Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit

Analysis is made for the possibility of redistribution of mobile point defects in a semiconductor after its exposure to the electric field till the stationary conditions in the crystal are reached. Two different ways of applying the voltage are considered: (i) directly to the sample, (ii) to a capac...

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Datum:1998
Hauptverfasser: Kashirina, N.I., Kislyuk, V.V., Sheinkman, M.K.
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Sprache:English
Veröffentlicht: Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України 1998
Schriftenreihe:Semiconductor Physics Quantum Electronics & Optoelectronics
Online Zugang:http://dspace.nbuv.gov.ua/handle/123456789/114667
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Zitieren:Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit / N.I. Kashirina, V.V. Kislyuk, M.K. Sheinkman // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1998. — Т. 1, № 1. — С. 41-44. — Бібліогр.: 12 назв. — англ.

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spelling irk-123456789-1146672017-03-12T03:02:11Z Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit Kashirina, N.I. Kislyuk, V.V. Sheinkman, M.K. Analysis is made for the possibility of redistribution of mobile point defects in a semiconductor after its exposure to the electric field till the stationary conditions in the crystal are reached. Two different ways of applying the voltage are considered: (i) directly to the sample, (ii) to a capacitor, with the sample located between the plates. This model is applicable also to the electric field of any nature, whether external or internal, e.g. that arisning at the metal-semiconductor interface. Дається аналіз можливості розподілу рухомих точкових дефектів в напівпровіднику після дії на нього електричного поля до встановлення стаціонарних умов. Розглядаються два способи прикладання напруги: а) безпосередньо до зразка, б) до обкладинок конденсатора, між якими поміщається зразок. Модель також можна застосовувати для електричних полів будь-якої природи . як зовнішніх так і внутрішніх, що виникають, наприклад, на контакті метал-напівпровідник. Приводится анализ возможности распределения точечных дефектов в полупроводнике после воздействия на него электрического поля до установления стационарных условий. Рассматривается два способа приложения напряжения: а) непосредственно к образцу, б) к обкладкам конденсатора, между которыми помещается образец. Модель также применима для электрических полей любой природы как внешних так и внутренних, возникающих, например, на контакте металл-полупроводник. 1998 Article Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit / N.I. Kashirina, V.V. Kislyuk, M.K. Sheinkman // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1998. — Т. 1, № 1. — С. 41-44. — Бібліогр.: 12 назв. — англ. 1560-8034 PACS 61.72; 71.55. http://dspace.nbuv.gov.ua/handle/123456789/114667 539.219.3 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
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description Analysis is made for the possibility of redistribution of mobile point defects in a semiconductor after its exposure to the electric field till the stationary conditions in the crystal are reached. Two different ways of applying the voltage are considered: (i) directly to the sample, (ii) to a capacitor, with the sample located between the plates. This model is applicable also to the electric field of any nature, whether external or internal, e.g. that arisning at the metal-semiconductor interface.
format Article
author Kashirina, N.I.
Kislyuk, V.V.
Sheinkman, M.K.
spellingShingle Kashirina, N.I.
Kislyuk, V.V.
Sheinkman, M.K.
Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
Semiconductor Physics Quantum Electronics & Optoelectronics
author_facet Kashirina, N.I.
Kislyuk, V.V.
Sheinkman, M.K.
author_sort Kashirina, N.I.
title Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
title_short Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
title_full Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
title_fullStr Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
title_full_unstemmed Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit
title_sort theoretical approach to electrodiffusion of shallow donors in semiconductors: i. stationary limit
publisher Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
publishDate 1998
url http://dspace.nbuv.gov.ua/handle/123456789/114667
citation_txt Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit / N.I. Kashirina, V.V. Kislyuk, M.K. Sheinkman // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1998. — Т. 1, № 1. — С. 41-44. — Бібліогр.: 12 назв. — англ.
