to lower aspect ratio. Thus, island aspect ratio can be tailored in a controllable fashion by water etching due to the different oxidation rate between the base and top of the island. The dependence of strain relaxation in a coherent island on aspect ratio is compared with the theoretical calculations. (C) 2002 Elsevier Science B.V. All rights reserved.