IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 28, NO. 6, MARCH 15, 2016 701 Perimeter-Gated Single-Photon Avalanche Diodes: An Information Theoretic Assessment Jinlong Gu, Mohammad Habib Ullah Habib, and Nicole McFarlane, Member, IEEE Abstract— The performance of perimeter-gated single-photon avalanche diodes (PGSPADs) is assessed using principles of information theory. PGSPADs have an additional polysilicon gate to mitigate the effects of premature edge breakdown. Performance metrics of the photon detection probability and the dark count rate are experimentally obtained as functions of gate bias voltage and excess bias voltage. Applying the binary asymmetric communication channel model to the device, the parameter space that maximizes the information rate of the PGSPAD is assessed from the model and experimental data. Index Terms— Channel capacity, mutual information, photodetectors, single photon avalanche diodes. I. I NTRODUCTION S INGLE photon avalanche diodes (SPADs) are PN junctions operating in Geiger-mode. The devices are biased with a reverse voltage above the breakdown voltage. In this region of operation, a single photon can create a free carrier within the depletion region, which, under the effects of the high electric field, undergo impact ionization triggering an avalanche of charge carriers. Because of the planar nature of CMOS PN junctions, the electric field is maximum at the edge of the diodes’ periphery [2]. Thus, the periphery is more susceptible to breakdown than other areas when reverse-biased, and the periphery will enter breakdown prematurely affecting efficiency of the device. Recently, the addition of polysilicon gates at the perimeter of the diode have been added to reduce the electric field, thus mitigating the premature breakdown effect. These devices are called perimeter gated single photon avalanche diodes or PGSPADs [3]–[8]. Fig. 1. (a) shows the layout and cross- sectional view of an nwell-p+ PGSPAD. In recent years there has been significant interest in mod- eling biological and physical systems using communication channel models based on information theoretic principles. Information theory has been used to optimize and compare the design of operational amplifiers topologies, modify address event representation, data converters, study problems in mole- cular biology and neuroscience, optimizing the number of electrodes for a cochlea implant and study the effect of scaling Manuscript received July 17, 2015; revised November 15, 2015; accepted November 27, 2015. Date of publication December 3, 2015; date of current version February 18, 2016. The authors are with the Electrical Engineering and Computer Science Department, The University of Tenesseesee, Knoxville, TN 37996 USA (e-mail: jgu3@utk.edu; mhabib4@utk.edu; mcfarlane@utk.edu). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2015.2505241 Fig. 1. (a) Layout and cross-sectional view of the PGSPAD, (b) Com- munication channel model (top) and Binary Asymmetric Channel Model of PGSPAD (bottom), X = incident photon and Y = avalanche event. P on and P d are the transition probabilities. and noise processes on affinity based biosensors [9]–[26]. Additionally parallels between information theory and circuit theory have been performed [27]. Along these lines, there have been prior models of the information rate of silicon based photodetectors to enable more efficient detector use. These were applied to CMOS active pixel sensors and single photon avalanche diodes (SPAD) using Gaussian channel models [1], [28]–[31]. Considering the binary avalanche response of SPAD, a binary asymmetric channel model (BAC) was applied to analyze the perfor- mance of SPADs [29]. The information rate was determined using physics based probabilities and applied to InP and InAlAs SPADs without perimeter gate features. The infor- mation rate was determined as a function of the excess voltage and multiplication region width only. An important result of this work, was that the channel capacity (maximum information rate) was an appropriate measure for SPAD per- formance optimization [29]. Additionally, figure of merits, separate from the information rate, for CMOS SPADs, without a perimeter gate feature have also been proposed. These are based on the dark count rate (DCR) and photon detection probabilities (PDP) [32], [33]. In this letter, in order to determine the optimum para- metric space for perimeter gated single photon avalanche diodes (PGSPADs), we extend the aforementioned information theoretic concepts and models to model the Geiger mode operation as a function of perimeter gate bias and excess bias voltages. We model the probabilities directly as functions 1041-1135 © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.