Dynamics and Kinetics of Si/Si_(_1-_x_)Ge_(_x_) MBE studies by reflectance spectroscopy

Reflectance anisotropy (RA) and reflection high energy electron diffraction (RHEED) have been used simultaneously to study the growth of Si and Si_(_1_-_x_)Ge_x on Si(001) surfaces by gas source molecular beam epitaxy (GSMBE). Dynamic oscillatory changes in the RA response have been investigated and attributed to periodic changes in the domain coverage of the (2x1) and (1x2) reconstructions. These measurements demonstrate that RA gives a more direct measure of domain coverage variations on the Si(001) surface than RHEED, which may include ordering and multiple scattering effects. RA was used to investigate domain coverage variations as a function of substrate temperature and as a result of growth interruption. The temperature dependence of the change in the RA response is interpreted as a growth mode change at higher temperatures and a change in the electronic configuration of the surface dimers due to chemisorbed hydrogen at low substrate temperatures. The change in the RA response during deposition of Si_(_1_-_x_)Ge_x are also investigated as a function of Ge concentration. Reflectance anisotropy spectroscopy (RAS) has been used to monitor changes in the surface hydrogen coverage during growth and the difference between the RA spectra obtained before and after hydrogen exposure has been used to quantify monohydride coverage as a function of substrate temperature, flux and hydrogen source. The kinetics of Si growth have also been investigated and isothermal hydrogen desorption measurements have been made. Interruption of the disilane supply leads to a change in the RA response which can be attributed to the associative desorption of molecular hydrogen. Subsequent to the interruption of growth, the hydrogen coverage is found to vary linearly with time, changing to an exponential like dependence as the hydrogen coverage approaches zero. This zeroth order coverage dependence of hydrogen desorption is attributed to a desorption pathway incorporating a saturated and localised precursor state in which the diffusion/migration of surface hydrogen is not the rate limiting step. (author)Available from British Library Document Supply Centre-DSC:DXN033363 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo