ELECTRONIC DEVICES DIODES

Transcription

1 AGH NVERSTY OF SCENCE AN TECHNOLOGY M. STANSŁAWA STASZCA W KRAKOWE Faculty of Computer Science, Elelctronics an Telecommunications EPARTMENT OF ELECTRONCS ELECTRONC EVCES Piotr ziurzia, Ph.. C-3, room 413; tel , Piotr.ziurzia@agh.eu.pl OES more etails LEs varactors Zener ioes tunneling ioes EiT P Electronic evices - ioes 2 1

2 OE t is p-n junction forme an seale within the housing with contacts ANOE p-base n-base CATHOE symbol: p-n junction (metallurgical, technological) EiT P Electronic evices - ioes 3 OE N C CRRENT CRCT EXAMPLE ata: E=3V, R=10k, S =0,1pA, T=300K, ioe Looking for: =? =? E R R EiT P Electronic evices - ioes 4 2

3 OE N C CRRENT CRCT SOLTON Equation base Kirchhoff s law: The ioe current, Shockley s formula: Substitution of : Finally we can calculate: E R R EiT P Electronic evices - ioes 5 OE N C CRRENT CRCT SOLTON S =0,1pA, T=300K, ioe x OPERATNG PONT WORKNG LNE E R ata: E=3V, R=10k max = E/R =3V/10k = 0,3mA (when = 0) max = E (when = 0) R EiT P Electronic evices - ioes 6 3

4 OES YNAMC RESSTANCE i u P(, ) i u i P r u i S e T T T electrothermal potential Small-signal scheme of a ioe i u r u EiT P Electronic evices - ioes 7 OES LE B Al Ga n V C Si Ge Sn V P As Sb raiative recombination (luminescence) GaP -V AlP AlAs GaP GaAs GaSb EC S Zn EV Eg=2,26eV hv=2,2ev green EiT P Electronic evices - ioes 8 4

5 OES LE LGHT EMTTNG OE R E 0,7 2,5 EiT P Electronic evices - ioes 9 EiT P Electronic evices - ioes 10 5

6 prą ioy [ua] vs. characteristic of the P-N junction (real ioe) Lab exercise no. 2 lgi lg = 20mA 1/2n 1000 R S = 1,3 = 26mV 100 1/n lg KP0 1/2n 10 lg GR0 lg u / T 1 iffusion u T current ranges for ioes: 1 - small currents, 2 - recombination, 3 - iffusion, 4 - rift, 5 - ohm 0,1 0, napięcie [mv] i GR0 e u irs 2T u 1 0 e irs T 1 1N saturation current of minority carriers ( S ) EiT P Electronic evices - ioes 11 SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE The law of mass oes not apply: 2 np n i Carrier generation rate is not equal to the recombination rate: G R Electrical neutrality can be isrupte: q( N N p n0) A 0 0 EiT P Electronic evices - ioes 12 6

7 SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE NJECTON, EXCTRACTON NJECTON supplying carriers to the semiconuctor 2 region: np n i EXCTRACTON removing carriers from the semiconuctor region: 2 Accumulation of carriers: np n i n n0 n', p p0 p' Carriers concentrations at thermoynamic equilibrium aitional carrier concentration - excess carriers EiT P Electronic evices - ioes 13 SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE NJECTON introuces imbalance Small levels of injection : p' n n injection of holes to N n' pp small isturbance of equilibrium: injection of electrons to P quasi-inifferential state Large levels of injections: p' n n' p n p internal electric fiel n' p' EiT P Electronic evices - ioes 14 7

