Excess white noise in bipolar junction transistors

White noise of the collector current is experimentally investigated in transistor structures for which the values of the spectral density of this noise as well as the behaviour of its temperature and current dependencies point to the excess nature of the noise observed. It is shown that the noise characteristics studied may be completely explained in the frames of the model, suggesting that the noise results from the fluctuations of the width of the transistor base region. Those fluctuations are due to the fluctuations of the width of the emitter junction. These latter are connected with spontaneous changes of the charge on the local centres in the junction.