1 ugimeenin sha. jeal Electnenies : the bronch oh _ ee iG Which deals ho Cunnent conduction Hhmough a Vaccum on ‘gas on semi Conducton is Known as Electvenies Electnowics pevice + An electric device tw tat mw —Sctremies device Which connent Slows Hrnovgh a Vaccum on ges on. Semi Condueton. Applications a) Electne | —PPications the cs Electmonie devices ane capable of Performing the following — functions i) Reed; newt ss the convensian oe ae Witte dee ‘S called Rectification Electnonic devices can Covent ace Powen in te die Power. with Very high efficiency. this dec Sopply can be Used fon. changing Stonage batteries | field Supply of Ae Generatons ete. lv Electnonic + . device isi the (i) Amplification :- the -precess eh ais 4 stmength of a Weak Signal is Known as | Amplification lex. Radio's, Televisiowsi) ap ex v ey ete W) Genenation Electronic devices can de Ppowen Ww to ae Pewen el any Freprency, | then performing this fonction , they ane Electnonie device Contno® Electnonie devices find ude plications tn automatic Contnol. Speed gl a moton , Voltage across a Convent Known as oscillatons v os Electnenia device t| +———— electese a - Electneyi \) conversion of tight _in to 5 ; tei ty. this devices can Convent LUght Ww to electricity conversion af Light iu to electricity ts Knbuow | ex oe alanms ete os photo Electricity. vi) convensiow op Electricity inte hag nt is Convent €lectnicity in Electnonic devices can to hight Thy — Valvable Property in vbilised im television and Madan.genenatly matenials ane classified in te 3 types i) rsvlatens ii) Metats iii) Semiconductons Tmsvlatens '- A veny Peon Conducton of ead is catled On Trsvlaten gt weed, glass , Diamond , Mica ete Wi) teletalie tee on eee ene eeducton is a metal - EX! copper , Alluminiud “ete tii) Semi Cemducton'- a matenial whose emductvity Les between that ol Conductons and insvlatens is called Semi Condvctons. Ex. Silicon and = genmanivm Stmuctone al an Atom i- —> all the protons and weutnems ane bound together, at the centre ot an atom , which is called nucleus while all the electrons ane alle , uclevs oy anovnd whe WM u e different] — the electnons one annanged wa th nucleus onbits ot fixed distonces fre the hell can > Fn genensl , an onbit on a she n + electrons of 2m , Contain a maximyer numbe he. the namber oo} the = she! whene “Wl lL associated — Fach Shell has energy leve—> Closen the ice eee ceeees reece reece tguey it W bound to the nucleus ond Ppesesses Loewen enengy Level — the ovtenmest shell WwW Catled valence shett and +he Clectnems tv Hin Shell ane called Valence electrons —> the valence electrons navelving in the outer most shell ane said te be having highest enengy level —> the amoent qh energy negued to extmact the valence electnen from He ovten shell & | veng less [> pn electnem which ig net Subjected to the fence 4 attnachon 4 the wuclevs W Called a4 free electnon- Such free electnems ane basically Respomible to the flow a Gunmen, — mone the humberr 4 free electrons betten in the Comavctyity o} the metal. Enenqy band au LH A moteniol Can be placed into insvlatons, | conductors and Semi conductors depending upon its enengy band Stnuctune the tee band diagnam consists o} thnee bands () vatence band @) condvetion band (3) Forbidden band@) Valence band - The valence electnons possess highest erengy level when such electnons Form the covalent bends dve to the cevpling between emen, | Valence electrons of adjacent atom, te a3 4 levels band formed due to Merging Cf eee A: associated with the Valence electrons: je: electnoy in the last Shell ts” called +he valence band (2) condvetion band -- valence electrons form the COncuctiOn Ess a covalent bend and ane not free, bot when centain enengs, is impanted te theen they become! free - the enengs band fonmed due to menging of emengy Levels associated with the free electron is cailed Condvehm band unden honmal Conditos, the Conducthon band is empty and once emengy is Impanted . band the valence electnons jump from valence to Condvction band and become fee (8) Fonbidden band :- while Jemping from valence band to Garin Geer) th Grog aa Jam emengy §eP the emengy gap which present Sepanating 4he conduction band and thé Valence band is called fenbidden band orn forbidden enengy Gap—— | Tnsolatons ‘- the emengy band odnae OS | insolaten ts shown “uw Figuae below. Enengy conductor Band Forbidden | t Band Lt valence Band Ld the valence band is Folly filled and Conduction band is almost empty and fenbidden gap 1s mene appronimately about 7ev Fon a diamond , the fonbidden gap is aboot 6ev | Conduction is impessible in insvlatons even by applying additimmal enengy the nesistvity af insulators is af the onden oh tot ohm-meten. Condvetons | the emengy band ee 4 condvetons 1% shown im fgune below: Condvcho Bond ZZ, valence cB Bond—— FE Hene the Valence band and Condueten bond Figure AS aw band can oven lap each otven as Shown in Resvit the electnons in the valence { easily move in to the Cenductan band +t? of the cadar a 16 From: 0 bond diagram make conduction easily. the resistivity by (3) Semi Condvesons -- the Semi Conductons | eo} Semi Conductons is Shown in Figure below energy Conduction Band 1s almost filled and Rene the valance band ene. condvetion band is almost empty. THe Smengs GaP between Valence band and Condvetion band ts very Smatl ond if abovt 1ev- seni Condveton ib the mesistivity oe} ee me aden aoe | Hence smallen electric field iy neguiaed €O posh the electnons from the valence band to the Condeetion — band: Ak lew teemperatuae , the Valance band is Completely fell and Conduction band is Completely empty+ therefore at low temperatures the ”| Howeven even at oem tempeaature, seme el the valence Electmons acqitne theamal enenqy greater. thom Eg to ovencome forbidden enengy gap and jvmp in to the Conduction band to make the Conduction pessible- Hence as the tempenatuae increases the conductivity o} Semiconducton mMaeases te nesistance decreases. therefore semi Conductors have negative Resistance tempeaatvae Coopficient » At otk, the forbidden gap for Genmanivm 1s Eg = ov8s ev ond fon — Silicon (si) ts 2) ey the fenbidden emenay ger depends on temperature At Room temp ie Book Fon 4@ Che eae Fon = tev 4 commonty used Semi Conductons thene one mony semi Conductors available, bor Veny few gt them have a pnactical application im electnonics. the two mest frepentyy used jmatenials ane Genmanium and silicon. st & because the enengy neguised to bheak Hein covalent bond (ie «the enengy depuised to selease on electmon from tein. valence bends) 4 Very } | Small being o-t2ev fox Ge and lev fon si |D genmonium Cae) —_—_— The atomic number eo) ge is 32. thenefone ie has 32 protons and 32 electrons: Two electnons ane im the finst onbit ; eight electrons a the Second , 18 elecinons im the thind ond 4 electrons ma the — ovten (on) valence ombit Ft is clean that §@€ atem has Valence electnons ie toy shown tn igre) a tetnavalent element. gat is Fg (9) fig te) Fg tb). shows how the Vanious Germanium atoms ane hed through eo-valent bonds. As the} atoms ane annanged ia am ondenty pattern , | §e has ory staline struc bone . icon (si) t= Silicon is an element Oa iw most ep the common Hoeeks. _ Sond ts silicon di onide. and this is chemically nedvced| |to siveow which & 100% pone fon use as a Semi conductan.the atomic number of silicon is i: Thenefone tt has MF pmotons and 1% electnons. Two electnons ane in j the finst onbit, ejgnt electnons im the second enbit ond foon electnons im the sfdiha onbit. This 15 Shown in figl> below. St clean that silicon atom has fovr@ Valance electnons ie. it is a tetmavalent element £9 &)- Aye) Fgle) shows how Vanievs Silicon atoms ane hetd thnovgh Co-valent bonds: Like MMONTUN , 3b Silicon atoms ane also annanged in on ees monnen» These fone sicon has reapptalime Structure, | Classification oe] semi Conducton matenials Semi Conductor matenials one Classified im to Gee, shes Tmbninsie semi Conductons & Extrinsic Semi Condvcrons » ) Entainsie Semi Condveton - A pune form a) semi- Conductor matenial is Known “as intrinsic semi conducton materialwhen thene ane four electnons iw the qutenmost onbit, the Semi Conducton matenial WW nefecced to as pone on intninsic Semi Cenduc ton. Em pune Semi Conducton , the numben of jholes is Equal to the Number of free electrons Even at Room tempenatune, Some of valence electnons may acgsine Sufficient enengsy [to enten the Conduction band to fonm face Clect¥oy onden the inf lwence eL electric field , these electyons constitutes the electnic cunnent the comment dve to the movement of | free electnons im the Cenduction band is an electron connent | | A missing electnon in the Valance band leaves + a Vacant Space +thene , which +g Known as a hole. evden the influence of Clecte field, the cumnent dve to the movement g holes im the valance bond is a hole connent- | thenefone the €lectron as wett as hele cConnent together constitutes the total gonnent in on ‘mtninsic Semi Conductor. Extninsic Semi Conducton :- the imtninsie semi Condveton has Little Connent CondveHon capability at moom tempeaatune. To be vseful im nds = 2electronic