Monograph On Semi Conductor Diodes

Transcription

1 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 Moograh O Semi Coductor Diodes Christo Aath, Assistat Professor, Deartmet of ECE, Fracis Xavier Egieerig College, Tiruelveli, Idia PN juctio diode, Curret Equatios, Diffusio ad drift curret desities, forward ad reverse bias characteristics, Switchig characteristics. 1.1 PN JUNCTION DIODE: juctio diode is formed by blocks of semicoductor material : tye material ad tye material regio : holes majority carriers electros regio : electros miority carriers majority carriers holes miority carriers 40

2 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 * Holes from -side diffuse across the juctio ad recombie with electros i - side. * Free electros that cross the juctio create ositive ios (because the atom loses oe electro) o -side. * Diffusio of holes i -material creates egative ios (because the atom gais oe hole) * Sice egative ios are created o -side of juctio, regio close to juctio acquires egative charge. * Similarly ositive ios created o -side gives ositive charge ear the juctio. Shae of Charge desity( ) deeds o doig level of diode. * As these charges build u, a oit is reached where total egative charge i - regio reels diffusio of electros ito -regio ad diffusio stos. At this oit, ositive ios o -side ad egative ios o -side are immobile. * Regio ear the juctio is called Deletio regio or sace charge regio or trasitio regio (Width of deletio regio = 1 m) * Sice there are may ositive charges ad may egative charges o oosite sides of juctio, a electric field is formed. * Exteral eergy must be alied to move a electro through electric field. Exteral eergy deeds o Potetial differece of electric field across deletio regio. * Potetial differece required to move electros through electric field is called Barrier otetial (V 0 ) [V 0 = 0.3V for Ge ad V 0 = 0.7V for Si]

3 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 * Whe egative termial is coected to -side ad ositive termial is coected to -side, the device is said to be REVERSE BIASED P - + N Iitial width of the deletio layer Barrier otetial for ubiased juctio Barrier otetial reduced by forward bias otetial Deletio layer decreased after forward bias Fig 1.3 Forward Biased Juctio * Whe FORWARD BIAS is alied to Juctio, holes i -side are reelled by ositive termial of battery ad flow towards juctio. * Similarly electros i -side are reelled by egative termials of battery ad move towards juctio. * These electros ad holes recombie with ios ear boudary ad reduce deletio layer width BARRIER POTENTIAL REDUCTION * If alied voltage is further icreased, barrier otetial disaears ad charge carriers ca easily flow across juctio. 4

4 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 * Collisio ad geeratio of carriers results i large amout of reverse curret called as REVERSE BREAKDOWN. Reverse breakdow occurs at articular reverse voltage for -juctio kow as REVERSE BREAKDOWN VOLTAGE. 1.3 CHARACTERISTICS OF JUNCTION - DIODE (V- I CHARACTERISTICS) [FORWARD AND REVERSE CHARACTERISTICS] X (A) CIRCUIT DIAGRAM TO OBTAIN FORWARD CHARACTERISTICS OF DIODE: D Fig 1.5.CIRCUIT DIAGRAM TO OBTAIN FORWARD CHARACTERISTICS OF DIODE 43

