This work presents the modeling of light emission from silicon based p+n junctions operating in avalanche breakdown. We revisit the photon emission process under the influence of relatively high electric fields in a reverse biased junction ( >105 V/cm). The photon emission rate is described as a function of the electron temperature Te , which is computed from the spatial distribution of the electric field. The light emission spectra lie around the visible spectral range ( λ∼ 300–850 nm), where the peak wavelength and the optical intensity are both doping level dependent. It is theoretically derived that a specific minimum geometrical width ( ∼170 nm) of the active region of avalanche is required, corresponding to a breakdown voltage of ∼5 V, below which the rate of photon emission in the desired spectrum drops. The derived model is validated using experimental data obtained from ultra-shallow p+n junctions with low absorption through a nm-thin p+ region and surface coverage of solely 3 nm of pure boron. We observe a peak in the emission spectra near 580 nm and 650 nm for diodes with breakdown voltages 7 V and 14 V, respectively, consistent with our model.