Nominal Ge islands were grown by a molecular beam epitaxy technique on a Si(001) substrate. Island positions and shapes were measured by atomic force microscopy. Two types of islands with different sizes and shapes are present. The Si concentration distribution inside the islands was measured by Raman imaging technique with a 0.4 μm resolution, and was found to vary between 10% and 30% in large islands and be 10% in smaller islands. © 1998 American Institute of Physics.