series Semiconductor Physics Quantum Electronics & Optoelectronics
work_keys_str_mv AT kashirinani theoreticalapproachtoelectrodiffusionofshallowdonorsinsemiconductorsistationarylimit
AT kislyukvv theoreticalapproachtoelectrodiffusionofshallowdonorsinsemiconductorsistationarylimit
AT sheinkmanmk theoreticalapproachtoelectrodiffusionofshallowdonorsinsemiconductorsistationarylimit
first_indexed 2025-07-08T07:46:56Z
last_indexed 2025-07-08T07:46:56Z
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fulltext 41© 1998 ²íñòèòóò ô³çèêè íàï³âïðîâ³äíèê³â ÍÀÍ Óêðà¿íè Ô³çèêà íàï³âïðîâ³äíèê³â, êâàíòîâà òà îïòîåëåêòðîí³êà. 1998. Ò. 1, ¹ 1. Ñ. 41-44. Semiconductor Physics, Quantum Electronics & Optoelectronics. 1998. V. 1, N 1. P. 41-44. ÓÄÊ 539.219.3; PACS 61.72; 71.55. Theoretical approach to electrodiffusion of shallow donors in semiconductors: I. Stationary limit N. I. Kashirina, V. V. Kislyuk, M. K. Sheinkman Institute of Semiconductor Physics, NAS Ukraine, 45 prospekt Nauki, Kyiv, 252028, Ukraine Phone/Fax: +044 265 63 40; E-mail: moishe@photel.semicond.kiev.ua Abstract. Analysis is made for the possibility of redistribution of mobile point defects in a semiconduc- tor after its exposure to the electric field till the stationary conditions in the crystal are reached. Two different ways of applying the voltage are considered: (i) directly to the sample, (ii) to a capacitor, with the sample located between the plates. This model is applicable also to the electric field of any nature, whether external or internal, e.g. that arisning at the metal-semiconductor interface. Keywords: Electrodiffusion, CdS, mobile donors. Paper received 14.07.98; revised manuscript received 25.08.98; accepted for publication 27.10.98. 1. Introduction Mobile point defects in semiconductors result in degrada- tion of semiconductor devices. Mobile point defects in II�VI compounds are the principal reagent in photochemi- cal reactions found to affect the photosensitivity [1] and lu- minescence of laser screens [2], to give rise to conducting channels [3] and to change the properties of metal-semicon- ductor junctions [4, 5]. Since semiconductor devices are based mainly on p-n- or hetero-junctions, there always is an internal electric field to act on the mobile charged defects. Manufacturers of very large scale Si solar cells have a prob- lem with the mobility of drifting interstitials, which is sub- stantially high even at moderate temperatures [6]. The drift of mobile defects can be utilized to redistrib- ute them, decreasing thereby their content within some part of a crystal [7, 8]. Cadmium sulfide is a non-stoichiometric compound with inhomogeneity diagram shifted to the excess of cadmium at room temperature [9]. The excess cadmium occupying interstitials (Cdi) in CdS is a shallow donor (E c � E d = = 0.03 eV) with a rather high mobility (activation energy about 0.4�0.6 eV) at moderate temperatures (300�400 K). This paper presents a model which describes the final distribution of defects after exposure to the electric field. The model assumes a constant charge state of the drifting ions. This problem was considered for the case of cadmium sulfide. 