Insitu Observation Of Growth-Rate Enhancement During Gas Source Molecular-Beam Epitaxy Of Si1-Xgex Alloys On Si(100) Surfaces

Using reflection-high-energy-electron-diffraction intensity oscillations the growth rate of Si1-xGex alloys at various compositions and different growth temperatures has been studied in situ. It was found that the growth rate shows a strong dependence on GeH4 flux at low temperatures (T < 600-degrees-C), while at high temperatures (T > 600-degrees-C) the growth rate is nearly independent of the GeH4 flux but proportional to the incident Si2H6 beam flux. In addition to the enhanced growth rate, a lower activation energy is observed in the low temperature region when compared to Si homoepitaxy from Si2H6. This suggests that surface germanium atoms act as good sites for hydrogen removal which is known to inhibit Si growth from hydride sources at low temperatures. Above 600-degrees-C, however, surface hydrogen is desorbed thermally and the addition of GeH4 has little effect on the growth rate.