Measurements of non-Gaussian noise in quantum wells

Abstract

Gaussian generation-recombination is accepted to be a dominant mechanism of current noise source in quantum well systems biased by electric field normal to the layers. We have found pronouncedly non-Gaussian excess current noise in $n$-type and $p$-type multiple quantum wells. The non-Gaussian noise has been attributed to metastable spatial configurations of electric field. The metastability likely originates from negative differential conductance caused by intervalley scattering in $n$-type wells and heavy and light holes tunneling in $p$-type wells. At a constant bias, the quantum well system randomly switches between a high resistivity state with low current flow and low resistive state with high current flow. The non-Gaussianity of the noise is more pronounced in $p$-type wells where the time traces of current fluctuations resemble closely a two-level random telegraph signal, which has not been straightforwardly observed in $n$-type wells. The non-Gaussian character of the noise in $n$-type systems has been revealed by measurements of nonzero skewness of the amplitude distributions. The difference between noise properties of $n$- and $p$-type systems has been attributed to small capture probability of electrons in $n$-type wells, as opposed to very high capture probability of holes in $p$-type wells. As a consequence, the noise of any $p$-type multiwell system is dominated by fluctuations of a single well, while in the $n$-type the noise appears as a superposition of many fluctuators associated with individual wells.