Passivation of Liquid-Phase Crystallized Silicon With PECVD-SiN_x and PECVD-SiN_x/SiO_x

Silicon nitride (SiN_x) and silicon oxide (SiO_x) grown with plasma-enhanced chemical vapor deposition are used to passivate the front-side of liquid-phase crystallized silicon (LPC-Si). The dielectric layer/LPC-Si interface is smooth and layers are well-defined as demonstrated with transmission electron microscopy. Using electron energy loss spectroscopy a thin silicon oxynitride is detected which is related to oxidation of the SiN_x prior to the silicon deposition. The interface defect state density (D_it) and the effective fixed charge density (Q_IL,eff) are obtained from high-frequency capacitance-voltage measurements on developed metal-insulator-semiconductor structures based on SiO_x/SiN_x/LPC-Si and SiO_x/SiN_x/SiO_x/LPC-Si sequences. Charge transfer across the SiN_x/LPC-Si interface is observed which does not occur with the thin SiO_x between SiN_x and LPC-Si. The SiO_x/SiN_x/LPC-Si interface is characterized by Q_IL,eff> 10¹² cm⁻² and D_it,MG>10¹² eV⁻¹cm⁻². With SiO_x/SiN_x/SiO_x stack, both parameters are around one order of magnitude lower. Based on obtained Q_IL,eff and D_it(E) and capture cross sections for electrons and holes of σ_n = 10⁻¹⁴ cm s⁻¹ and σ_p = 10⁻¹⁶ cm s⁻¹, respectively, a front-side surface recombination velocity in the range of 10 cm s⁻¹ at both interfaces is determined using the extended Shockley-Read-Hall recombination model. Results indicate that field-effect passivation is strong, especially with SiO_x/SiN_x stack.