2. Theoretical background One-dimensional diffusion-drift equation was used for the electron subsystem in conjunction with Poisson�s equation and Boltzmann distribution of charged Cd+ ions (stationary conditions). With D n being electron diffusivity, the electron current is expressed as: r r r i en eD n n n = − ∇ + ∇µ ϕ , (1) where ϕ is the electric field potential, and n is the electron concentration. The singly charged mobile donors are distributed in ac- cordance with the Boltzmann law: N x N e x kT Cd Cd L( ) exp ( )= −      ϕ , (2) where N Cd (x) is the concentration of Cd mobile interstitials. With boundary conditions: N L N Cd Cd L( ) = ; ϕ( )L = 0 (cathode); ϕ ϕ( )0 0= (anode). Equations (1) and (2) have to be complemented with Poisson�s equation defining the relation between the poten- tial ϕ( )x and charge density ρ( )x : d dx x 2 2 4ϕ π ε ρ= − ( ) , (3) N. I. Kashirina et al.: Theoretical approach to electrodiffusion... 42 ÔÊÎ, 1(1), 1998 SQO, 1(1), 1998 where ρ( ) ( ( )x e Z N Z N n x d d a a = + − + + N x Cd ( )) , (hereinafter Z d = 1; Z a = �1) (4) Writing electron density as a function of the potential from equation (1), with Boltzmann�s distribution (2) taken into account for the concentration of the mobile Cd ions, we obtain the integro-differential equation for the dimensionless potential ψ ϕ( ) ( ) /x e x kT= :       ∆−−+= −−∫ NeNendxe L e eD i kT e dx d L Cd L x Ln ψψψψ ε πψ )()( 2 2 2 14 (5) where i en D L L n0 = / , n n L L = ( ) . The diffusivity D n and mobility µn are connected by Einstein�s equation. Equation (5) can be easily rewritten in terms of the elec- tric field: ∂ ∂ ∂ ∂ π ε π ε ψ 2 2 24 2 4 0 E x e kT E E x e kT N e N E i kT e kT Cd L + − × × + + =−( )∆ (6) where ∆N N N d a = − . At N Cd L = 0 eq. (6) transforms into the well-known equa- tion for the field distribution in the space charge region [10]. The presence of mobile donors actually expands the space charge region over Debye�s length, determined as: L kT e n Z D k k k = ∑         ε π4 2 2 1 2 , where Zk is the charge of k th component, to the whole length of the crystal. Equation (6) can be solved by the successive approxi- mation method. As a zero-order approximation, we can take the N Cd (x) distribution calculated in the quasi-neutrality ap- proach. Substituting this zero approximation N Cd (x) into eq. (6), we can analyze the current-voltage dependence in the first approximation. The convergence of this technique is determined by L D /L ratio. 