Characterisation of room temperature blue emmiting Si/SiO₂ multilayers

In this study we report results on a series of Si/SiO₂ multilayers periods deposited by standard CMOS processes on thermally oxidised Si substrates. Each period was formed by alternating a low-pressure chemical vapour deposition (LPCVD) nanocrystalline silicon thin film and a SiO ₂ thin film obtained by atmospheric pressure chemical vapour deposition (APCVD). High-resolution TEM (HRTEM) and Raman spectroscopy have been used for the physical characterisation of the nc-Si/SiO₂ multilayers. The HRTEM analysis revealed a columnar structure, with an average grain size of 15 nm for the silicon layers. The Si-SiO₂ interfaces were smooth with a surface roughness for silicon layers less than 1 nm, as estimated from HRTEM analysis. Raman measurements demonstrate that the nanocrystalline silicon (nc-Si) layers are free-of-stress. Room temperature photoluminescence (PL) spectra, obtained by using a 325 nm continuous wave (CW) laser excitation, showed a broad blue peak centred on 440 nm. The intensity of the blue PL band increased with the number of periods in the nc-Si/SiO ₂ multilayers. The origin of this intense room temperature blue PL band is discussed.