devices , the pone Semi Conductor must | be atkened so as to Si mificontly imesease tts Conducting prepenties. Tha is achieved by adding @ Smatl amovnt 4} suitable imponity to a Semi Conducton. It is tken catled im puratey on satninsic semiconductor: i so is called Extninsicl Doped Semiconducton matenial ¢ impone) Sei Conducton. the process o} adding Small amoont a} imponities | | te the pone form of Semi Gmdveton, in onden +o increase the conductivity of semi Conductor is -2oping - Known as Depending Spon type a) impumities, thene ane two types a) extninsic Semi Conductons () N- type (a) P- type G@) N= type Semi Conductor t= when a Small amount of pentavalent mponity soch as Ansenie( As) , Antimony (sb), ] Phosphonovs , Bismuth eke is added to pone fonm a} Semi Conductor, it is Known ag n-type semi Conducton these pentavalent impomittes ane alse called “donor. imprity atoms, because they donate on provide free e@lectnons to the Semi Conductor Crystalfig: Fommation 1 covalent bonds in N- type semiConducton one deman impunity atom donates one free electnon wm N- type matenial. thene fone free electmons ane majority change canniens in N-type Semi Conductons- the Following Points may be noted Cone folly Jmany new free elecknons ana produced by the addition of pentavalent impunity 2) thenmal emengy at Teen temperatose still generates a few Clectnen - hole pains + Howeven) fre Momben g fiee electnons provided by the Pentavalent impunity fan exceeds the homben of holes» Zt is due to this predominance oh electrons oven holes that it & called n-type semiconductor (rn stands for Negative). Hene | holes ane the Minonity Canniensh- type Conductivity i- the connent Conduction hm on on type sem Conducton is Predominantly by free electmang. When Potential difference in Conductor, the free applied acaess eo type Seer electnons (donated by trponity) in the Ceystal will be dixected teiwands the posikve terminal, | Comshtu& electnic Connent- So tha type o condockvity ts called hype Conductivity x Th. R aa e donan imponity atem donates ome electro) to the crystal and becomes * positive len” | thenefone n-type Semi Conducton — cosists | fee electnoms and ~ positive len’ Positive | — Free Electney tem P- + SPE Semi Condveton cendveton when a Small amoont of trivalent | impont & Soch imi | P y as Boren, Aluminium » Tndiven, Gallium is added to a Pore semi Gwrducton,Te is called P-type Seni Conducton. these Enivalent imponities ane also called “Acceptor imponities ”. ee hole in ome Accepton tenponity creates a P-type matenial, thene fone +he holes ane majonity change canniens. £19: Formation OL covalent bends in P-type Semi Conductons. Hene fourth bed is incomplete A being Short ol cme electnoy . this missing electnem ig catled AL a hole: thene fone for cach Gaeta atom Gavedy one, anoles ig cieated a rei oe en q Aativm provides — millions of holes. = Howeven | thene ane a few Conduction band électmons dve to thenmat enengy associated with Room tempenatune. bot the holes ane fan exceeds the number of _electnons: because of thispre dominance a holes oven free Electrons , this | tape al semicenducton is called P-type Semi Conductor. (r Stands for positive ) Potype condve. ee Hole ee . negative accepton ion the Cunnent temdoction im P-type Semi Corclucten| is predominantly by holes. when petenhal difference is applied to the P-type Semi Conductor, the holes ane shifted from one Covalent bend to anothen. As the holes ane Positively changed , they ane dinectad towards the. negative temminal , constituting hole Cumnent- so tin type of Comdverui ty As catled P-type Dl xx the acceptor impunity atom is short of ome electmom, f and becomes a wegarive im thenefone P-type Semi Condutton Consists oh holes and Megative ions -— T and minonity Canniens :— Fate Electaens Majonit 8 Cmajoniiy Grniw) In N- type Semi Conduction. the majority Cantons one Elections aud the winoniay Conn one hole’ He = holes. Cminonity Grriend “yy N-type hotles (majonity Im P-type Semi Comdueton_ carnieu) Majonity Camniens ane holes and the ed Gnnien ane the Cleatmens - electrons Cminenity @uiew) fg) P- type 7 ™ a piece o Semi Comdvcton matenial , ip ome half i$ doped by p-type Imponity and the other half is doped by N- type impunity. a PN junction is fonmed. ls the plane dividing the’ two halves on zoney is called PN junction . J PH donetion > P-type semi Cmducton Consists of both holes | and Negative aecepton ions ( the acceptor impurty atom Us shont of ome electron and becomes a negative tom)> the N- +ype Semi Conducton Consists oh both electrons Pesitive