3. Results and discussion The right side of eq. (5) is zero in the quasi-neutrality ap- proach, and thus we get the potential Ψ as an implicit func- tion in the expression: x L F F = −1 0 ( ) ( ) ψ ψ , where F e N N Cd L ( ) ;ψ ψψ= − −− ∆ 2 1 . (7) Depending on the positive or negative charge of the «background» (corresponding to the sign of ∆N), (7) tends to behave in essentially different ways. While for ∆N ≥ 0 there is a continuous solution of eq. (7) (At ∆N = 0 it be- comes identical to the expression used in the theory of bi- nary electrolytes [11]), this does not occur if the «back- ground» charge is negative. In the latter case, the solution has a break, which indi- cates that the electroneutrality approach is not valid. At any rate, both cases have similar solutions for Ψ 0 3 (fig. 1).≤ Fig. 1. Redistribution of Cd+ concentration for a system which in- cludes: (1) � three components (electrons + Cd i + immobile accep- tors; N a /NL Cd+ = 0.1); (2) � two components; (3) � three components (electrons + Cd i + immobile donors; N d /NL Cd+ = 0.1). Fig. 2. Redistribution of Cd+ concentration and voltage (in terms of dimensionless potential ψ) in the case of posi- tive «background» for various values of current: 1 � i/i 0 = = 3; 2 � i/i 0 = 5; 3 � i/i 0 = 10. 0,0 0,2 0,4 0,6 0,8 1,0 0 20 40 60 80 100 0 2 4 6 8 10 ψ x/L 3 2 1 3 2 1 ψ 0,0 0,2 0,4 0,6 0,8 1,0 0,0 0,5 1,0 1,5 2,0 x/L ψ 0 =3 1 2 3 N N Cd Cd = i 0,00 0,01 0,08 0,12 2 1 3 x/L cathode N N Cd Cd = N N Cd Cd = anode anode catode N. I. Kashirina et al.: Theoretical approach to electrodiffusion... 43ÔÊÎ, 1(1), 1998 SQO, 1(1), 1998 The result obtained for the system with immovable posi- tively charged background is the most attractive, since these conditions allow extending the low Cd+ content zone (fig. 2, curves 1, 2, 3 correspond to i/i 0 = 3, 5, 10, respec- tively). When i i/ 0 value is rather low, the first term in the pa- rentheses in eq. (5) becomes: { } ∂ ψ ∂ π ε ψ ψ 2 2 24 x e k T n e N e N L C d L = × × − −− ∆ (8) which describes the electric field between the plates of a capacitor. Eq. (8) with ∆N = 0 and boundary conditions: ψ ψ ψ ψ( ) / ; ( ) /0 2 20 0= = −L transforms into the Poisson-Boltzman equation: { }∂ ψ ∂ π ε ψ ψ 2 2 2 04 x e kT n e e= − − (9) which is solved analytically for x ≥ 0 at boundary condi- tions taken as: x → ∝ ; ψ′ → 0, and the other condition usually determines the value of the field at x = 0. The value of the field in the sample at i/i 0 ~ 0 is negligible at x far from the edges of the crystal (fig. 3). The potential distribution within the space charge region (SCR) is determined by the following integral: x L d e eD = + −−∫ ψ ψ ψ ψ ψ 2 0 2/ . (10) A surface charge confined by the external field within a thin (~L D thickness) within surface layer is calculated by Q eL n e e d e e D= − + − − −∫0 2 2 1 0 ( ) / ψ ψ ψ ψ ψ ψ ψ , (11) where ψ 1 = ψ (L D ); e, n 0 are the lectron charge and concen- tration in the bulk where it equals the donor concentration N Cd 0 and can be obtained from the normality condition: N L N e dxCd Cd L = = ∫0 0 ψ (12) The right � hand side of eq. (12) contains the total quan- tity of Cd+ ions redistributed in the sample. The term from the left side N Cd L determines the number of ions before the electric field was applied, with the uniform initial distribu- tion of the ions taken into account. Fig. 4 shows that at the