Morphological evolution during Ge/Si(100) heteroepitaxy

We have investigated the morphological evolution of islanded Ge/Si(100) samples formed by > 3 monolayer (ML) Ge deposition. Ge was deposited onto Si(100) surfaces cleaned by flash desorption of the native oxide at rates near 1/2 ML per minute. Growths were performed in an ultra-high vacuum system with a base pressure of < 10 ^-9 Torr. Substrate temperature during growth was 500 °C. Post-deposition processing ranged from no additional treatment to 1 hour at 560 °C anneals. Samples removed from the growth chamber were processed using standard transmission electron microscopy (TEM) specimen preparation techniques and characterized using plan-view TEM. Micrographs were computer analyzed to generate island size distributions (histograms of island size). These size distributions fall into general classes. First, samples with only coherent Ge islands exhibit relatively narrow size distributions. Secondly samples with both coherent and incoherent islands presented bi-modal size distributions with coherent islands populating the smaller radii. These results will be discussed in the context of a model which includes elastic as well as surface and interface energies as driving forces for ripening.