Formation and optical properties of carbon-induced Ge dots

Abstract

A small portion of a monolayer of pre-deposited carbon on Si (100) causes Ge island formation after epitaxial growth of less than two monolayers (ML) Ge. The epitaxial growth is done in a solid source MBE system. The carbon-induced Ge quantum dots can be as small as 10 nm in lateral size and 1 to 2 nm in height. The area density is about 1×10 11 cm −2. Pure Ge on Si forms large dots of about 100 nm in lateral size. Compared to Si/SiGe quantum wells and neighboring Si 1− x Ge x /Si 1− y C y quantum wells we observe very intensive photoluminescence (PL) signal from such small Ge dots. Varying the C and Ge deposition reveals a distinct PL intensity maximum for 0.2 ML C followed by about 2.2 ML Ge. We propose a spatially indirect radiative recombination mechanism. Vertical stacking of the C-induced Ge dots results in strongly increased PL intensity and red shifted transition energy.