HETEROEPITAXY OF GAP ON SI(100)

In this article, we analyze the kinetics of heteroepitaxial growth of GaP on Si(100) by pulsed chemical beam epitaxy on the basis of results obtained by real-time optical process monitoring. In view of the larg e barrier to epitaxial growth on oxygen or carbon contaminated silicon surface elements and the low stacking fault energy for CaP, residual contamination of the silicon surface contributes to defect formation i n the initial phase of GaP heteroepitaxy on Si, and requires special m easures, such as surface structuring, to Limit the propagation of defe cts into the epitaxial film. The control of the supersaturation during the first 10-20 s of film formation is essential for the quality of s ubsequent epitaxial growth and is limited to a narrow process window b etween three-dimensional nucleation and overgrowth at low Ga supersatu ration and gallium-cluster formation at high Ga supersaturation. Stead y state heteroepitaxial growth is described by a four-layer stack subs trate/epilayer/surface reaction layer (SRL)/ambient and, depending of the source vapor flux, allows for more than monolayer coverage. Under this special condition of low-temperature CBE, the kinetics of chemica l reactions in the SRL is composed of homogeneous reactions creating/c onsuming intermediates that participate in surface reactions including the incorporation of Ga and P atoms into the epitaxial film. For the homogeneous part of the surface kinetics the dipole approximation prov ides an adequate correlation of the changes in the dielectric function of the SRL to the activities of randomly distributed reactants and pr oducts. No adequate correlation of the dielectric function exists to t he concentrations of strongly bonded surface atoms and surface molecul es. Therefore, quantitative assessments of the heterogeneous kinetics on the crystal surface cannot use real-time optical monitoring as a re liable basis. (C) 1996 American Vacuum Society.