The results are presented of the simulation of th

Faulgaber, Alexander N.

Makarov, A. A.

Miroshnikov, B. N.

Zezin, D. A.

English

Tomsk State University Repository

SIMULATION OF THE SPECTRAL CHARACTERISTICS OF THE PHOTOSENSITIVE ELEMENTS BASED ON THE POLYCRYSTALLINE LEAD SULFIDE   B.N. Miroshnikov(a), D.A. Zezin(b), A.A. Makarov(c), A.N. Faulgaber(d)   (a),(b),(c),(d)National Research University “Moscow Power Engineering Institute”, Moscow, Russia (a),(b)Institute of Nanotechnology of Microelectronics of the Russian Academy of Science, Moscow, Russia (c)International Laboratory of Statistics of Stochastic Processes and Quantitative Finance of the National Research Tomsk State University, Tomsk, Russia  (a)MiroshnikovBN@mpei.ru, (b)ZezinDA@mpei.ru, (c)o_v_ch@mail.ru, (d)lytaleksandr@mail.ru     ABSTRACT The results are presented of the simulation of the spectral characteristics of the polycrystalline photosensitive elements based on the lead sulphide. The possible reasons for the experimental data discrepancy are discussed.  Keywords: photoresistors, lead sulfide, carrier lifetime, photosensitivity, spectral dependence  1. INTRODUCTION Lead sulfide (PbS) is one of the most needed narrow-band-gap semiconductors with the energy-gap width of 0.4 eV at 300 K. The photoresistors based on it are used in registering near infrared radiation (0.6-3.1 microns), i.e. they are integrated into impulse optoelectronic devices, IR detectors, infrared imagers, night viewing devices, etc. A wide variation of the methods for obtaining the devices mentioned above leads to the production of the patterns of various thicknesses, surface morphology and structure with the result that the spectral characteristics of the devices vary widely. The objective of this paper is to show the possibility of simulation of these photosensitive elements and to discuss the likely reasons why their theoretical characteristics differ from the experimental curves.  2. SIMULATION OF THE SPECTRAL CHARACTERISTICS OF PHOTORESISTORS As a basis, the experimental data presented by Ravich, Efimova and Smirnov (1968) are used. Mobility is estimated as 1 sVcm2  ; carrier (hole) lifetimes τ are chosen to be 50 µs for the “physical” element and 100 and 300 µs for the “chemical” element. The geometrical dimensions are: the photosensitive element area is , the thickness is 0.5 micron for the chemical layer and 1 micron for the physical layer. As a radiation source, the absolute black body is used. The temperature of the black body is 500 K, while its radiation spectrum is determined based on the Planck radiation formula. The relationship between the absorption coefficient and the incident radiation energy is taken from the study by Miroshnikov, Miroshnikova and Popov (2018). cm 1cm 1 In the general case, the dark carrier concentration is determined by the two components. They are:  related to the Auger recombination and carrier lifetime and obeying the ratio ; and  determined by the concentration of the acceptor-type traps and, especially, by the concentration of both chemically bound oxygen (it forms the deeper traps and increases the surface recombination rate at the crystallite surface) and physically adsorbed oxygen at the crystallite surface (Fig. 1). Our studies (Mohamed, Abdel-Hafiez, Miroshnikov, Barinov and Miroshnikova 2014) show that by heating the patterns up to the temperature of 400 K and degassing the surface, one can minimize the last component and obtain the minimum hole concentration which depends on the shallow trap concentration and is related to the carrier lifetime by the law 1p  scm1032 62721  p2p .   (1)  104.1 202 p Thus, the dark hole concentration     21darkdark pppp    (2)  depends on the carrier lifetime. For example, in Fig. 1, there are presented the dependences ,  (1) and  (2) as the functions of the carrier lifetime for the lead chalcogenides. 1p 2pdarkpThe carrier concentration in the presence of light ( ) is determined by the generation rate  depending on both the radiation wavelength λ and the photon penetration depth x: genp xG ,          , d  , , ABB xTNxG p     Proceedings of the European Modeling and Simulation Symposium, 2019 ISBN 978-88-85741-25-6; Affenzeller, Bruzzone, Longo and Pereira Eds. 34 Figure 1: The dependences of the hole concentration in lead chalcogenides upon the carrier lifetime  where is the radiation absorption coefficient;  is the number of photons incident in a unit of time (second) per unit of area ( ) and depending on both the radiation wavelength λ and the temperature of the radiation source (absolute black body – ABB);  is the quantum efficiency of the photoresistor close to unity. Thus, the total carrier concentration  is determined by the sum of the dark carrier concentration  (2) and the carrier concentration  under the lighting by source (ABB) radiation:   ABBT ,N p  genp2cmltpdarkp      . ,, gendark  ppplt  (3)  And, in turn, .       ,,gen xGpIn order to find the spectral dependence  of the current sensitivity, the following formula is applied:  IS      . , ABBTFIS pI    (4)  In Eq. (4), the designations are:  is the photocurrent,  pI hcNhNF pp  is the photon flux,  is the number of photons, h is the Planck constant, c is the velocity of light in free space, ν is the electromagnetic radiation frequency. For the photocurrent , one has: pN pI     ,  ltdp RVI     where  is the bias voltage (which is equal to 15 V) and dV        ddbdaR ltltltlt  1     is the incident radiation photoresistor resistance. Here  is the photosensitive element effective area which calcubahas been taken as square and equal to 1 2cm  for the lations; d is the photosensitive layer thickness;  lt  is the light photosensitive elemen istivity; t res  ,lt  is the light photosensitive element ctivity. ductivity conduThe con   ,lt  is primarily determined by the conductivit   ,p  due to the majority carriers, y that is, holes:            ,  ,,, ppp ,ltqp, nlt     where q p  is the hole  is an elementary charge, mobility close to 1 sVcm   and independent from the 2l in the first approximation,light leve  while  ,ltdetermined by the fo ). There are two main moses of absorption: ne ace (or non-uniform) absorption apar abso is rmula (3-surfnd uniform rption. From the Bouguer-Lambert law, it follows that all the absorption of the radiation incident on the surface occurs at the depth   1x . Then, when the ratio   1 d  is fulfilled, it was accepted that all the incident radiation is t a depth less than the ness, i.e. on the surface. On the other hand, if the inequality absorbed afilm thick   1 d  is satisfied, then it was assumed that the absorption is uniform. In the simulation d sulfide thin layers obtained by chemical deposition, it was presuppoof the leaat all the sed thabsorption is uniform. For thicker physical layers, both types of absorption were taken into account. In addition, the difference in the film technology also influences the efficiency of the radiation absorption by the layers   . Thus, the chemical layers are characterized by a large energy-gap width, and, therefore, radiation length longer than 3 microns is not absorbed, while for the physical layers, absorption in the near-surface region has less influence due to the thick layer of lanarkite ( 4PbSOPbOwave ). For our low-mobility samples, the condition dLp   is satisfied, that diffis, the hole use length   thpthan the photosensitive element thickness d, ere can be applied the formula for the concentration under the uniform absorption:     L  is mu andch less      ,  x . 2  GsLdsLpp    surface recombination rate. r-surface absorption, one gets: 1  ,,   xGgen where or theps is neaF            . 11  pp LsLd   pLs ,,  pLxGpgen Proceedings of the European Modeling and Simulation Symposium, 2019 ISBN 978-88-85741-25-6; Affenzeller, Bruzzone, Longo and Pereira Eds. 35 Figure 2: The calculated spectral characteristics for the photosensitive layers with the three lifetimes  In Fig. 2, there are presented the three calculated ithspectral characteristics of the photosensitive element: phys – for the physically deposited layer w  50   layer with μs,  – for the chemically deposited1100  μs and 2 chem  – for the chemically deposited layer with 300  μs.   chem a)  b) Figure 3: The experimental spectral characteristics (a) and the microphotography of the physical photosensitive element section obtained by means of he transmission high-resolutio ectron microscope (b) nt  RE Ulaye exp mental data (Fig. 3, orozova and Miroshnikov 2018).  tn elOur calculations and the comparison with the experimental data show that, for the physical layer, the transition from the near-surface absorption to the uniform one is realized when the value of the incideradiation wavelength is no less than 2 microns (curve phys in Fig. 2). If the incident radiation wavelength is bigger than 2.7 microns, then the absorption efficiency near the energies equal to the energy-gap width begins to be influential and the sensitivity begins decreasing. In turn, for the chemical layers (curves chem in Fig. 2), the uniform absorption is only taken into account, therefore, in the large wavelength range from 1.5 microns to 2.7 microns, the typical constant high reduced sensitivity is observed. The difference has also been determined under the various values of the lifetime affecting both the dark hole concentration  darkp  and the generated carrier concentration  ,genp .  3. DISCUSSION OF THE S LTS For the physically deposited er, the simulation coincides well with th eriM  a)  b) Figure 4: The experimental spectral characteristics (a) and the microphotography of the section of the photosensitive element surface obtained by means of the chemical deposition w e maximum sensitivity (b) ith thProceedings of the European Modeling and Simulation Symposium, 2019 ISBN 978-88-85741-25-6; Affenzeller, Bruzzone, Longo and Pereira Eds. 36The difference in the slope of the curve in the high-energy spectral region (up to 2.3 microns) is determined by the thickness of the non-photoactive layer of the lead oxides colored by the light colors in Fig. 3b. The results of the simulation of the spectral  this case s ppear to be close to the experimental data. nto account relaxation processes  of the dark  Ministry of Education and Science of the ussian Federation (research project No. Council on grants of the  