8 SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE GENERATON an RECOMBNATON GENERATON transition of an electron from the valence ban to the conuction one RECOMBNATON "return" transition of an electron from the conuction ban to the valence irect recombination nirect recombination: passage through the quantum states in the ban gap resulting from efects in the crystal lattice of atoms or other impurities (gol) - generation-recombination centers Surface recombination: passage through the quantum states in the ban gap corresponing to surface states the ege of crystal ( collapse in perioicity of the crystal structure) EiT P Electronic evices - ioes 15 SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE GENERATON an RECOMBNATON return to the equilibrium Equilibrium: resultant rate of recombination-generation processes : 2 V R G R Cnp, G Cn C recombination coefficient RG V mbalance: V RG C( n0 p' p0n' n' p') when: n n n, p p for a low level of isturbance (injection) we have: n' n therefore: C( n p0) ' or otherwise: th, th i 2 RG C( npn i ) V RG 1 C( n 0 p 0 ) 0 n The rate is proportional to the amount of carriers n' V RG for n: 1 for p: CN A 0 ' 0 p EiT P Electronic evices - ioes 16 0 ' p - lifetime of excess carriers the average uration of their existence in the semiconuctor 1 CN 0 8

9 ' ' SEMCONCTOR N A STATE OF THERMOYNAMC MBALANCE CARRERS CONCENTRATON at ESTABLSHE LEVEL of NJECTON or EXTRACTON injection 2 pn pn pn ( x) p 2 pn (0) t x 1 0,5 1 0,37 e 0 L P1 L P2 Per analogy, for extraction we have: ' n ' n p ( x) p ( )(1 exp( x / L p )) EiT P Electronic evices - ioes 17 X Change of the carrier concentration is a result of iffusion : in a steay state, taking into account recombination, we have : 2 pn 2 pn pn0 p x The solution with the bounary conitions : pn 0) const, pn( ) p when injection is consiere: L ' n ' n p ( x) p p p p ( n0 (0) exp( x / L p ) - iffusion way vs. characteristic of the P-N junction (going into etails) GENERATON an RECOMBNATON in EPLETON AREA for reverse bias as a result of generation in the epletion layer, the number of minority carriers rifte by the electric fiel increases electrical current uner reverse bias increases ensity of generation current: J g qgl G rate of generation, l with of epletion layer 1 ni 2 s ( N N A)( B ) After substitution: J g q 2 qnn A for asymmetric junction p + -n: N J A N ensity of saturation current: 1 2 s N an : J g J s ( B ) 2n q i p p or: J J g S N l 2n L i p G n i l S 2 2 s ( N N A)( B ) qnn A 2 i qn 1 p / N EiT P Electronic evices - ioes 18 9

10 vs. characteristic of the P-N junction (etails) GENERATON an RECOMBNATON in EPLETON AREA for reverse bias J J g S N l 2n L i p The effect of the intrinsic concentration: E g then n i an J g /J S i N For Ge we can neglect J g Eg 2kT n C NV e For Si an GaAs we can NOT neglect J g Comparison of current-voltage characteristics for reverse bias irection Figure from: W. Marciniak Przyrząy półprzewonikowe i ukłay scalone, WNT 1979 EiT P Electronic evices - ioes 19 vs. characteristic of the P-N junction (etails) GENERATON an RECOMBNATON in EPLETON AREA for forwar bias part of majority carriers iffusing through a epletion layer recombine electrical current in forwar irection ecreases ensity of recombination current: J qrl 1 ni after substitution: Jr q l exp( 2T ) 2 Jr 1 N l an: exp( 2T ) J 2 n L i p r R0 ni 2 np 2 R rate of recombination, 2 np n exp( ) l with of epletion i T layer ni R exp( 2 2 ) T Comparison of currentvoltage characteristics for forwar bias irection Figure from W. Marciniak Przyrząy półprzewonikowe i ukłay scalone, WNT 1979 EiT P Electronic evices - ioes 20 10

11 vs. characteristic of the P-N junction (etails) HGH LEVEL OF NJECTON Concentration of excess minority carriers becomes comparable to or greater than the opant concentration in the base of the junction (eg. for p + -n it is: p n N ). There are also majority carrier concentration inreases the conuctivity moulation in the base appears. Furthermore, the electric fiel occurs from the injecte charge carriers. Finally: J ~ exp( 2T ) EiT P Electronic evices - ioes 21 vs. characteristic of the P-N junction (etails) SERAL RESSTANCE With the increase in current (forwar bias) we observe an increasing impact of resistance of a semiconuctor areas in the immeiate vicinity of the junction serial resistance therefore: J r s voltage rop over a ioe voltage rop over a junction EiT P Electronic evices - ioes 22 11

