SI1-XGEX ALLOY GROWTH ON SI(111) SURFACES FROM GASEOUS HYDRIDE SOURCES

Reflection-high-energy-electron-diffraction (RHEED) has been used to m onitor surface structure and growth rate during Si1-xGex heteroepitaxi al growth from Si2H6 and GeH4 on Si(111) surfaces. Growth followed by low-temperature annealing results in a mixed 5 x 5 + 7 x 7 reconstruct ion which may be due to low adatom mobility producing local compositio nal gradients which influence 2D nucleation. Upon annealing, the conce ntration gradient is removed and the reconstruction is determined by t he strain, becoming a homogeneous 5 x 5 or 7 x 7 dependent on Ge surfa ce composition. The growth rate is found to decrease dramatically duri ng low-temperature growth at the Si/Si1-xGex interface which is in con trast to findings on the (100) surface at these temperatures. A number of factors are likely to influence this, including a lower dissociati ve reaction probability due to the presence of surface Ge, and reduced adatom mobility which hinders hydrogen desorption processes. Finally, the observed decrease in growth Tate occurs over a number of layers, and is discussed in terms of Ge surface segregation.