Photoinduced and thermal noise in semiconductor $p-n$ junctions

A brief review of the literature on the theory of thermal and photoinduced noise in semiconductor $p-n$ junctions is given. The coordinate and frequency dependences of photoinduced noise in a $p^{+}-n$ junction with a locally irradiated $n$-region are calculated. In contrast to vacuum tubes, where the physical sources of current distribution noise are still unknown, it is established that in $p^{+}-n$ junctions, this noise is produced by fluctuations in the local hole recombination and diffusion rates in the $n$-region. White high-frequency spectra of thermal and photoinduced noise arise when the hole concentration increases linearly outside the space charge region and occur because the diffusion noise currents and the effective length for collecting noise from the $n$-region compensate each other in terms of frequency dependence.