12 prą ioy [ua] vs. characteristic of the P-N junction (real ioe) Lab exercise no. 2 lgi lg = 20mA 1/2n 1000 R S = 1,3 = 26mV 100 1/n lg KP0 1/2n 10 lg GR0 lg u / T 1 iffusion u T current ranges for ioes: 1 - small currents, 2 - recombination, 3 - iffusion, 4 - rift, 5 - ohm 0,1 0, napięcie [mv] i GR0 e u irs 2T u 1 0 e irs T 1 1N saturation current of minority carriers ( S ) EiT P Electronic evices - ioes 23 EiT P Electronic evices - ioes 24 12

13 CAPACTANCES N OES JNCTON CAPACTANCE Junction capacitance is create in the epletion area, therefore it ominates at reverse bias moe p Q 0 qax p N A x p0 0 x p0 l qn x n0 Charge ensity qn A n Q 0 x x n0 qax n N 2 B N A N l q N AN 2 B l q 1 2 N N 2 l with of epletion area A cross-section area of the junction A N N A in equilibrium, in the absence of external polarization Q qaxn 0N qaxp0 1 N N A N xn0 l x p0 l N A N N A N A the polarity of the external voltage VERTE EiT P Electronic evices - ioes 25 CAPACTANCES N OES JNCTON CAPACTANCE N AN Q qa N N C j A Q l A Q C u A 2 B A C j l N AN 2 B 2q How o we know it? B N N A N AN N N For junction (p + -n) NA>>N, therefore xn0 l, xp0 0, then: 1 A 2q 2 C j N 2 B conclusion: by measuring the capacitance of the junction, we can etermine the concentration of the less-ope region A C j0 m j 1 m 2 1 m 3 C j0 C 1 B C j for abrupt junctions for linear junctions B EiT P Electronic evices - ioes 26 13

14 CAPACTANCES N OES FFSON CAPACTANCE iffusion capacitance it appears when the junction is forwar biase, it results from a voltage elay against current Let s assume junction (p + -n), so: NA>>N, therefore xn0 l, xp0 0 p n p Profile of free carriers istribution Q p p p n e xn Lp The entire istribution profile of free carriers is renewe by injecting charges by the flowing current. Otherwise, this istribution profile woul isappear as a result of recombination after the perio τp the mean lifetime of holes in n-type material. Q p Q p Q p qa 0 p x x n n x n C Q p p T How o we know it? EiT P Electronic evices - ioes 27 CAPACTANCES N OES reverse polarization forwar Junction capacitance prevails C j >C t is relate to accumulation of charges in epletion area iffusion capacitance prevails C >>C j t is relate to the current flowing through the junction C j0 C j C Q p p T B C j0 C j m 1 B EiT P Electronic evices - ioes 28 14

15 EiT P Electronic evices - ioes 29 OE MOELS SYMBOLC MOELS equivalent schemes NON-LNEAR large-signal LNEAR small-signal STATC YNAMC EiT P Electronic evices - ioes 30 15

16 OE MOELS LARGE-SGNAL MOEL, STATC Shockley s formula: T ( ) e 1 S or: ( ) GR0 e r 2 S T 1 S e r T S 1 t is NON-LNEAR relationship between current an voltage r () Controlle current source (accoring to the equations above-mentione) r S r leakage resistance (for reverse bias) r S series resistance EiT P Electronic evices - ioes 31 OE MOELS LARGE-SGNAL MOEL, YNAMC ynamic phenomena are represente by: junction capacitance C j an iffusion capacitance C r () C j r S C EiT P Electronic evices - ioes 32 16

