Light-emission mechanism of Si-MOS tunnel junctions

The light-emission mechanism of Si-MOS (metal-oxide-semiconductor) junctions has been investigated. Si/${\mathrm{SiO}}_2$/metal (Al or Au) MOS junctions with extremely smooth interfaces were fabricated by taking advantage of the well-developed Si processing technology. The observed light-emission spectra can be accounted for by the current fluctuation theory of light-emitting tunnel junctions [B. Laks and D. L. Mills, Phys. Rev. B 20, 4962 (1979)]. There are two channels of light emission: the direct emission from the fluctuation of the tunneling current and the indirect emission that arises from the scattering (by surface roughness) of surface-plasmon polaritons generated by the fluctuating tunnel current. The light from the Si/${\mathrm{SiO}}_2$/Al junction arises mainly from the direct emission from the fluctuating current. The light from the Si/${\mathrm{SiO}}_2$/Au junction contains both the direct and indirect emissions with approximately equal strengths. The direct and indirect emissions have comparable strength in our junctions, because our Si-based junctions are extremely smooth and the indirect emission is much weaker than in the junctions used in earlier studies.