Noise generation-recombination

Noise due to carrier number fluctuation is connected with detector bias and is denoted as shot noise or Schottky noise [5]. It is also denoted as the excess noise, but this expression is also sometimes used for 1//noise [62]. It is a consequence of carriers passing through energy barriers, i.e., it appears as a result of the statistic nature of interband transitions and transitions band-impurity level, and in the final instance it is a consequence of the discrete nature of carriers [63]. When carrier number fluctuations are caused by g-r processes, this noise is also denoted as generation-recombination (g-r) noise. 

For our present consideration g-r noise is the most important noise mechanism. The g-r noise spectmm is flat (white) up until the cutoff frequency, approximately given as the reciprocal value of free carriers lifetime. For the component of this noise not connected with illumination in a case of an ideal photoconductive detector one may write [7] 

The above means that in both cases noise current is proportional to the total number of generation-recombination acts. 

The above consideration does not encompass the very important f noise (flicker noise, current noise, modulation noise). It is marked at lower frequency ( pink noise ) and becomes negligible in comparison to g-r noise at a knee frequency, a value that may be anywhere between several Hz and 100 MHz, depending on a particular device. In a general case flicker noise is given by the general empirical relation [64] 

A generally accepted theory of 1/f noise does not exist, although a large body of papers was published on this topic. Most of them start with the assumption that this type of noise is a consequence of stochastic fluctuations of either the density of free carriers or their mobility [61]. This noise can be, thus, connected with the effective scattering cross section in material and is often considered a consequence of the existence of potential barriers on the surface or in the bulk of semiconductor [8]. 1// noise on the surface is caused by the transitions of carriers connected with slow surface states and with detector electrical contacts [64]. Often (but not always) this noise may be minimized by convenient technological procedures for surface treatment and Ohmic contact fabrication. Thus, it may be regarded more a technological than a fundamental problem. 

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The detector of GB-A-2260218 comprises a photo-responsive material and an array of planar antennae formed thereon which concentrate radiation in fringe fields at antenna edges and extremities interacting with the photo-responsive material. This structure allows the photo-responsive material to be formed thinly, which reduces volume-dependent generation-recombination noise with consequent increase in responsivity and detectivity. Furthermore, reduced element thickness allows higher element resistance. 

For Kinetic Inductance Detectors the fundamental noise source is the quasiparticle generation-recombination noise (Visser et al. 2012 Baselmans et al. 2008). To integrate this source of noise in the simulation, the first step is to compute the density of quasiparticles per unit volume in a superconductor in thermal equilibrium, this is... 

P.J. Visser, J.J.A. Baselmans, P. Diener, S.J.C. Yates, A. Endo, T.M. Klapwijk. Generation-recombination noise The fundamental sensitivity hmit for kinetic inductance detectors. J. Low Temp. Phys. 167(3 ), 335-340 (2012). ISSN 0022-2291. doi 10.1007/sl0909-012-0519-5... 

Fleischmann, M. and Oldfield, J.W. (1970) Generation- recombination noise in weak electrolytes. Journal of Electroanalytical Chemistry, 27, 207. 

We consider further the determination of local values of generation-recombination noise for the case when carrier concentration within detector is position-dependent, i.e., when g-r rate and photoelectric gain are spatially inhomogeneous. We use such spatial distribution to determine total noise current (g-r plus thermal) through the whole detector. For the sake of simphcity, we assume that the gradient exists only along one direction, parallel to the y-axis. We consider a photocon-ductive device. 

Further, we calculate the total noise current as a sum of the squares of generation-recombination noise current obtained in the above manner and Johnson-Nyquist (thermal) current... 

Minority carrier exclusion was chronologically the first nonequilibrium effect to be described within the context of its use in infrared detectors for Auger processes suppression. In 1985 British researchers Ashley and Elliott published a paper [356] that introduced the concept of nonequiUbrium suppression of Auger processes (including generation-recombination noise) at near-room temperatures. In that paper they proposed the use of the exclusion effect to that pmpose. In the same year White published a detailed numerical and experimental analysis of exclusion devices [50]. In that paper he presented an approximate analytical model for determination of most important parameters of exclusion photoconductors. 

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