Effects of Si Spacer-Layer on the Structure of Ge/Si Quantum Dots Bilayers Grown by Ion Beam Sputtering

Abstract

A series of double-layer Ge/Si quantum dots are prepared by ion beam sputtering deposition (IBSD) on Si (100) substrates. The influences of deposition temperature and thickness of Si spacer-layer on the microstructure of double-layer Ge/Si quantum dots were characterized by using Atomic force microscopy (AFM) and Raman spectra technique. The results indicate that the density of the second layer islands firstly increases and then decreases with increasing the growth temperature of Si spacer-layers. In addition, increasing the thickness of Si spacer-layer, the islands merger phenomenon disappears. When the deposition thickness is larger than 40 nm, the islands on the upper-layer show the same features with the buried islands. The mechanism of three-factor-interactions of nanoislands is proposed to explain these phenomena, and our results can be used as a guidance to obtain optimum IBSD growth process for Ge/Si quantum-dot superlattices.