Electron and hole charging effect of nanocrystalline silicon in double-oxide barrier structure

The nanocrystalline silicon (nc-Si) based double-oxide barriers structure on p-Si substrates (SiO2/nc-Si/SiO2/p-Si) was fabricated by layer-by-layer technique and in situ plasma oxidation in a plasma enhanced chemical vapor deposition (PECVD) system. The nc-Si layer with the thickness of 8 nm was deposited on the tunneling oxide (2 nm) and then oxidized to form the gate oxide (5 nm). By using frequency dependent capacitance spectroscopy, the tunneling effects of holes and electrons were investigated. In capacitance curves measured at low frequency three peaks were observed, which could be attributed to the resonant tunneling of electrons into discrete energy levels of nc-Si and exhibit quantum confinement and Coulomb blockade effects. Quantitatively, we estimated the coulomb charging energy and energy spacing between ground and first excited energy level of nc-Si from ΔVG to be about 57 and 257 meV, respectively, which agree well with the theoretical calculations.