denon tom ( the denon imponity and atom demates me electnon ond becomes a positve ion) \> Hene n-type material has a high Coeentnakon | of free electrons while P-type matenial has high cemcentmakon of hole $ le thenefone at the Jonction , thene is a tendency | fon the face digfuse oven to the €lectnons to P- side and holes to the N-Side- thin process 4 called diffusion | > As. the free lectmems = move aAnoss the jonction | from N-type to P-type, positive uncevened. Hence a positive n- Side of the dovon ies ane a is built om the jonction —> Ae the Same Hime, the free electmons exdes the siemction and on coven the hegatve acceptor ions by filliwg tm the holes . Hence a net negative | change is established ow. P-side ol the jonckeyn > Now positive change om oN-side Repets holes | fo cress fom P-type to ne type, and nega tive change om P- side Nepels fred electnons to h-type to P-type. thus set op against fonthen movement of This iy enten faom bannien ig change Cannions called potenHal bannien, on bannien Potentialom junction . bannien (Vo) + axe TH depletion Layer > Bannien. Potenhat indicates the amount ol) Voltreg.e te be applied acioss the PN junction to nestant the flow aq eleetmous and holes acsoss the joncken > the bannion potential i expaeMed um Volts. rtg value i» called the height of Hae barvnion. > the Magnitode op the bamnrion potenkal varies with doping levels and tempenatune > the potential bannion com be increased on de : eneased “by applying an external voltage Veeeetchet. Potontioler Ua ess 1.5 oppronimately OV for Si and ov for Ge at aste | > Tmside the petewtial bannion, thene is a Positive, change om n-side ond negative ae om P- side. this hegiom iy called depletion pegion on Space change Deane > the thickness of thin degion w of me onden of we cm Cem = 1 mieum)Hele —_ @ iow ®) generar shape of change distribotion. ©) tlectrie field Be fon holes tn tue depletion region fon electaons in te depletion Hegion Figuie: Aceeptom __| (4) amnion potential (e) Bannion potenmat P (oom oeeT electron S00 OC po SG OOOO: oe depletion <9 veegion , ' | pehainge densit: Ne ! 1 — = Distance from ' denetion \ A Elecitnic field imtewi. € i Field inten ity — Diskance from ; june tion 1 A ben! baninion potenNal pside ' | - ' 1 % 1 4 Distance, hole for , tH ' : : ' Jonerion tole ' banister Potential foro \ tf Ss distance from 1 : ' : 1 1 demetion . Fermation of PN JunctionPN Jonchen as a Diode :~ EE —™——— aga | ometiom Wo. trate const tutes a ieee j Permits the . €asy flow 4 connent im - ome direction} ond nestnicts the flow +} dunnent in opposite direction . ‘ ECS Se) eee et Sey ty Figure below. Auede carhede pf the P-type and n-type Regions ane Referred to as Anode and Cathode Cee the Ammo iw the Yoobot dicates the disection of easien Conventional = cunnent flow openatien eL PN junction piede + © Fonwand Bias + => when the positive tenminal. op the botteny ts comected 0 the P-type and the negative +e nminat of the oa) ts connected to n-type ot Pa jonction diode, then the bias “is said ty be Fonwond bias A PN jJoncKho with fonwand bias is shown in Figue berow aa+ _ 1 PN Gonetion with Vv Fonmand Bias -> when the PN jonction is fommand biased , as long as the applied voltage is tess than the bannion potential thene cannot be omy Condection ~> when the applied Vortoge hecomes mone than the | barnion potential, the negative tenminal of battery poshes the free electnons against bannion potential from A to Pp negion similanty positive tenminal pushes the oles from p to MV region thus holes get nepetled by the positive tenminal and cross the junction against the bannios Potental , électroy gets Repelled by the negative tenminal and cross the jonction against the bonnion petential. thus the | applied Voltage ovencomes the bannion potential. this neduces the width of the depletion region > As fonwand voltage is increased, at a panticulan| Vole the depletion region becomes vd much NannovSuch that leaye number oh major ty change Cannier, can cmess the junction ond these majority Canaiers con tnavel anound the closed eincvit ond constitute a Cumnent ‘called fonwand cumnent > the fonwand potential at which the Potential bamminn acnoss the junction is Completely eliminated and allows the cumnent to flow through the Jenction is called cot-inw voltage (on) threshold Voleage of PN jometiom diade. Boe eg ae —> the Cokin oeede fon Si is OrF¥ @) Revense Bias '- when the posihve +tenminal. of the battery is commected td the N type and the negative terminal of the. a is comnected to the P-type of the PN junction Diode, then