Correlation between fixed charge and capacitance peaks in silicon nanocrystal metal-insulator-semiconductor devices
Fixed charge in metal-insulator-semiconductor (MIS) devices featuring silicon (Si) nanocrystals (NCs) embedded in a silicon dioxide (SiO2) insulating layer has been examined. By means of capacitance-voltage (C-V) measurements, the density of net fixed positive oxide charge was found to decline over a 7 week period after device fabrication. Two capacitance peaks originally observed in the C-V curves were found to disappear over the same period. The disappearance of one of these peaks is attributable to reduced external inversion layer coupling. The second of these peaks disappears due to a reduced interface state response to the small signal excitation. An explanation for the decline in the small signal interface state response with the reduction in net fixed positive oxide charge is provided and supported by use of MIS tunnel diode modelling.