Abstract
A general low-frequency noise theory based on the fluctuation in the number of carriers is presented. In this theory, the low-frequency noise is attributed to the traps within the bandgap of a semiconductor, which are the sources of the generation-recombination noise. The cumulative effect of the generation-recombination noise from each trap center generates a 1/f type noise. It is shown that in fact, 1/f noise may have any frequency dependence between 1/f/sup 0/-1/f/sup 2/. If not masked by thermal noise, the low-frequency noise generated from these traps becomes 1/f/sup 2/ at very high frequencies. Also, if the lifetime of the carriers in the semiconductor under nonequilibrium condition is finite, at very low frequencies, the noise spectral density reaches a plateau. While this theory can be applied to any semiconductor device, only heterojunction bipolar transistors (HBTs) were considered in detail. Based on this theory, a model for low-frequency noise in the base of HBTs is derived. Frequency and current dependence of low-frequency noise are modeled. Results of the base noise measurements in AlGaAs/GaAs HBTs were found to agree with the noise theory presented here. This significant theory, for the first time, proves the possibility of the number fluctuation model as a general 1/f noise cause without a need for specific and nonrealistic carrier lifetime probability functions.
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