Capacitance-voltage characterization of Ge-nanocrystal-embedded MOS capacitors with a capping Al₂O₃ layer

Capacitance versus voltage (C-V) curves of Ge-nanocrystal (NC)-embedded MOS capacitors with and without a single capping Al₂O₃ layer are characterized in this work. C-V curves of the Ge-NC-embedded MOS capacitor with the Al₂O₃ layer are counterclockwise in the voltage sweeps, which indicates the presence of charge storages in the Ge NCs by the tunnelling of charge carriers between the Si substrate and the Ge NCs. In contrast, clockwise hysteresis of the C-V curves and leftward shifts of the flat band voltages are observed for the embedded MOS capacitor without the Al ₂O₃ layer. It is suggested here that the observed characteristics of the C-V curves are due to the charge trapping at oxygen vacancies within a SiO₂ layer. In addition, the illumination of the white light enhances the lower capacitance part of the C-V hysteresis. The origin for the enhancement is discussed in this paper.