GERMANIUM SEGREGATION INDUCED RECONSTRUCTION OF SIGE LAYERS DEPOSITED ON SI(100)

The surface structure of SiGe layers deposited on Si(100) has been studied by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). AES spectra reveal a strong germanium segregation. The 2 x 1 surface reconstruction of Si(100) observed by LEED is changed into a 2 x n (n > 8) structure on deposition of SiGe layers. Corresponding STM pictures reveal a surface built up from terraces with alternately oriented dimer rows. After n - 1 subsequent dimers, however, one dimer is missing. Those missing dimers form lines which give rise to the 2 x n LEED pattern. The density of missing dimers depends on the germanium content and on the layer thickness, The evaluation of the LEED intensities can explain the structure by a small expansion of the topmost SiGe layer enriched by germanium.