Effects of contact metals on electroluminescence from embedded nanosize-Si-particle films

Sandwich structures composed of metal and Si external layers with an intermediate embedded nanosize-Si-particle insulator layer have been fabricated. The insulator layer is composed of extra thin (∼80 Å) Si-rich silicon dioxide (ETSSO) films or extra thin (∼80 Å) silicon oxynitride (ETSON) films. Semitransparent Au, Pd, Ag, and Al films were used as contact metals. The effects of metal contacts on electroluminescence (EL) from the structures under forward biases are reported. For structures with either ETSSO and ETSON insulator layers, the EL peak positions appear at a distinctly longer wavelength when the contact metal has a large work function, such as Au or Pd, when compared with structures where the contact metal has a lower work function, such as Ag or Al. For a single contact metal, the EL peak position is almost independent of forward biases. The experimental results are difficult to be explained with a model of band to band radiative recombination of electron-hole pairs in nanosize Si particles, but can be better explained by a model in which electrons and holes tunnel into the insulator layer and radiatively recombine at the luminescence centers there. The metal work functions affect which types of luminescence centers determine the EL.