bias Said to be Revense Bias. A PN jonetion with Aevense Bias Ww shown iM Figure below: To‘= pepleaan Se 2 2 2 Fig: PN jometion with ‘Revene Bias —> when the PN jonctom is nevense biased the negative tenmimal attmacts the holes in the P-sagion | owe from the jumetiom, the positive tenminal Attnocks the free electmons im He ie egies from the — jenctim. > No chomge Cannien iB able 48 cnoss the junction 7 AS electmons and holes both move away fiom the junction, the depletion Region widens. Hence the nesvitant potential bannion ts drcacased which Prevents the flow of majority Comniens tx both dinec tions > thenefone , Hreone tically no Connent shovid flow im the extemal Cincvit. Bot im pnoctice, ao od | Small cunnemt of the onden of a few micno Ampenes flows onden neVense biased Condition. —> Electnons forming covalent bends ce the semi conde| j 7 7 fatoms in the Pond ON type Magions may obsonb Sefficient enengy from heat and Light to cause breaking of Seme Covalent bends. Hence electro — hole pains ane continually produced im both the P| Cee “> onden the mevense bias Cemditiow the Khenmalty | generated holes im the Caden ane altaacted | towands the Acie tenminal of the battery and the! ClecknonS wm the N- region one alttnacted towands | the positive tenmimal of the batteny i> conseprently the mimonity Camniens ie. electnons m the P-nagiow , and holes in the n-megion, wanden| oven to the junction and flow towands their mojonity cert sat giving mise to a smal mevense comment. this comment is Known as hevense Satunation Cunnent Ip > the Magnitude gf Hevense Satonation cunnent mainly depends pen junction +tempenatune. becawe the Major Source of omimoni ty Consdens is thermally bnoken Co-valent bends — atnendy majonity fice Electrons from N-~ Side ane Positive patie a towands neg terminal of batteng » the newly Libenated electrons will also join with tase majoni ty electnovs> Thun a lange number, of free electnons ane fonmed which is commonly catted as ani | avalanche ef free electnons: thin leads £0 the bacakdou af the jonetion leading to veny lange jevense Curent) jones break qhe nevense vortage at which the gyneKow own | down ceeons is Known as Avalanche break d bow of Jouctim | o | sf the hole concentnations at the edges eo} the depletion dian ane Fo ond Ry in the P and N materials reamed , oma if the bamnion potential across this depletion lagen is Vg the % fs Rew ? a | thy is bottzman helation of Kinetic gs theory — > Fern an opencineited pn Jonction {| ® pp = ro) Pu Pro, Ve Vo (Vo is comtact Potential) S| the above values in 0 we get v Pro = Fao € —®> emsiden a fonwand biased Jonction with — applied Voltage v, then the baxsvion, Voltage Va is decreased from. its equilibrium value Vo by the amount Vv ©) Vg = \o-V. P the hole Concentnation _ ovt the P-negim is Constant ond eqal to thenmal equilibrium value on B= Po: the hole Concentration Vanies with distonce in to the n-side- Ak the edge q depletion loyen , the distance from “the Junction %=0 Pa = Palo) Fon this case bolkgman Relation is (Vo- Pro = Pde” O/ve —-> © Combining &y © ond 2 @ we get . Vr = Wott lv Vo-v Pro @ | = ls) @ Ny eqysivalent of — y = [ ras) Pro eT] —> @ tempenatore this boondany conditioy is called the baw of | gonetion- Simi m only for @lectnons cocentnation om P- side “Po el¥s —> © np(o) the abeve eqpiation @) indicates that the hole concentnation Palo) at the Junchem onden fonwand biased ramAthima 18 amankon dann Le Hremmal eatiilihsive value ProsDiode cunnent Equation \- | Fnom the law of Jonction , we have v lod) = Pro elit —@O where | Fucod = hole concentmation at the edge of che deplehe, megion in M-type matental under fonward Based — Comaitioy fee Pao = hole concentmation at the _ qt the deple tion Region in n-type material onder open cimevited Condition Vo = agpliea Volkoge Vz = Veit eqpivalent of tempenatune whe Prenence between we Comcentnations at the Gunetion Under biased and unbiased condition is catled injected on excess concentnation denoted os P 6) Palo) = Plc) - hy —+® using 40 w %@® Bi Co) = Pro ot no Bia) tk (eM _,) —-®6 NPo (ehr_.) —& Simitenty Np (0)Concentration, Pa Distance Junction the hole cunnent cnossing the junction from P-side to n-side is given by - AG Pp &, Co)” Tp, (0) = AERO _.