Abstract
Hydrogen amorphous silicon nitride (a-SiNx:H) thin films have been prepared by plasma enhanced chemical vapor deposition(PECVD) using a mixture of 5﹪silane (SiH4)in argon (Ar) and nitrogen(N2). Most films exhibited visible photoluminescence (PL) and some emited strong PL after thermal annealing. The PL main peak position was found to be dependent on reactive gas flow ratio (N2/N2+SiH4=G). We obtained full color photoluminescence (Red, Orange, Yellow, Green, Blue, White) and they are sequentially adjustable and have been seen by naked eye in daylight room. We suggest that PL are originated from Si clusters (size dependence) or defect level that form during PECVD growth and crystallize or hydrogen escape upon annealing. The PL properties of these films with no oxygen content are similar to those of silicon oxide SiOx (0<x<2) or silicon oxynitride (SiOxNy:H) films and porous silicon. We suppose that nitrogen could play a role for the luminescence properties. Properties of these films were measured by means of X-ray photoelectron spectroscopy (XPS). The composition of x was determined by XPS. These films microstructure bonding configuration was examined by Fourier Transform infrared (FTIR) spectroscopy. The variation of coordinating atoms of Si 2p core-level was observed in XPS analysis. The peak of Si 2p binding energy shift from 99.7eV toward 102.4eV.The silicon clusters and multi-phases existing in these films were suggested to be associated will the random bonding model. Visible electroluminescence from an Au/thin a-SiNx:H layer/p-type Si or Al/a-SiNx:H/ITOglass structure has been observed.These structures emit only white light when a forward bias larger than 20V was applied,and which could be seen by naked eye in dark room, while no EL was observed under the reverse bias. The EL intensity was increased with the applied voltage. These results indicate that the thin a-SiNx:H layer plays a key role in light emission from the Au/thin a-SiNx:H layer/p-type Si structure. The possible mechanism are that electrons and holes from opposite sides tunneling into the thin a-SiNx:H layer and radiatively recombined at the luminescence center(LC). It's still difficult to attribute radiative recombination of electron-hole pairs in nano size silicon clusters.