Influence of composition and substrate miscut on the evolution of {105}-terminated in-plane Si1−xGex quantum wires on Si(001)

Abstract

Isolated in-plane wires on Si(001) are promising nanostructures for quantum transport applications. They can be fabricated in a catalyst-free process by thermal annealing of self-organized Si1−xGex hut clusters. Here, we report on the influence of composition and small substrate miscuts on the unilateral wire growth during annealing at 570 °C. The addition of up to 20% of Si mainly affects the growth kinetics in the presence of energetically favorable sinks for diffusing Ge atoms, but does not significantly change the wire base width. For the investigated substrate miscuts of <0.12°, we find geometry-induced wire tapering, but no strong influence on the wire lengths. Miscuts <0.02° lead to almost perfect quantum wires terminated by virtually step-free {105} and {001} facets over lengths of several 100 nm. Generally, the investigated Si1−xGex wires are metastable: Annealing at ≥600 °C under otherwise identical conditions leads to the well-known coexistence of Si1−xGex pyramids and domes.