@ uD —LULmrmUmrmr—C~S~rt~t~s——S crossing the junction | from n-side to P-Side is given by Inp(o) = Ay Dn Nelo) Ly —@ ] Cness Section of junction Comstant fon holes | where A= anea of Dp = Diffusion Dn = diffLsion constant fon electnons Lp = Diffusion Length fon holes Diffusion Length fon electnons using @ ond @ epations im ‘e7's © and © [ame total comment rat the Junction is givenI= Ip,Ce) + Inp Co) = Ad Pale) 4 44 Pn Nplo) Lp — Ly | te ALDP Pro Pe Npo (er ') io Ly y | > Ts m (e_,) —+@ | whene 1, - (5% Pp Pro + A&Pn “Po| _ Revense Lp in Satunation cConment the eqation @ is the nequined expnession fon diode comment: this equetion is denived without Consideni the carnien genenation and recombination im the depletion Region - SE we comsiden the genenation ond Recombination of camniens in the depletion the generat eqatiom of the diode comment is appmonimately Wve by ; Ving Tol e -1) —~ whene I = diede . comnent fee dicde nevense Satonation connent at Neem temp V = External vottage applied to the diode N= a ceomstant (1 for Ge ond 2 fen si J s— voit eqppivalent of temp ie thermal vottoge n600 ' -23 k= Beltgman's comstant (r3aex 6 3/k)= 19 T= chenge of the electmon = 1601 x16 Te T= tempenatune of the diode junction (?k) elt celica = Volt -Ampene Chanactenistics (va chanactenisties ) O) v-T chanactenistics im Fonwand bias Condition >t —> when a fonwand bias Voltage is applied to Oo PN jenetion diode, below the cot-iw voltage VR, the diede with not conduct and the connont Flowing is veny Small Practically this Comment is assumed te be Zeno > The diodes itt have a cot-in volta, eon threshold Voltage Va, below which eonnent is Very Small , Beyond Vg, the connent nises very Fapidiy > Ve is opprenima tely O2V for ge and o6y fon st => AS the forwand biased voltage Vp is Greater than =the cot-in Voltage Vz, the potential bannion Ocnoss the junction is completely eUminated and the eumnent nises veny apialy> he vet ch cenisti emactenistics onden fonwand biased condition is shown im figure below: Te (ma) e > st ae oav os > vz Cv) @) v-xX cho A actenistics in “Reve Xe —— lense biased Condition '— Tp - + VR when a PN Junction diede is Nevense biased, the negative teeny | atoceo. ce heles in the P- Region owoy fnem the junction: the positive tenminal attnacts the free etectnonus 19 n-Region atsay from the junction No change Carmen is able to Cross the junction. As electrons and holes both move away : 4 jegion widens: from the junction, the depletion 4 as depletion Region widens , bannito%t Potential acnoss the junction also iIncaeases: The polanities oo) bannien potential ane Same As thaton of the opplied vorbege Heweven a small Revense connent catled Hevense Satunotion comnent Ig flems acnoss the denctione duos ce | eg oy Te of minority Change Canniens Genoss the Junction Revense Satunation Cunnent is very sau of the onden eof = fem — micno ampenes fon Ge and eu hanoampenes. fon si Pn junction diode. Pe J the Genenakion of minority change Cannieng depends on the tempenatune Melons 3} the mevense bias and hot ™m the applied nevense bias Voltage is incaeased beyond certain Limit the junction breaks down lows end a veny large Tevense — cunnent £ the v-r chanactenistics unden nevense 2 . i (cs biased condition fen a Pn junction diede ¢ Shown in Fgrre below (Revense Satunation comment) To Ve ¢—____1_- . ; Ie (pa)o the complete vr chonactenisties of a PN diode (Fonmand bias ond Revense bias) fon beth Ge ane Si ane shown tm figuse belo 5, (remeen connemt) z Py, (fonsand | Crevense cate vottage) verrage) ov) Trg (Revense connent) Tempenotune dependence of V-r chanactenistics t- peiuses ebemaened Mee Shanactenistics the wise in tempenature increases the Gerenation of electnen- hole pains im semi Conductons and inereaseg thein cemdvetivity. as a nesoit the cunnent trmough the PN junction diode tacneases with tempenatune as given by the diode Connent equation. . ref e!r -\} HH the mevense satunatien comment To ol diode increases approrimate ly 7 percent /% fon both 4@ and si.Revense sarunation Connent appronimarery doubles fon every loc Rise in tempenatune. Hence Sf the kempenatone is increased at fied velkege » the comment I increases Te Cae the connent I to its original valve, the voltage Vv has to be meduced- St is foond Rhat at Room tempenatune fer either germanium av on silicon = @ -2.5 mv [2% in onden +o ar p Wel comment 7s ato ct conctont) olla) maintain At oom tempenatune ie at Zook , the Valve of bannion Me eda on evot in voltoge is aboot o3v fon g@ and oFV fon Si. the bannion voltage is tempenatone dependent and it decreases by amv/ec fer beth Ge ond St this fact ono be expnessed in mathematical form which is given by (a-wWhe Teo = Tey x 2 whene Lo, = Satenatien Comment — e) dhe diode at tempenatvre = Ty Tor = Satunation connent of the diode at tempenatune Tr jee Shows the effect of increased tempenatune on the Chanactenistic