STM observations of three-dimensional Ge islands on Si(1 1 1) surfaces with different step orientations and step-bunching conditions

Ge growth on stepped Si(1 1 1) surfaces misoriented toward 〈1 1 2〉, 〈1 1 0〉 and 〈1 12 〉 was investigated with a scanning tunneling microscope (STM) on the same Si(1 1 1) substrate, where these different steps exist around the sidewall of a hole fabricated photolithographically. After high temperature (1200 °C) annealing for several minutes, the steps on the sidewall of a hole exhibit the threefold symmetry, which consists of debunching 〈1 1 2〉-type steps and heavy bunching 〈1 1 0〉 and 〈1 12 〉-type steps. After Ge deposition of up to three bilayers of Ge at 400 °C, the distribution of three-dimensional (3D) islands becomes selectable on the three types of stepped surfaces. The step-flow growth in the step band region decreases the critical thickness of the transition from two-dimensional to three-dimensional growth. The surface energy at the step bunch and Ge islands become more important than the strain energy, and selective growth of Ge islands is realized.