potential ψ 0 = 60�80 the con- centration of mobile defects drops by 3�4 orders of magni- tude (for L = 1 cm). Cd ions are confined within a thin layer ~10L D (L D � Debye�s length, L D = 10�5 cm for N Cd  =   = 1015 cm�3, T = 300 K). Obviously, Cd+ redistribution caused by the external elec- tric field (fig. 4) can be formed by the electric field of a different nature. The capacitance of the space charge layer near the edge of the crystal is associated with the potential Ψ 0 /2. This potential may originate from a phase interface. Fig. 5 demonstrates the values of the bulk concentration of mobile Cd which can be reached by the action of the electric field on the metal � CdS interface for various metals. The values of contact barrier heights Ψ b (in kT/e units) were taken from [12]. Ψ b (in the terms used above) corresponds to Ψ 0 /2 in formula (10) and in fig. 4. Cd+ redistribution presented in fig. 5 is calculated for crystals of length L = 0.2 cm under the assumption that one face of a crystal is coated with a metal deposited thereon. 4. Conclusions The possibility is considered to clean out mobile charged defects from the bulk of a crystal by means of the electric field. Calculations are made only for the stationary limit, which can be taken as a boundary condition for the transient problem at t→ ∝. Hence, our analysis demonstrates the po- tentialities (determined by the absolute minimum of the sys- tem energy) that could be actualized by action of the electric field. The conditions for «cleaning» are most appropriate at ∆N > 0, while at ∆N < 0 the situation is opposite. The transi- tion from ∆N > 0 to ∆N < 0 could be reached using band-to- band illumination of the crystal. Experimentally, this phe- nomenon was observed in [8], where the crystal illuminated with UV light was cleaned of mobile defects over the 1/4 of the crystal length. The Schottky barrier field was found to be effective for reducing the concentration of mobile defects. Calculations were made for various contacting metals. Fig. 3. Distribution of ion concentration and potential of the elec- tric field at i/i 0 ~ 0 (capacitor). 3,0 2,5 2,0 1,5 1,0 0,5 0,0 10-3 10-2 10-1 100 10 1 10 2 10 -1 100 101 102 103 104 NCd/NCd 0 "CATHODE" N Cd /N Cd 0 |Ψ | |Ψ | (L-x)/LD N. I. Kashirina et al.: Theoretical approach to electrodiffusion... 44 ÔÊÎ, 1(1), 1998 SQO, 1(1), 1998 109 1010 1011 1012 1013 1014 1015 1010 1012 1014 1016 1018 1020 N= Cd (initial) L=0.2 cm Au (Ψb=40) Sb (Ψb=28.1) Ag (Ψb=24.2) Co (Ψb=20.4) Sn (Ψb=14.6) 109 1010 1011 1012 1013 1014 1015 1010 1012 1014 1016 1018 1020 N= Cd (initial) L=1 cm Ψ0=50 Ψ0=40 Ψ0=20 Ψ0=60 Ψ0=80 Fig. 4 and 5. Diagrams to determine the anticipated value of the final (stationary) concentration of mobile Cd ions in the bulk (N0 Cd ) for a certain value of the initial uniform concentration (N= Cd ) at various magnitudes of the external potential y 0 applied (Fig. 4 for the case of external electric field) or contact barrier potential yb (Fig. 5 for the case of Schottky barrier potential formed by the deposition of metals Sn, Co, Ag, Sb, Au [12]). The potential values are presented in kT/e units. 