5 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 * Resistor limits forward curret to a value that will ot heat the diode. * Ammeter is coected to measure diode curret I D ad voltmeter measures voltage across it. * By varyig dc Voltage source, voltage V D ad curret I D through diode ca be measured. * Whe alied voltage is 0, Voltage across diode remais 0 o forward curret. Whe alied voltage is icreased gradually, forward curret ad voltage across diode gradually icreases. Further more, Voltage across diode icreases raidly to barrier otetial ad forward curret icreases raidly. Christo Aath et al.[1] discussed about riciles of Semicoductors which forms the basis of Electroic Devices ad Comoets. Christo Aath et al. [] discussed about Imroved Particle Swarm Otimizatio. The fuzzy filter based o article swarm otimizatio is used to remove the high desity image imulse oise, which occur durig the trasmissio, data acquisitio ad rocessig. The roosed system has a fuzzy filter which has the arallel fuzzy iferece mechaism, fuzzy mea rocess, ad a fuzzy comositio rocess. I articular, by usig o-referece Q metric, the article swarm otimizatio learig is sufficiet to otimize the arameter ecessitated by the article swarm otimizatio based fuzzy filter, therefore the roosed fuzzy filter ca coe with article situatio where the assumtio of existece of groud-truth referece does ot hold. The mergig of the article swarm otimizatio with the fuzzy filter hels to build a auto tuig mechaism for the fuzzy filter without ay rior kowledge regardig the oise ad the true image. Thus the referece measures are ot eed for removig the oise ad i restorig the image. The fial outut image (Restored image) cofirm that the fuzzy filter based o article swarm otimizatio attai the excellet quality of restored images i term of eak sigal-to-oise ratio, mea absolute error ad mea square error eve whe the oise rate is above 0.5 ad without havig ay referece measures. Christo Aath et al.[3] reseted a brief outlie o Electroic Devices ad Circuits which forms the basis of the Clamers ad Diodes. 44

6 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 (D)CALCULATION OF DEPLETION WIDTH: d V = E = dv E = + Fig 1.8 a) JUNCTION DIODE b) CHARGE DENSITY IN DEPLETION REGION c) ELECTRIC FIELD INTENSITY IN DEPLETION REGION d) ELECTROSTATIC POTENTIAL IN DEPLETION REGION * Charge desity is egative to left of juctio ad ositive to right of juctio. * Electric field i deletio regio establishes otetial barrier V which obstructs flow

7 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 of electros ad holes across juctio. No. of holes i -side = No.of accetor ios = N A No.of electros i -side = No.of door ios = N D

8 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 V = qn Ax TO FIND C AND D : + Cx + D; 4, C ad D itegratio costats Boudary coditios : At x = 0 ; V = 0 ad at x x, V= dv =0 At x = 0, qn x V = A + Cx + D ε V= D x=0 0 = 0 +D (QBy boudary coditio1, At x = 0, V= 0) D = 0 at x=x dv qn = A x + C costat = qn A x + C At x = x, dv = 0 (By boudary coditio) 0 = qn A x P + C C = qn A x P qn x A qn A x x 4 V = + 0 qn x qn x V = A A x qn x V = A ( xx )

9 ISSN (ONLINE) : X ISSN (PRINT) : X Available olie at Iteratioal Joural of Advaced Research i Biology, Ecology, Sciece ad Techology (IJARBEST) Vol. 1, Issue 3, Jue 015 q = N N D x (1+ ) ε D N A x = V O V = O N A qn N qn (N + N ) D 1+ D D A D N A x = V o N D Similarly qn A ( N A + N D ) Deletio width = x + x 1/ V N V N O A O D = + qn D ( N A + N D ) qn A ( N A + N D ) 1/ 1 / 1/ V N N O A D = + q ( N A + N D ) N D N A (V 1/ ) (N + N ) = O A D 1/ A N A N D q 1/ (N + N D ) 1 / 1/ 0 A D V (N + N Deletio width = qn A N D ) 1/ 1/ X

10 UNIT - I SEMI CONDUCTOR DIODE V 0 = q I regio, ositio of Fermi level E FP = E i - KT Similarly E F =E i +KT l i Sice Fermi level is costat, E FP = E F =E F E KT l N A i E 0 i l N A i N D E + KT l N D = i E 0 = E i - E i KT l N l N A D = + i i N E = KT l N A D 0 i E KT N N 0 = = A D V 0 l q q i i V 0 = V T l N A N D Assumig comlete ioizatio, 0 = N A 0 = N D i V 0 = V T l N A N D i V =V l 0 T 0 0 i

