We report an experimental study of the optical properties of island layers resulting from molecular beam epitaxial deposition of Ge on Si(111) substrates. The combination of electroreflectance spectroscopy of theE1transition and Raman scattering allows us to separately determine the strain and composition of the islands. For deposition at 500 °C a deposited layer of 1.36 nm of Ge assembles into 80 nm diameter islands 11 nm thick. The average Si impurity content in the islands is 2.5&percent; while the average in-plane strain is 0.5&percent;. Both strain and Si impurity content in islands decrease with increasing Ge deposition. ©1997 American Institute of Physics.