Roczen, M.; Schade, M.; Malguth, E.; Callsen, G.; Barthel, T.; Gref, O.; Töfflinger, J.A.; Schöpke, A.; Schmidt, M.; Leipner, H.S.; Ruske, F.; Phillips, M.R.; Hoffmann, A.; Korte, L.; Rech, B.: Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications. Applied Physics A 108 (2012), p. 719-726
10.1007/s00339-012-6956-9
Abstract:
The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultra-thin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultra-high vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700 °C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO2 shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO2 interface with a low amount of suboxides. A minority charge carrier lifetime of 18 µs inside of the nanodots is determined.