Size-dependent charge storage in amorphous silicon quantum dots embedded in silicon nitride

Size-dependent charge storage was observed in metal–insulator–semiconductor structures containing amorphous Si quantum dots $\mathrm{(a-}\mathrm{Si}$ QDs) grown by plasma-enhanced chemical vapor deposition. For $\mathrm{a-}\mathrm{Si}$ QDs as large as 2 nm in diameter, one electron or one hole was stored in each $\mathrm{a-}\mathrm{Si}$ QD. For small-sized $\mathrm{a-}\mathrm{Si}$ QDs of 1.4 nm in diameter, however, the width of capacitance–voltage hysteresis was decreased, indicating that the charge density in the $\mathrm{a-}\mathrm{Si}$ QDs was reduced. This can be attributed to the lowered tunneling barrier in the small-sized $\mathrm{a-}\mathrm{Si}$ QDs resulting from a large quantum confinement effect. Long-term charge storage was observed in the fully charged $\mathrm{a-}\mathrm{Si}$ QDs; this is attributed to a suppression of the discharge process by electrostatic repulsion among the charged dots.