MBE growth of Ge quantum dot structures in oxide windows

Abstract

Abstract. The implementation of Quantum Dots (QDs) in devices allows novel electronic and opto-electronic functions. Strain driven Stranski-Krastanov growth mode enables the formation of nanometric islands (on wetting layer) whose density and geometry depend on growth conditions (temperature, rate) and surface structure (cleaning). The island positions are random. However, they can be influenced by surface patterning. In this work, the MBE growth of self-organized Ge QD structures in oxide windows is investigated. The studied Ge QD structures are composed by either a single Ge layer directly grown on a Si substrate, or double layer formed by a Ge QD layer on top of a Si buffer layer. Different surface preparation (dry etching with and without anisotropic wet etching) and cleaning (HF dip or RCA cleaning) schemes have been used. It is found that the cleaning and the Si buffer layer growth have strong influence on island nucleation. Preferred nucleation at the window edge and/or nucleation at the window center is observed under certain conditions. Interestingly, negligible influence (this is needed for most device works) is found only if Ge is grown directly on the RCA cleaned window.

Recent developments in Ge dots grown on pit‐patterned surfaces

“…Control over the nucleation sites can also be achieved by manipulating the surface topography prior to Ge deposition, either by depositing and structuring a mask layer on the surface or by introducing elevations or depressions directly in the Si substrate. Oxide windows 10, 11 or metal masks 12 have been successfully used for directed Ge dot growth. Ge dots can be grown on elevated Si stripes or mesas that are fabricated by selective epitaxial growth of Si in windows in a prepatterned SiO 2 mask 13.…”