Study on the relation between surface roughness and the light emission spectrum of an Au–Al2O3–Al tunnel junction

We investigate the correlation between the light emission spectra of Au–Al2O3–Al junctions and the surface morphology of the junction obtained by atomic force microscopy (AFM). From the AFM micrographs, we find a self-correlation length of our junction of about 0.4 μm, which corresponds to surface plasmon polarition (SPP) energies of about 2.0, 1.76, and 1.3 eV at the Au–air, Al–Al2O3, and Au–Al2O3 interfaces, respectively. This agrees well with spectrum peaks observed at 630 nm (2.0 eV) and 700 nm (1.77 eV). A platform region from 800 to 850 nm (1.48 eV) in the spectrum is proposed to result from the overlap of SPP modes at the Au–Al2O3 and Al–Al2O3 interfaces. SPP modes at all three interfaces contribute to light emission via interface roughness in our system.