Growth and microstructure of Si/CaF2/Si(111) heterostructures

The microstructure of the MBE-grown Si/CaF2/Si (111) heterostructures is st udied by high resolution transmission electron microscopy (HRTEM). Two dist inct interface structure models have been identified from comparison with i mage simulations. In the first model interfacial Ca atoms bond to T sites. In the second model Ca bonds to T-4 sites. No one proposed model alone can describe the microstructure. Imaging conditions have been identified by ana lysis of simulated images which enable unambiguous discrimination between a lternative models. No differences have been found between the microstructur es of the top and bottom interfaces. It has been shown by simulations that intermixing effects at the interface can be detected. However, such effects have not been observed experimentally Stacking faults and twins have been observed in the top Si layer. Sensitivity of the microstructure to 200 kV e lectron irradiation is quantified to determine the electron dose budget for unobtrusive HRTEM observation. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.