17 t OE CONTROLLE CONCTANCE i 2 2 P 2 operating point P(, ) i u i u i 1 P 2 g constant component variable component i u i u g u u g 1 i u 1 g 2 i u 2 EiT P Electronic evices - ioes 33 OE MOELS SMALL-SGNAL MOEL, LNEAR NOTE: if the voltage an ioe current are small then NON-LNEAR characteristic can be LNEARZE locally arroun the operation point i + PP i t u u = + sin(t) EiT P Electronic evices - ioes 34 17

18 OE MOELS SMALL-SGNAL MOEL, LNEAR i tangent at OP i S e u n T 1 r u i (, ) nt S nt 1/r PP u usually n = 1 an r T k k r r S moel for forwar bias EiT P Electronic evices - ioes 35 OE MOELS SMALL-SGNAL MOEL, YNAMC r C j r S r ynamic resistance r S series resistance C j junction capacitance C iffusion capacitance C limiting pulsation EiT P Electronic evices - ioes 36 gr 1 r C occurs when the voltage rop across the junction is comparable with the voltage rop on the series resistance (r S ) S j 18

19 OE MOELS SMALL-SGNAL MOEL, LNEAR (EXAMPLE) A silicon ioe operates at a current = 10mA. Calculate the static an ynamic resistances. i Static resistance: R T ynamic resistance: r 10mA 1/R 1/r PP u For a silicon ioe we can assume = 0,6V an electrothermal potential 26mV for T=300K. therefore: R = 0,6V/10mA = 60, r = 26mV/10mA = 2,6. How woul the R /r look like against? EiT P Electronic evices - ioes 37 EiT P Electronic evices - ioes 38 19

20 BREAKOWN of p-n JNCTON The suen rise in current above a certain voltage of reverse biase junction Zener breakown Avalanche breakown Thermal breakown EiT P Electronic evices - ioes 39 ZENER BREAKOWN The electric fiel in the thin epletion layer can break the covalent bon of atoms of the crystal lattice electrostatic ionization internal emission (Zener effect). E C P <0 J nu N Tunneling of electrons l 2 s ( B ) qn p + -n: N A >>N E F increase in the concentration of opants - the narrower the epletion layer E V E C E F smaller with of the potential barrier - easier tunneling of carriers J pu E V EiT P Electronic evices - ioes 40 20

21 AVALANCHE BREAKOWN The strong electric fiel accelerates the free carriers to the spee allowing the breakage of covalent bons in the lattice collision ionization avalanche multiplication. P <0 B + N The intensity of the electric fiel has to be of the orer 10 6 V/cm F p Coefficient of avalanche multiplication: F n M 1 1 BR breakown m voltage m for Si: 2 6 BR Current ensity: J 0 J M J 0 current ensity before breakown EiT P Electronic evices - ioes 41 STABLZNG OE ynamic resistance EiT P Electronic evices - ioes 42 21

22 Breakown voltage [V] BREAKOWN of p-n JNCTON Avalanche breakown Zener breakown opant concentration in the base [cm -1 ] Source: Figure 26 in Physics of Semiconuctor evices, Secon Eition, S.M. Sze, John Wiley an Sons, New York, 1981, p.101 EiT P Electronic evices - ioes 43 STABLZNG OE t uses reversible breakown of the junction (Zener an / or avalanche) Parameters: Stabilizing voltage Z (calle Zener voltage) Temperature coefficient of voltage stabilization ynamic resistance r z Maximum power issipation P max thermal resistance R th maximum junction temperature T jmax EiT P Electronic evices - ioes 44 22

23 STABLZNG OE ynamic resistance r Z Z Z ( Z, Z ) Specifies the stabilizing properties of Zener ioes - the slope of the characteristic breakown region The relationship of TWZ an the ynamic resistance against breakown voltage Figure from S. Kuta Elementy i ukłay elektroniczne, AGH 2000 EiT P Electronic evices - ioes 45 STABLZNG OE permissible power issipation P max P max etermines the maximum power that can be issipate in the ioe at a specifie temperature. sually, in atasheets, it is quote at ambient temperature T amb =25 o C P max T j max R T th amb Exceeing the maximum power of the junction most commonly causes estruction of a ioe resulting from overheating EiT P Electronic evices - ioes 46 23

