Nonequilibrium carrier noise and its effects in microstructures

Abstract

Noise of nonequilibrium carriers confined to a limited volume of a semiconductor is discussed and compared with noise of unrestricted volume. Both high-and low-frequency noise of classical as well as quantum origin is considered. Classical high-frequency noise is closely related to heating of electrons e.g. by electric field. A full system of Boltzmann-like equations can be formulated to calculate the spectral density of the noise. An analysis of these equations shows that relatively slow mechanisms of relaxation can contribute to intermediate-frequency dispersion of the spectral density of current fluctuations. They are energy relaxation (for quasielastic electron collisions), intervalley relaxation (for many-valley semiconductors), generation-recombination (for intrinsic semiconductors). Each of these mechanisms becomes less efficient if the dimensions of the sample go below some critical value. A system of Langevin equations is formulated to analyse spatially nonhomogeneous fluctuations. Low-frequency noise of current-carrying electron gas may be produced by transitions in deep electron traps as well as by transitions of atoms (or small groups of atoms) between two equilibrium positions. The influence of the atomic transitions on electron mobility fluctuations is discussed. At low temperatures these are tunnel transitions while at higher temperatures they are activated. Physics of the quantum-mechanical low-frequency noise is discussed; its intensity is compared with that of the classical noise. Possible sources of noise in “collisionless” devices are also discussed.