11 Curret Total Curret I I Hole Curret Electro Curret x = 0 I I electro diffusio curret electro diffusio curret Distace Fig.1.1. CURRENT COMPONENTS Cosider forward biased juctio. By alied voltage, holes are ijected ito - side ad electros ito -side of diode. L et ' (x) icrease i miority carrier cocetratio above equilibrium 0 hole cocetratio i -side at equilibrium decrease i hole cocetratio due to recombiatio. ' (x) = - 0 Cotiuity Equatio states that Rate of chage of hole cocetratio = Sum of all icrease i hole cocetratio For steady state, d = 0 1 dj dt q d = 0 dt 0 = 0 1 dj q 1 dj = ( 0 ) q dj = q( 0 ) 1

12 k = 0 At x =0 ' (0) = k 1 k 1 = ' (0) x / L P '( x) = '(0) e + 0 Diffusio curret, I (x) = AJ = x / L ' (0) P e = ( (x)- ) e x / L P 3 0 d = A(-q D ) d = -q AD ( ) 4 We have ' (x) = - 0 = ' (x)+ 0 d d' = (x) 4 I ( x) = q A D d ' ( x ) d = qad P [( (x) ) 0 )e x / L ] I ( x ) = qad ' (0)e L (Qfrom 3) x / L I (x) = qad L ' (0)e x / L I (x) = AqD P ( (x) x/ L )e (Q from 3) 0 L P Miority diffusio curret crossig juctio at x = 0 is

13 l (0) = 1 (V V ) 0 0 V T (0) = o e (V 0 V ) /V T 5 By Law of Juctio, V 0 = V T l 0 0 V 0 = l V T 0 0 e V 0 /V T = = 0 e V 0 / VT Subs 6 i 5, 6 (0) = We kow that 0 = e 0 e (0) = 0 e V /V T V 0 /V T (V 0 V)/V T (V 0 V 0 +V ) /V T AqD I (0) = L '(0) AqD = ( (0) 0 ) L AqD = L ( 0 e V /V T 0 ) I (0) = AqD 0 L (e V /VT I (0) = AqD L 0 (e 1) V /VT 1)

14 = for silico For forward bias voltage, Curret equatio is I = I o e V /VT For reverse bias voltage, Curret equatio is Note: VV I= I T 0 (e 1) From this V /V I = I T 0 (e 1) D D I = Aq + [e V /V T 1] i L N P D L N A I D D J = = q i + [e V /V T 1] A L P N L D N A J = q D D + V /V [e T 1] i D N D D N A J = q 1 D P + D 1 [e V /V T 1] i P N D N A J = q i N D J = q i N A D (e V / VT D 1) (e V / 1) X PROBLEMS: Cosider silico juctio at T= 300K so that i = cm -3.Assume -tye doig is cm -3 ad assume forward bias of 0.60V is alied to juctio. Calculate miority carrier hole cocetratio at the edge of sace charge regio. Solutio: Give T = 300K 10 i = cm N d = 1 10 cm -3

15 D = 10cm /s 10 i = cm = 0 = 5 10 s r = 11.7 SOLUTION: 16 Give : N a =N d =10 cm , D =5 10 m/s, D =10 10 m/s 10 i = cm -3, o = 0 = s, r = 11.7, T=300K D q J i 0 = + N D ( ) ( ) = J 0 = A / cm PROBLEM:3 q i N A D Door cocetratio such that J =0A/cm ad J =5A/cm at V a =0.65V, D =5cm /s, J = q D i (e V /V T 1) N A Accetor cocetratio 15-3 N A = cm Similarly hole diffusio curret desity, X Cosider silico juctio diode at T =300K. Obtai Accetor cocetratio ad D =10cm /s, 0 = 0 =5 10 s, i = cm -3 Solutio: Give : T = 300K, J =0 A/cm, J =5A/cm, V =0.65V, D o = o =5 10 s, i = Electro diffusio curret desity, cm -3 =5cm /s, D =10cm /s, a = ( )( ) 5 ex 1 N A q D J = N i (e V /VT 1) D