PbSe, PbS lead chalcogenides [in Russian]. Moscow: Nauka. ., Miroshnikova I.N. and Popov A.I., Moh ., Miroshnikov B.N., aterials Morocs of the Solid State, 52 (3), 295-298. AUTBoriHe r s from the National Research University “Moscow Power . Boris N. Miroshnikov is cow Power Engineering Institute” in 2014. He is currently working as an Power Engineering Institute” in 2014 and 2016, respectively, both in radio esearch University “Moscow Power Engineering Institute” in 2014 and 2016, respectively, characteristics of the photosensitive element obtained by the chemical method also agree well with the experimental data (Fig. 4, Morozova and Miroshnikov 2018). What has not been taken into account inis the change in the lead sulfide energy-gap width due to the effect of the oxygen in PbS structure that is the isoenergetic impurity resulting in a local change in the energy-gap width of the material (Morozova and Miroshnikov 2018). This is the first reason for the conformity between the simulation results and the experimental data. Another reason is the small photosensitive element thickness – 0.5 micron, resulting in the long-wavelength (low-energy) radiation part passing through the film without the photo-ionization.  4. CONCLUSION Thus, it has been established that the simulation can be implemented of such complex structure as the polycrystalline photosensitive element and its resultaThe simulation takes iboth inside the crystallites (Auger recombination) and the effect of oxygen-containing impurities on the surface, leading to the capture of free electrons, an increase in the hole lifetime and stabilizationconductivity.  ACKNOWLEDGMENTS This research was financially supported by the Russian Foundation for Basic Research (research project No. 18-29-11051), theR2.3208.2017/4.6), and the President of the Russian Federation (research project No. SP-834.2019.3).  REFERENCES Ravich Y.I., Efimova B.A. and Smirnov I.A., 1968. Methods for the study of semiconductors as applied to PbTe,Miroshnikov B.N2018. Optimization of parameters of PbS-based polycrystalline photoresistors. Semiconductors or Physics of the Solid State, 52 (2), 245-249. amed H.S.H., Abdel-Hafiez MBarinov A.D. and Miroshnikova I.N., 2014.  Spectral characteristics and morphology of nanostructured Pb-S-O thin films synthesized via two different methods. Journal of MScience in Semiconductor Processing, 27, 725-732. zova N.K. and Miroshnikov B.N., 2018. Isoelectronic oxygen centers and conductivity of CdS in comparison with PbS. Semiconductors or Physi HORS BIOGRAPHY s N. Miroshnikov was born in Moscow in 1990. eceived his Ph.D. in semiconductor physicEngineering Institute” in 2016currently working as an Assistant Professor at the Department of Electronics and Nanoelectronics of the National Research University “Moscow Power Engineering Institute”. He also works as a Researcher at the Institute of Nanotechnologies of Microelectronics of the Russian Academy of Science. His main interests are physics and technology of infrared photodetectors based on single- and polycrystals.  Denis A. Zezin was born in 1988. He received his Ph.D. in solid-state electronics from the National Research University “MosAssociate Professor at the Department of Electronics and Nanoelectronics of the National Research University “Moscow Power Engineering Institute” as well as a Researcher at the Institute of Nanotechnologies of Microelectronics of the Russian Academy of Science. His research interests relate to the study of the electrophysical visible and infrared radiation-measuring instruments. Alexander A. Makarov was born in 1993. He received the B.Sc. and the M.Sc. degrees from the National Research University “Moscow engineering. Presently, Alexander A. Makarov is a PhD student in the Department of Electronics and Nanoelectronics at the National Research University “Moscow Power Engineering Institute” as well as he is working as a Researcher at the International Laboratory of Statistics of Stochastic Processes and Quantitative Finance of the National Research Tomsk State University. His research interests include synthesis, analysis and simulation of the processing algorithms of stochastic processes and fields with unknown parameters. Alexander N. Faulgaber was born in 1993. He received the B.Sc. and the M.Sc. degrees from the National Rboth in radio engineering. Presently, Alexander N. Faulgaber is a PhD student in the Department of Electronics and Nanoelectronics at the National Research University “Moscow Power Engineering Institute”. His research interests include synthesis, analysis and simulation of the processing algorithms of stochastic processes and fields with unknown parameters. Proceedings of the European Modeling and Simulation Symposium, 2019 ISBN 978-88-85741-25-6; Affenzeller, Bruzzone, Longo and Pereira Eds. 37

Simulation of the spectral characteristics of the photosensitive elements based on the polycrystalline lead sulfide

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Simulation of the spectral characteristics of the photosensitive elements based on the polycrystalline lead sulfide

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