A nonfundamental theory of low-frequency noise in semiconductor devices

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 attri buted to the traps a within the bandgap of a semiconductor, which are the s ources of the generation-recombination noise. The cumulative effect of the generation-recombination noise from each trap center generates a 1/f type n oise, it is shown that in fact, 1/f noise may have any frequency dependence between 1/f(0)-1/f(2). If not masked by thermal noise, the low-frequency n oise generated from these traps becomes 1/f(2) 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 re aches a plateau. While this theory can be applied to any semiconductor devi ce, only heterojunction bipolar transistors (HBTs) were considered in detai ls, Based on this theory, a model for low-frequency noise in the I,ase of H BTs is derived, Frequency and current dependence of low-frequency noise are modeled, Results of the base noise measurements in AlGaAs/GaAs HBTs were f ound to agree with the noise theory presented here. This significant theory , for the first time, proves the possibility of the number fluctuation mode l as a general 1/f noise cause without a need for specific and nonrealistic carrier lifetime probability functions.