comve qi aJa PN jonetion di A ge diede can 75°e and a Si | YR | Cvetts) Preblem : Satunation connent Solution given To = He thenefone the Sat roe | Ton = 75 BA ok tempenatene ode. be used upto a maximum of diode to a maximum af 8% te (pa) i Effect of tempematune om the diode chanactenistis 1 a silicon diode has a Satunation Connent of ab Oo Ke To 2 76 KIS fA ak Ty = BOCK. So T= a9e ( Be0k~ 293°%) | ok = race onation comment at fook is | _ gt W/o re xio® ¥ Qf"? - 29) fro 763M Boo kK: Caleviateam the Vp (volts)Problem : A silicon diode hos a neyense sSatunation Connent of F12 na at noom tempenatune of &F° C+ calculate tS fonwand cumnent if it is fomwond biased = | | with a voltage of FV | solwtio? given data | Io = Tete xteta yYrorRy a ———LE vp - KD. ee sees ee any 4 1600 11600 rr comment eqration “avy 1 eee ( e ao) 712 x10 (Te o-026) | rz sma PROBLEM - A Ge diode has a Satunation connent of na at ace: Find i€$ cunnent when it is fonwand biased by O4V: Find the cunnent in the game diode when the tempenatune nises to nove, solution! Given data Fon ge diode Q=t To) = | ha = TA T= QC = QO+2FB = 293° rr ——re? Veoav | rz (eM _,) ote Be 69 Co /osconsy ) Tos 4:8ma Ta = then r= ? Ton w/e] ey da - eee ky toga ee cia nea oe Ae ot, SNe’ uo+ 243 = 383K vy = 282 = e033 600 y v. ze te ( ef-s) on want (S100) _,) 7 Preble the diode Comnent iS oemaA; when the applied vertage is #Oemv and gomq when the opplied veitege is Seo mv petermine Q Assvme KT 2 asmv yd ; y selvtion? the diede cunnent =F = ze (eM -1) _ 4oo ob x13 = To [ fe = ) es neglecting 1)Simita: -. se2 oe my 20x16 = to ( er ) agten simplifying Ney Diode Resistance :- pl G1) Fonwand _nesistance of a diode | the nesistance offered by the aiode in fonwand biased Conditim is catted fontwand mesistance + The fonuand nesistance is defined in two ways G) HE Static om De fonwond nesistance (Rk) Gi) Dynamic om nc fonwand nesistance (7p) ve Cv) Fonwand chanactenisties ef a dicde G) static on pe fonwand nesistance :- | | the static on ve fonwand nesistance Rp tS defined as the natio of the De voreoge applied acnoss the PN junchow to the De connent Slowing thnovgh the PN Junction : Fonwand de voltage 7 ony point € ae ~ 0c Fonwand dc cunnent —____ |i) Dynamic en Ac fomwand Resistance '- the mesistance offened by the fonditions is Pn jonch om onden Ac called See om ac fonwand nesistance ond is denoted by AE => the negistance is defined as the Recipnecal of the slope ef the v-T Chamactenistics dv le ape ay the dynamic wesistamce is net a Censtant bot depends i upon the operating voitage. From the diode Cunnent eqpation r= ro( eo lwr -:) Digfenentiating the , we have abeve equation une VY) we get » Sts to( or av y = fin el dv Vr a —Lrrrrt——— av Vr Fon a fenwand bias | T77 Te and ag is given | ‘ | approximately by dv ow NY> the dynamic nesistance vanies invensely with connent.| 3 Bt neem tempenatone and fon Q= ng = ASE phene ZT Bw im ma. then fe em C= hy ohms (nL) Fon a fenwand cunnent of Rema , the dynamic Jesistance is I a LrrC—s—S—SseN AV = - apse SL = 7 fF = ar 4z/av Slope a) fenwand chanactenista: > Genenalty the valve oe} my is veny mai —r—r—r————U—C—C——C—CCCCE aegion (2) Revense Resistance Of a disde :- —> the mesistance offened by the dicde in | . « ——_ Ve (Revense Voltage) Revense fig: Revense chanactenisties rq, ( ) R | comment op a diode (ua) the nevense Resistance ig defmed in two Ww (i) Static on ve Mevense Resistance (Rr) ) djnamie on AC Mevense nesistance Can) -r G) Static om mevense nesistance CRr) tm : the static nevense esistance Fr is defined as the Ratio of applied nevense De voltage to the stevense Satvnation Connent (Ze) slowing the PN Junction. applied ‘Revense de voltage 08 “wevense Satvnatoy Connent OR Cat point By thnovgh Dynamic nevense MNesistance (an) + The neyense Sc cee nesistance Fn is defined as the fiatio of iwmcremental chawge im the nevense voltage applied te ehe connespendi Oo PP ore change in the nevense Connent an AVR chonge iv mevense Voltage In = = ate change iw’ mevense Cunnent Problem | A PN junction diede has a Mevense satunation connent of 3oHA at a +tempenatune of 1as°e. At the Same tempenatune find the dynamic Resistance fon o2V bias im fonwand and nevense dinection Solvtio : Given data Sl son! se lomea) += este = tas $293 = 398K vz o2y a Bees Fou Ge =) Vr = py Cen a LUrrC—~—S 1600calculate the dynamic fonwand of Pr Jenetion silicon oasv at Te 3edk with given Te= 248 Solvtim: aiven data To = 2 PA at To3e0K vz o96V Vy = 26mv To ( clays -0) we hove re neglecting oo7 we get y fe a diffenenmaring tome voltage wv) y, v ees olay dv