A very small amount of pre-deposited C on a Si substrate causes island formation after epitaxial growth of less than 2 monolayers Ge. These C-induced Ge dots can be as small as 10 nm in lateral size and 1 nm in height. Their areal density is1011 cm−2. Intense photoluminescence signal from these small Ge quantum dots is observed reaching a maximum for 2.1±0.3 monolayers of Ge. In the initial stages of island formation, the optical transition of the wetting layer is blue-shifted by strain compensation effects. We propose spatially indirect mechanisms of radiative recombination between electrons confined in the underlying wetting layer and holes confined in the Ge islands. ©1997 American Institute of Physics.