16 By Diode curret equatio, V/V T I = I 0 (e 1) di 1 = I 0 dv ev /VT V T dv = di V T I o e V /VT We have I = I 0 (e V /V T -1) 1 I = I 0 e V /V T -I 0 I+I 0 =I 0 e V /V T Subs i1 dv = V T di I + I 0 For forward bias I >> I 0, V T r f I X 1.4 DRIFT CURRENT DENSITYAND DIFFUSION CURRENT DENSITIES (May/Jue Marks, May /Jue marks) DRIFT CURRENT AND DRIFT CURRENT DENSITY: (I &I P ) (J & J ) * Whe small electric field is alied across semicoductor bar, holes move i the directio of alied field whereas electros move i directio oosite to that of alied field. * Combied effect of movemet of holes ad electros costitute electric curret which is kow as DRIFT CURRENT. Drift curret for electros I = Aq E Amere Drift curret for holes I = Aq E Ameres Drift curret desity due to free electros J = A I Drift curret desity due to holes J = A where o. of free electros /cm 3 o. of free holes / cm 3 I = q E A/cm = q E A/cm X

17 * If vertical lie y-y is draw, desity of holes o left side of vertical lie >Right side * As x, Cocetratio of imurities i semicoductor. DIFFUSION CURRENT DENSITY DUE TO HOLES, J = qd d D = diffusio costat for holes (m /sec) J = qd d Similarly D = diffusio costat for electros (m /sec) J d ( QCocetratio gradiet is egative as x icreases) TOTAL CURRENT DENSITY IN SEMICONDUCTOR: Total curret desity = Drift curret desity + Diffusio curret desity For - tye, J = q E + ( q D d ) J = q E q D Similarly for -tye semi coductor, J = q E q D TRANSITION OR SPACE CHARGE CAPACITANCE C T (Nov /Dec Marks, May/Jue Marks) d d X * Whe diode is reverse biased, holes i -side ad electros i -side drift away from the juctio Thickess of deletio regio icreases Caacitace effect is exerieced across deletio regio. * Width of deletio regio icreases with icreasig reverse bias voltage, So Caacitare varies with reverse bias. * The Caacitace due to deletio layer is called Deletio caacitace or Trasitio caacitace (C T )

18 * I ste graded juctio, cocetratio i ad sides are uiform ad trasitio from to side is abrut at the juctio * W Width of deletio regio o -side W Width of deletio regio o -side N A W P = N D W N A Accetor cocetratio N D Door cocetratio N A >>N D W <<W W W Relatio betwee otetial ad charge cofiguratio d V = 1 = qn D dv We kow that E = dv = ( from 1) Q x E = x 0 E = x + C At x = W, E=0 (Boudary coditio) 0 = ρ W + C ε C = ρ W ε E = x W

19 1 = qn D W dw dv j 1 = qn DW dw dv j dw dv = 6 j qn D W Subs 6 i 5, dq dv = qn D A qn W D dq A = dv W C = T dq A = dv W X DIFFUSION CAPACITANCE: (Nov /Dec Marks, Nov /Dec Marks, Nov /Dec Marks, May /Jue Marks, May / Jue Marks, Nov /Dec Marks) * Diffusio of miority carriers o both sides of juctios gives rise to Diffusio Caacitace. * Carriers get accumulated ear the juctio before they get diffused ad recombie with majority carriers. So holes i -regio ad electros i -regio are searated by thi deletio layer which leads to Caacitace called Diffusio Caacitace. Diffusio Caacitace, C D = dq dv dq = τdi where τ mea lifetime of holes ad electros di C D = dv = g (Qcoductace g = di dv ) = r

20 MINORITY CARRIER DENSITY DISTRIBUTION: * Whe exteral voltage is alied to forward biased juctio, desity of miority carriers is large. * Whe exteral voltage is alied to reverse biased juctio, desity of miority carrier dimiishes to zero Reverse saturatio curret (I 0 ) is small * Diode wll coduct oly whe miority carrier desity ( - 0 or - 0 ) has droed to zero ad curret will be determied by exteral resistace i the diode circuit. STORAGE AND TRANSITION TIMES: * Iut voltage V i =V F is alied to the circuit below: Fig 1.17 DIODE - CIRCUIT * For a log time, voltage remais the same (uto t 1 ). R L is assumed to be large Curret i V F / R L I F * At time t=t 1, iut voltage reverses abrutly ad becomes V = -V R. So curret reverses i V R I ad becomes R R util time t=t (show i (a)) L

