Surface field reduction for planar semiconductor devices using oxygen doped amorphous silicon

A high breakdown voltage for a planar junction has been achieved by using a layer of oxygen doped amorphous silicon film over a composite of chemical-vapour deposition (CVD) phosphosilicate glass (PSG) film, CVD SiO2 film, and thermally oxidised SiO2. The high breakdown phenomenon was analysed from the viewpoint of surface depletion layer width. Measurements of the surface depletion layer width by scanning laser microscope, and numerical calculations of a 2-dimensional Poisson's equation for the distributed potential in oxygen doped amorphous silicon showed close agreement. The distributed potential of oxygen doped amorphous silicon influenced induction of the surface depletion layer, resulting in a reduced surface electric field and higher breakdown voltage. The leakage current of oxygen doped amorphous silicon was negligible at high temperatures (>125°C) compared to the normal junction leakage current. This was due to the low activation energy of conductivity for oxygen doped amorphous silicon.