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Distributions of both electron traps and hole traps in metal/oxide/nitride/oxide/silicon (MONOS) structures were studied. These trap distributions were analyzed by using a combination of an avalanche-injection method and capacitance-voltage measurement. The thicknesses of the nitride layers in the MONOS capacitors were varied. It was found that electron traps are mainly located at both the top and bottom oxide/nitride interfaces, whereas hole traps are located at the interfaces as well as in the nitride bulk. This analysis clarified that electron-trap capability decreases anomalously in the range of nitride thickness of less than 4 nm. Moreover, the effective activation energy of electron emission also decreases at nitride thickness less than around 5 nm. These decreases are considered to be accounted for by detrapping due to the Coulomb repulsion between electrons at both interfaces and electron trapping in the interfacial transition layers.
Date of Publication: Feb. 2013