21 * Time iterval which elases betwee t ad the time whe diode has omially recovered is called trasitio time (t t ) * REVERSE RECOVERY TIME (t rr ) is the time iterval from curret reversal at t = t 1 util diode has recovered to certai extet (as show i(c)) DIODE APPLICATIONS: 1. Rectifiers i dc ower sulies. Cliers i wave shaig circuits 3. Clamers i TV receivers 4. Voltage doublers i CRT 5. Comarators X PROBLEM : 4 16 Cosider silico juctio at T=300 K, N a =N d = 10 cm -3 10, i = cm -3, D = 5cm /s, = = s, D =10cm /s, =11.7 with a alied forward bias voltage o o r V a =0.65V. Fid electric field itesity required to roduce give majority carrier drift curret. Assume =1350cm /V-s GIVEN: N a = N d = 10 cm, D =5cm /s,d =10cm /s, i = cm, 0 = 0 =5 10 s, r =11.7, T=300K, V a =0.65V, =1350cm /V-s J 0 = q i N D D + q i N A D 1 D 1 D = q i + N N D A = J 0 = A / cm Total curret desity, J = J 0 (ex (V/V T ) -1) + ( ) = ( ) [ex ] 0.06 J = 3.9 A/cm Sice is give,

22 Reverse bias saturatio curret for Juctio diode is 1 A at 300ºK. Determie its ac resistace at 50 mv forward bias. SOLUTION: GIVEN: η=1(ge), V =6mV, I = A, V= 50mV, T=300K T 0 r = V T I VT = V / V I e T 0-6 I 0 =1A. I = A, = (Si) = e / 6 10 a.c. resistace r = Ω PROBLEM 7 : (QI = I 0 e V /VT = ( e V / ) 3 X for forward bias) If reverse saturatio curret i juctio silico diode is 1A, fid alied Voltage for forward curret of 0.5 A. SOLUTION: GIVEN: I = I ( e V /V T -1) = ( e V / ) = ( e V / 5 10 ) V l(501) = V 6.16 = Alied voltage, V = 0.33V X

23 For what voltage will the reverse curret i juctio diode reach 80% of its saturatio value at room temerature. Solutio : For Si, = ad room temerature =300K I = 80% of I 0 I =-0.8I 0 (Qit is reverse curret) I = I V /V T 0 (e 1) V T = 6mV at T = 300K -0.8 I 0 = I 0 (e 1) V / I + I = I (e V / ) I 0 = I 0 (e V / 5 10 ) 3 0. = (e V / 5 10 ) V l 0. = V = Voltage V = mv (As diode is reverse biased, voltage is egative) PROBLEM :10 = 475m /V sec X A secime of metal -tye silico has resistivity 0.0 Ωcm at 300ºK. Assume =475m / V- sec, = er cm 3 Fid cocetratio of holes ad electros. i SOLUTION: GIVEN = 0.0 Ω cm = Ω m 10 i = /cm 3 = /m 3 For -tye silico,

24 REFERENCES [1] Christo Aath, S.Esakki Rajavel, S.Allwi Devaraj, P.Kaa. "Electroic Devices.", ACES Publishers, Tiruelveli, Idia, ISBN: , Volume,December 014, : [] Christo Aath, Vivek.T, Selvakumar.S., Sakthi Kaa.S., Sakara Narayaa.D, Imulse Noise Removal usig Imroved Particle Swarm Otimizatio, Iteratioal Joural of Advaced Research i Electroics ad Commuicatio Egieerig (IJARECE), Volume 3, Issue 4, Aril 014, [3] Christo Aath, W.Stali Jacob, P.Jeifer Darlig Rosita. "A Brief Outlie O ELECTRONIC DEVICES & CIRCUITS., ACES Publishers, Tiruelveli, Idia, ISBN: , Volume 3,Aril 016, :