Photo- and electroluminescence from nanocrystalline silicon single and multilayer structures

Single and multilayer structures of nanocrystalline silicon/silicon dioxide (nc-Si/SiO2) were fabricated by alternate sequences of low-pressure chemical vapor deposition (LPCVD) of thin silicon layers and high temperature thermal oxidation. Silicon was deposited at 580°C and the obtained films were initially amorphous. During the high-temperature oxidation step, crystallization of the amorphous layer and simultaneous oxidation of the top layer was assured. The oxide thickness was controlled by controlling the oxidation time. Multilayers with five to ten periods were fabricated, with nc-Si thickness between 1.5 and 15 nm, and SiO2 thickness between 5 and 10 nm. Photoluminescence (PL) and transmission electron microscopy (TEM) were used to characterize the films. Nanocrystalline silicon layers of thickness below 5 nm showed 10 to 15 times more intense PL than those from thicker layers (12–16 nm thick). Electroluminescence (EL) was also studied and results will be discussed.