5. Acknowledgments The authors would like to thank Prof. N. E. Korsunskaya and Prof. N. B. Lukyanchikova for fruitful discussions and useful remarks. References 1. M. K. Sheinkman, N. E. Korsunskaya, Photochemical reactions in II-VI semiconductors. In: Physics of II-VI compounds, ed. by A. N. Georgobiany and M. K. Sheinkman (in Russian), Moscow, Nauka (1986). 2. I. V. Akimov, V. I. Korostelin, I. V. Akimova, V. I. Kozlovskiy, Yu. V. Korostelin, Proc. of Lebedev Inst., 177, p. 142 (1987). 3. I. A. Drozdova, B. Embergenov, N. E. Korsunskaya, I. V. Markevich, A. F. Singaevski, FTP (Soviet Phys. - Semicond., in Russian), 29, p. 536 (1995). 4. A. Oginskas, K. Bertulis, A. Chesnis, N. Shiktorov, Lit. Fiz. Sbornik (Lithuanian Col. Pap.), 21, p. 37 (1981). 5. I. A. Drozdova, B. Embergenov, N. E. Korsunskaya, I. V. Markevich, FTP, 27, p. 630 (1993). 6. A. Zamouche, T. Heiser, A. Mesli, Appl.Phys.Lett., 66, p. 30 (1995). 7. N. E. Korsunskaya, I. V. Markevich, T. V. Torchinskaya, M. K. Sheinkman, FTP, 13, p. 435 (1979). 8. V. V. Kislyuk, N. E. Korsunskaya, I. V. Markevich, G. S. Pekar, M. K. Sheinkman, FTP, 30, p. 884 (1996). 9. V. P. Zlomanov, and A. V. Novoselova, P-T-x Phase Diagrams of Metal- Chalcogen Systems (in Russian), Nauka Publ., Moscow (1987). 10. V. L. Bonch-Bruyevich, F. D. Kalashnikov, Physics of Semiconduc- tors (in Russian), Nauka Publ., Moscow (1977). 11. J. S. Newman, Electro-Chemical Systems, Prentice-Hall Inc., Englewood Cliffs, NJ (1973). 12. N. M. Forsyth, I. M. Dharmadasa, Z. Sobiesierski, R. H. Williams, Semicond. Sci. Technol., 4, p. 57 (1989). N0 Cd (final) N0 Cd (final) ÒÅÎÐÅÒÈ×ÍÈÉ Ï²ÄÕ²Ä ÄÎ ÅËÅÊÒÐÎÄÈÔÓDz¯ ̲ËÊÈÕ ÄÎÍÎв  ÍÀϲÂÏÐβÄÍÈÊÀÕ. I. ÑÒÀÖ²ÎÍÀÐÍÈÉ ÂÈÏÀÄÎÊ Í. ². Êàø³ð³íà, Â. Â. ʳñëþê, Ì. Ê. Øåéíêìàí ²íñòèòóò ô³çèêè íàï³âïðîâ³äíèê³â ÍÀÍ Óêðà¿íè Ðåçþìå. Äàºòüñÿ àíàë³ç ìîæëèâîñò³ ðîçïîä³ëó ðóõîìèõ òî÷êîâèõ äåôåêò³â â íàï³âïðîâ³äíèêó ï³ñëÿ 䳿 íà íüîãî åëåêòðè÷íîãî ïîëÿ äî âñòàíîâëåííÿ ñòàö³îíàðíèõ óìîâ. Ðîçãëÿäàþòüñÿ äâà ñïîñîáè ïðèêëàäàííÿ íàïðóãè: à) áåçïîñåðåäíüî äî çðàçêà, á) äî îáêëàäèíîê êîíäåíñàòîðà, ì³æ ÿêèìè ïîì³ùàºòüñÿ çðàçîê. Ìîäåëü òàêîæ ìîæíà çàñòîñîâóâàòè äëÿ åëåêòðè÷íèõ ïîë³â áóäü-ÿêî¿ ïðèðîäè � ÿê çîâí³øí³õ òàê ³ âíóòð³øí³õ, ùî âèíèêàþòü, íàïðèêëàä, íà êîíòàêò³ ìåòàë-íàï³âïðîâ³äíèê. ÒÅÎÐÅÒÈ×ÅÑÊÈÉ ÏÎÄÕÎÄ Ê ÅËÅÊÒÐÎÄÈÔÔÓÇÈÈ ÌÅËÊÈÕ ÄÎÍÎÐΠ ÏÎËÓÏÐÎÂÎÄÍÈÊÀÕ. I. ÑÒÀÖÈÎÍÀÐÍÛÉ ÑËÓ×ÀÉ Í. È. Êàøèðèíà, Â. Â. Êèñëþê, Ì. Ê. Øåéêìàí Èíñòèòóò ôèçèêè ïîëóïðîâîäíèêîâ ÍÀÍ Óêðàèíû Ïðèâîäèòñÿ àíàëèç âîçìîæíîñòè ðàñïðåäåëåíèÿ òî÷å÷íûõ äåôåêòîâ â ïîëóïðîâîäíèêå ïîñëå âîçäåéñòâèÿ íà íåãî ýëåêòðè÷åñêîãî ïîëÿ äî óñòàíîâëåíèÿ ñòàöèîíàðíûõ óñëîâèé. Ðàññìàòðèâàåòñÿ äâà ñïîñîáà ïðèëîæåíèÿ íàïðÿæåíèÿ: à) íåïîñðåäñòâåííî ê îáðàçöó, á) ê îáêëàäêàì êîíäåíñàòîðà, ìåæäó êîòîðûìè ïîìåùàåòñÿ îáðàçåö. Ìîäåëü òàêæå ïðèìåíèìà äëÿ ýëåêòðè÷åñêèõ ïîëåé ëþáîé ïðèðîäû êàê âíåøíèõ òàê è âíóòðåííèõ, âîçíèêàþùèõ, íàïðèìåð, íà êîíòàêòå ìåòàëë-ïîëóïðîâîäíèê.