Study of Si/Ge Strain-Controlled Atomic-Laver Super-Lattices

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Hetero atomic-layer epitaxy (ALE) methods have been developed for both Si on the Ge substrate and Ge on the Si substrate. And the ALE-growth characteristics were clarified by using various surface-sensitive evaluation methods. Base on these results, strain-controlled Si/Ge atomic layer super-lattices have been fabricated. The major results are listed below.1. By alternative exposure of DCS (SiH2Cl2) and atomic hydrogen, AH, a Si homo-ALE procedure has been established with an ideal 1ML/cycle growth rate on both (100) and (111) surfaces. An ALE-window was from 530oC to 610oC.Microscopic growth kinetics has been investigated by using surface morphology change, and the extremely flat grown surface with increased surface roughness of less than 0.1A was obtained under the optimum ALE conditions.2. By alternating exposure of DMG (GeH2(CH3)2) and AH, Ge-ALE procedure has been established with the 1ML/cycle growth rate over a wide temperature window from 430oC to 520oC.But due to large amount of residual C in the grown film, the grown surface flatness was deteriorated for temperatures more than 445oC.GeH2Cl2 seems the desired source material to the wider temperature window for the flat surface.3. 1ML-thick adsorption of Si has been done on the Ge surface by using SiH4. The atomically abrupt Si/Ge hetero interface has been fabricated by carrying out the Si ALE on this 1ML-thick Ge on Si structure. This atomically abrupt hetero structure was thermally stable up to 550oC..4. By alternating exposure of GTC (GeCl4) on the Si surface, 1ML-thick Ge layer was formed. This structure was concluded to be an ideal 1MLGe/Si hetero structure without clustering and intermixing. Atomically abrupt Ge/Si hetero interface has been fabricated by successive home ALE of Ge.5. By using these hetero ALE methods, Si7/Ge3 atomic-layer super-lattices with internal stain has been fabricated and their microscopically fine structures were observed by a transmission electron microscope.