Electron diffraction methods for the analysis of silicon carbide surfaces and the controlledgrowth of polytype heterostructures

Abstract

The growth of different silicon carbide (SiC) polytypes on each other is possible bycontrol of the surface structure and the appropriate thermodynamic parameters.Special ultrahigh vacuum conditions, like those used in solid source molecular beamepitaxy, allow the determination of the species on the surface and also the in situcharacterization of the growing polytype by electron diffraction methods. Thesurface reconstruction which favours the growth of a certain polytype can becontrolled by reflection high energy electron diffraction. For a non-destructivedetermination of the polytype of a grown thin SiC film, methods like x-ray photoelectrondiffraction (XPD) and electron channelling can be used. The interaction length ofelectrons near 1 keV kinetic energy is in the range of 1 nm and therefore sensitiveto the stacking sequence of the most common SiC polytypes 3C, 4H, 6H withc-axis dimensions between 0.75 and 1.5 nm. To prepare polytype heterostructures like 4H/3C/4H or6H/3C/6H, untwinned 3C SiC films without double-positioning boundaries have to be grown. On-axisα-SiC substrates with uniform surface stacking termination are a prerequisite for this. Suchsurfaces can be prepared using high temperature hydrogen etching, sublimation etching orstep-flow growth. These equally terminated crystals with threefold surface symmetry areparticularly suitable for detailed studies of the atomic-geometric structure and theirchanges during growth or after certain treatments. Results of surface-sensitivecharacterization methods like scanning tunnelling microscopy, XPD and low energyelectron diffraction are presented.