24 EiT P Electronic evices - ioes 47 THERMAL BREAKOWN higher temperature increases the reverse current in junction heating an further increase in current positive feeback estruction of junction resulting from overheating EiT P Electronic evices - ioes 48 24

25 vs CHARACTERSTC NFLENCE OF TEMPERATRE Reverse bias Temperature coefficient of reverse saturation current of minority carriers : 1 0 TW 2 3 ni AT exp Eg0 / kt 0 ln T T 0 Eg0 1 Eg0 TW 0 ln A 3ln T 3 T kt T kt For silicon E g =1,21eV at T=300K we get: TW 0 15 %/K Temperature coefficient of generation-recombination current: TW 1 Eg 0 2T kt GR0 3 For silicon E g =1,21eV at T=300K we get : TW GR0 7,5 %/K The relative change of total reverse current usually is not more than 9 %/K For every 10K reverse current oubles EiT P Electronic evices - ioes 49 0 vs CHARACTERSTC NFLENCE OF TEMPERATRE Forwar bias iffusion current range, when n 1 ( = F ), then: 0 F qf exp 0 exp nt kt therefore: TW TW 0 F T F T TW FT T T TW Temperature coefficient of forwar voltage TW F F T F 0 F T F 1 T t F const nk q 3 g0 T F 2mV / K EiT P Electronic evices - ioes 50 25

26 ioe as thermometer EiT P Electronic evices - ioes 51 NFLENCE OF TEMPERATRE ON BREAKOWN VOLTAGE Zener breakown T E g tunneling Avalanche breakown T vibration amplitue of atoms the probability of collisions free path kinetic energy of the carriers avalanche multiplication avalanche EiT P Electronic evices - ioes 52 26

27 NFLENCE OF TEMPERATRE ON BREAKOWN VOLTAGE Temperature coefficient of breakown voltage TW Z 1 Z T Z efines the relative change in the breakown against temperature EiT P Electronic evices - ioes 53 NFLENCE OF TEMPERATRE ON BREAKOWN VOLTAGE Zener breakown Avalanche breakown T T TW Z < 0 TW Z > 0 EiT P Electronic evices - ioes 54 27

28 vs CHARACTERSTC NFLENCE OF TEMPERATRE T -2mV/K T for each 10K the current oubles EiT P Electronic evices - ioes 55 EiT P Electronic evices - ioes 56 28

29 TNNELNG OE Tunneling ioe is create by a junction forme with two egenerate semiconuctors p ++ n ++. egenerate semiconuctor is one in which the opant concentration level is approaching the atom concentration of the material. p n EF EC E EV EiT P Electronic evices - ioes 57 TNNELNG OE r<0 -r EiT P Electronic evices - ioes 58 29

30 EiT P Electronic evices - ioes 59 OES N ELECTRONC CRCTS SGNAL FORMNG CRCTS PEAK ETECTOR OE GATES VOLTAGE CLPPER RECTFERS VOLTAGE MLTPLER CHARGE PMPS EiT P Electronic evices - ioes 60 30

31 APPLCATONS OF OES SMPLE RECTFER Low ripple amplitue: When following conition is fulfille : i RLC L >> T t E L E L RL CL T t t Electronic evices - ioes 61 APPLCATONS OF OES FLL-WAVE RECTFER E T E t CL L RL t EiT P Electronic evices - ioes 62 31

32 APPLCATONS OF OES SGNAL FORMNG CRCT N N R1 OT t 1 4 m1 m2 m3 OT m4 2 R2 5 t 3 R3 6 m1: current flows through (R1) m1=1 m2: current flows through (R1, 1, R2) m2=(r2)/(r1+r2) m3: current flows through (R1, 1, 2, R2, R3) m3=(r2 R3)/(R1+R2 R3) R4 m4: current flows through (R1, 1, 2, 3, R2, R3, R4) m4=(r2 R3 R4)/(R1+R2 R3 R4) EiT P Electronic evices - ioes 63 APPLCATONS OF OES VOLTAGE CLPPER N OT N OT +3.0V +0.7V t -0.7V -3.0V N 4.3V 6.8V OT N OT +10.0V +5.0V t -7.5V -10.0V EiT P Electronic evices - ioes 64 32

