Electronic Properties of Nanocrystalline-Si Embedded in Asymmetric Ultrathin SiO₂ by In-Situ Fabrication Technique

Structures of nanocrystalline-Si (nc-Si) sandwiched between two asymmetric ultrathin SiO₂ layers were fabricated. The nc-Si (dot density of 10¹¹cm^-2) was formed by decomposition of hydrogen-diluted silane and the ultrathin SiO₂ layers (about 2nm) were prepared by plasma oxidation at a lower temperature (250°C). The whole fabrication processes were completed in situ in a plasma-enhanced chemical vapour deposition system. By using the capacitance--voltage (C--V) and conductance--voltage (G--V) spectroscopy, we studied the electronic properties of the annealed samples. The experimental results show that there are distinct capacitance peaks and conductance plateau or peaks for annealed samples at room temperature, which can be explained by direct tunnelling of electrons into the nc-Si. At the same time, Coulomb blockade plays an important role in the electronic transport in the nc-Si. The effect of thermal annealing in N₂ ambient on the electronic properties was studied and the results indicate that high temperature (1000°C) annealing can improve the size uniformity of the nc-Si prepared by decomposition of hydrogen-diluted silane.