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 large 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 in the initial phase of GaP heteroepitaxy on Si, and requires special measures, such as surface structuring, to Limit the propagation of defects into the epitaxial film. The control of the supersaturation during the first 10-20 s of film formation is essential for the quality of subsequent epitaxial growth and is limited to a narrow process window between three-dimensional nucleation and overgrowth at low Ga supersaturation and gallium-cluster formation at high Ga supersaturation. Steady state heteroepitaxial growth is described by a four-layer stack substrate/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 chemical reactions in the SRL is composed of homogeneous reactions creating/consuming 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 provides an adequate correlation of the changes in the dielectric function of the SRL to the activities of randomly distributed reactants and products. No adequate correlation of the dielectric function exists to the concentrations of strongly bonded surface atoms and surface molecules. Therefore, quantitative assessments of the heterogeneous kinetics on the crystal surface cannot use real-time optical monitoring as a reliable basis. (C) 1996 American Vacuum Society.