Formation and optical properties of carbon-induced Ge dots

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 snail as 10 nm in lateral size and 1 to 2 nm in height. The area density is about 1 x 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 Si1-xGex/Si1-yCy 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. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.