33 RESET APPLCATONS OF OES PEAK ETECTOR in C V R V RZ in V RESET t By means of peak etector C voltmeter can measure amplitue of variable waveforms. Capacitor C is charge via a ioe, a large voltmeter internal resistance prevents its rapi ischarge. Short-circuit with RESET button ischarges capacitor with very small time constant τ=rzc thus, new measurements can be taken. EiT P Electronic evices - ioes 65 APPLCATONS OF OES AM EMOLATON EiT P Electronic evices - ioes 66 33

34 APPLCATONS OF OES PARAMETRC VOLTAGE REGLATOR N R Z Parametric voltage regulator without a loa N Z OT eal characteristic of a Zener ioe OT Z Z Z N Z T Z N EiT P Electronic evices - ioes 67 APPLCATONS OF OES PARAMETRC VOLTAGE REGLATOR N R Z L Parametric voltage regulator with a loa N Z RL OT eal characteristic of a Zener ioe OT Z R L N R R L Z R Z 1 RL P P N WEZ Z Z R R L Z P T N EiT P Electronic evices - ioes 68 34

35 APPLCATONS OF OES PARAMETRC VOLTAGE REGLATOR R Effect of changes in input voltage to the output voltage, when RL=const u N N u in Z RL u OT OT u out Real characteristic of a Zener ioe uout uout Z P(N, OT) Z T R L N R R L P r R Z 1 RL uin un EiT P Electronic evices - ioes 69 APPLCATONS OF OES PARAMETRC VOLTAGE REGLATOR Effect of changes in input voltage to the output voltage R u in r u out u out r u r R in EiT P Electronic evices - ioes 70 35

36 APPLCATONS OF OES PARAMETRC VOLTAGE REGLATOR R Effect of changes in loa resistance RL on the output voltage at WE=const. u N const. Z RL u OT OT u out Real characteristic of a Zener ioe uot Z? P r T RL EiT P Electronic evices - ioes 71 METAL-SEMCONCTOR JNCTON Combination of the silicon ie with the element terminals (leas) it shoul be low resistance not influencing on C vs characteristic it is in some cases there may appear a junction EiT P Electronic evices - ioes 72 36

37 M-S JNCTON (METAL-SEMCONCTOR) Work function W the energy require to transfer an electron from the Fermi level to infinity (W - W F ) Electron affinity - the work function from the minimum energy level in the conuction ban E C energy of electron in vacuum S W S W M E C E F E i E F E V metal semiconuctor n-type EiT P Electronic evices - ioes 73 M-S JNCTON B barrier potential q B q 0 E C E F 0 contact potential E V metal semiconuctor n-type From Poissona eq. 2 S 0 S qn Rectifying junction Schottky ioe S EiT P Electronic evices - ioes 74 37

38 M-S JNCTON n case of external polarization : S 2 S ( 0 ) qn q B tunneling E C E F N S n+ n E V tunneling can occur - the loss of rectifying properties metal S semiconuctor n-type to make the ohmic contact, there must be sufficient opants concentration EiT P Electronic evices - ioes 75 SWTCHNG THE OE YNAMC EFFECTS E M -ER E EF F tt EF Δ R ts tf t t t current switching: R r r s M EF ER R tr for m=1/2 1,58RC j0 EF 0.7V EF 0.7V F R r R F eg t r r s 1,125 RC j0 for m=1/3 F R i E tr RC j ln RC j ln RC j E 0.7V f EF>>0.7V an EF=ER R u ER 0.7V R R rise time tr t s tt ln 1 storage time F R t off t t s f t f 2. 2RC j falling time EiT P Electronic evices - ioes 76 38