Electroluminescence (EL) spectra of nanoscale diodes formed after gate-oxide breakdown of n+-polysilicon/oxide/p+-substrate metal–oxide–semiconductor capacitors were measured in reverse and forward bias. The nanoscale diodes, called diode antifuses, are created by the formation of a small link between the n+-poly and the p+-substrate with the properties of a diode. A previously published multimechanism model for avalanche emission from conventional silicon p–n junctions is applied to fit the EL spectra in reverse-biased silicon-diode antifuses. The results show that the light from reverse-biased diode antifuses is caused by the same phenomena as in conventional p–n junctions. Forward-bias spectra of the diode antifuses show different shapes when lightly or highly doped p substrates are used. In the case of a lightly doped p substrate, the EL intensity in the forward mode is increased by about two orders of magnitude in the visible-wavelength range with a maximum intensity in the infrared region. A phonon-assisted electron–hole recombination model is applied to fit the low-energy part of emitted spectra. The visible emission is attributed to the Fowler–Nordheim tunneling current through the SiO2, enabled presumably by electron capture into SiO2 trap levels and intraband transition of hot electrons injected into the Si bulk.