In this paper a novel technique to analyze the low-voltage breakdown regime of silicon diodes is presented. It is shown that the field emission tunnel current component of the reverse current does not cause energy transitions of carriers, and therefore will not emit photons. All photons being emitted from the pn junction are due to avalanche electroluminescence as a result of hot carrier energy relaxation processes. Measuring the light intensity output as a function of reverse current, the two current components (field
emission and impact ionization) can be extracted as a function of reverse voltage. The experimental
results were verified using the differential dynamic impedance method, as well as fitting a theoretical model to the extracted tunnel current. The temperature coefficient of current also indicated the transition from tunneling to avalanche.