Laser type of spectral narrowing in electroluminescent Si/SiO2 superlattices prepared by low-pressure chemical vapour deposition

Si/SiO2 superlattices were fabricated by low-pressure chemical vapour deposition. Superlattices of 75-150 nm layer pair thicknesses and having 1-8 layer pairs were investigated in order to evaluate their surface structure and electroluminescent properties. Atomic force microscopy (AFM) studies were performed in order to investigate the surface morphology of a thin SiO2 layer and to evaluate the sizes of polysilicon nanocrystals grown onto the top of it. The current-voltage characteristics and the electroluminescence spectra are also shown. We have observed a blueshift of over 200 nm in the electroluminescence peak wavelength by increasing the driving current. The change in the direction of the driving current through a sample changes the peak wavelength from the yellow to red region. In some samples, we could detect an exponential increase in light intensity in current densities near 100 mA per square millimeter. The increase in intensity is combined with a very prominent spectral narrowing of the electroluminescence spectra. The half width of this spectral peak was less than 5 nm, It is possible that we have observed for the first time a laser type of mechanism in semiconductor structures made solely of silicon and silicon dioxide. (C) 1999 Academic Press.