Shot or quantization noise is related to the quantized nature of charge and the individual carrier injection through the pn junction. Particles of charge flow with random spacing. The noise is white and proportional to the DC current. Statistical analysis of the random occurrence of particle flow yields that the mean square current variations are uniformly distributed in frequency up to the inverse of the transit time of carriers across the device.
The mean squared value of the noise current is
where e is the charge of the electron, idc is the average dc diode current, and Δf is the bandwidth of the measuring instrument.