Microstructural Characterization And Analysis In Heteroepitaxial Films

High-quality heterostructures are the key structural components to ensure high performance of semiconductor devices and have always been challenging in epitaxial growths.The difficulty is originated from the mismatch of properties such as lattice constant,structural symmetry and thermal expansion coefficient between the epitaxial film and the substrate.Microscopic structural characterization can help us to obtain important information inside the material,including defects and stress distribution,etc,and to further guide the growth condition optimization and structural design.Moreover,phase and phase transition in the heterostructure films is also of great interest.Understanding different phases and their distributions in the heterogeneous structure is the key to growth study phase separation.In this paper,we chose two heteroepitaxial material systems grown by molecular beam epitaxy(MBE),which are Si1-xGex/Si system with a large mismatch and metastable ?-Sn on InSb and characterized them by transmission electron microscopy(TEM).The defects and strain relaxation mechanism in the Si1-xGex/Si system and the metastable phase and phase separation in the ?-Sn/InSb structures were studied,respectively.The key research results are summarized as follows:(1)We have found that in the epitaxial Si1-xGex films grown on Si,as x increases,threading dislocation density increases and the stacking fault length is found to be inversely proportional to the Ge content.(2)We have also found a multilayer structure in the Si1-xGex film with local shearing,but the tilting angle was about 1°.We believe that local shearing helps the strain relaxation and thus reduces dislocations density.The measurement of threading dislocation density of the Ge films(?104/cm2)also supports this hypothesis.The mechanism of low temperature epitaxial growth of Si1-xGex films and the non-typical strain relaxation mechanism are presented.(3)The TEM sample of the metastable ?-Sn film was successfully prepared by ion milling under liquid nitrogen conditions,and the original a phase in the sample was retained.(4)The epitaxial Sn film was characterized by SEM and EBSD to identify the phase and obtain the distribution of a phase and ? phase in the sample.(5)High resolution TEM images of the ?-Sn/InSb interface and atomic resolution images of ? phase and ? phase were obtained by cross-section TEM.And a model of how the two phases coexistence was proposed.