This work presents the modeling of light emission from silicon based pþn 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 (k 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 5V, below which the rate of photon emission in the desired spectrum drops. The derived model is validated using experimental data obtained from ultra-shallow pþn junctions with low absorption through a nm-thin pþ 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 7V and 14 V, respectively, consistent with our model.