Interface and border trap relaxation in Si–SiO2 structures with Ge nanocrystals examined by transient capacitance spectroscopy

The formation of interface and border states in metal–oxide–semiconductor structures associated with the generation of embedded germanium nanocrystals in 20 nm SiO2-layers by means of ion implantation and a subsequent annealing was examined. Deep level transient spectroscopy and related time-domain techniques were applied in order to study the charge trapping and emission at the Si–SiO2 interface. A significant dependence of the interface state density Dit on the conditions of the cluster generation was found. Any Ge-implanted sample features a pronounced level at about 0.31 eV above the valence band edge and a concentration above 1013 cm−2 eV−1, likely related to a Pb-center. A systematic variation of the filling pulse parameters was utilized in order to separate the response of fast and slow states, and to substantiate the existence of border traps located in the vicinity of the Si–SiO2 interface. The role of interface and border traps for the relaxation of the trapped charge in the nanocrystals is illustrated.