Origin of charge trapping in germanium nanocrystal embedded SiO2 system: Role of interfacial traps?

Abstract

Wet thermal oxidations of polycrystalline Si0.54Ge0.46 films at 600 °C for 30 and 50 min were carried out. A stable mixed oxide was obtained for films that were oxidized for 50 min. For film oxidized for 30 min, however, a mixed oxide with Ge nanocrystallites embedded in the oxide matrix was obtained. A trilayer gate stack structure that consisted of tunnel oxide/oxidized polycrystalline Si0.54Ge0.46/rf sputtered SiO2 layers was fabricated. We found that with a 30 min oxidized middle layer, annealing the structure in N2 ambient results in the formation of germanium nanocrystals and the annealed structure exhibits memory effect. For a trilayer structure with middle layer oxidized for 50 min, annealing in N2 showed no nanocrystal formation and also no memory effect. Annealing the structures with 30 or 50 min oxidized middle layer in forming gas ambient resulted in nanocrystals embedded in the oxide matrix but no memory effect. This suggests that the charge storage mechanism for the trilayer structure is closely related to the interfacial traps of the nanocrystals.