Fabrication and characterisation of locally grown SiGe wires and dots

Abstract

Molecular beam epitaxy has been used to fabricate SiGe quantum wires and dots with lateral dimensions as small as 200 nm on 3in Si (100) substrates through ultrahigh vacuum compatible microshadow masks. The shadow mask consists of a low pressure chemical vapour deposited Si nitride layer (100 nm) on top of a thermal Si dioxide layer (1 μm). Patterning of the microshadow mask has been carried out by electron beam lithography in combination with a reactive ion etching technique using a three level poly(methyl methacrylate)–Ti–AZ 5206 resist system and wet etching of the Si dioxide spacer. Scanning electron microscopy and transmission electron microscopy reveal quantum wells of high crystalline quality, completely embedded in Si by the applied growth technique. Photoluminescence measurements show clear excitonic emission from the fabricated SiGe structures. On reducing the mesa sizes from 2 μm to 200 nm, a pronounced blue shift of the SiGe related signals was observed. Obviously for these large widths, lateral quantum confinement cannot account for such strong shifts. This phenomenon is discussed considering lateral diffusion effects of Ge on the surface during the molecular beam epitaxy deposition process.

MST/3255