Ur dt Se te Ne fe a=) dv a = T _ dt oh aay vr [se al the values ] we ge : Ag = 336 ay ag a1. SE 2 Bo 9 v5 \ My av vy oe Tn = Problem : and evense jesistance| diode when the applied voltage is| Fomoond Mg 4M 2 UM Yas e resistance oe Te noe Be 2exiw3 82/ta x 2bxe3 ) yo = ———- e 2xlo é Ke = aaah Fon wtevense sesistance &, use Vz ~o25V - Ur > i e Jaye ( After Sobstitohug | z a al values ) An = 30gMHa Proplem : the voltage ponece | ee silicon cicde: ab | toes! temp of goook is oY, when ama Cunnent flows thnogh it : a SL the verbage vucaeases 40 OF5V. Calevlate the diede | cunnent asseming Yr = 26my- Setotion! Given data veeFV, => fox Si, Vpc2émv., T= 2ma- Now I= To (evr = ») aften Sobstitvting all Values we get Ty = 28m x107 A | Mew New veltag e vie oFsY v, \ after sobstitel Lr ) 2D T= 523mAa [oHag an vueIdeal vensvs practical diode | xdeat_diode + — a ———S since fon an ideal dicde thene ig no banrion potential, thus any Sma fernwand bias voltage causes Gmduction thnoygh the | device |2) the fonwand Resistance ts Zeno | 3) the Aevense Resistance is finite A”) the diede readily Condvets when” forwand biased and it bleexs Condvction when nevense biased: 5) the mevense Satunation cunnent To is Zeno 6 the ideal diode acts as a fast acting electyonie| switch V3 Re on joe 1) thene is a potential bannion across the junction, | | Practical Di ond this must be ovencome befene the diede con condvet + 2) the cot-in veltege on thneshold Voltage is oppronimabely o2v fon G@ ond oév fon Si- 3) the fonwand nesistance is in the ange of few tens of ohms ) the nevense mesistance is tm the Range of be ohms -a | 5) tm fomoand bias Condition, when the bias voltage | is mene than the — Cot-in veitoge , the diede | conducts - | 6) the diode doeswit Conduct when nevense biased However a Small Aevense Satunation cunnent flows acnoss the junetio in the Range o Rano amps fon si diode and micnoamps fon Ge diode. 3) the diode also acts as a fast acting Electnonic Switch Diode _eqprivalent cinevits '- | an equivalent cincvit ty a Combinatioy nepnesent of elements property chosen to best EP " the actual tenminal chanactenisties of de view Tn a panticvlan openating region > aA Node is Aeplaced by % model with & | battery eqpivalent to Cot-in cee of a diode, | the fonwand mesistance ef a diode in Senies | with an ideal dicde. > the piece wise Lnean equivalent cinevit gb | diode is shown in figuee elon: Fonwand Tdea\ nesistance diode - Apso, Since fom mest applications, be ignored = Companed withResistance of then elements of the Network > thenefone the Simplified eqpivelent cimcuit is as Shown im figune below | a | vp Ideal diode > Asuming Vy=z0 ond Mpzo , the eqyivelent Cimevit becemes the cinevit model for on Ideal diode! o—p>f-— Ideal diode | 5 |} > Tn fonwand biased Condition the ideal diede acts as Shont Cinevit | eDe > eee Ghent cet onden fonwcand bias —> TH Kevense bias condition the ideal diode acts oS open ext: etr- = & open ekt Unden Revense bias [Diode eqivalent cinevits/ models | v-E chanactenisties \- | [sxe] Tyre Medel ahanacteni sties | Piece wise pee tp MT rmaan | oT modet ier gee oleeas vp | Simplified a a ort} Model __ | Vato, Mgzo, An =00 ST yy Vp 5 Teal modek a Vy =o, MESO, MEO VpBreak down Mechanisms Ua a Diode °- > When the diode is nevense biased, for A Smart Serr——-———————_—__— LB and almost constant at To — Bok when Revense voltage increases beyond Centai, Valve, lange diode cunnent flows , thin is catted break down of diede and connesponding vettage is called Revense breakdown voltage of diede — thene ane two distinee mechanisms dve to which the breakdown may occon in the diode , these ane J) Avalanche break down 2 Zenen breacdown. \) Avalanche bneax deton '- > The avalanche break down occons in ghey doped diedes —> As Me applied Revense biased voltage ts imereased , the velocity and hence the Kinematic energy Che = Lm) of thermally genenated change z conniens incneases + — Sf Such change Canriens cotloide againsé on electnon invetved in Covalent bond and cAeakes | ew change canniens. — > these Secondary particles ane also accelenated| Ond -pamicipate in collisions that genenates new electnon —hele pains: This Phenomenon ty Kvown as | Avalanche multiplication.> the multiplication facten due to avalanche effect is given by ) “BaP whene PT = cannien multiplication factor Me "= CmPinical constant, which depends on the lattice matenial and Cannion type | fen n-type Silicon neh for P.type silicon nea V= applied Revenge 7) Vep = Revense break down voltoge — > De to this avalanche Cffect the jonction is Said 40 be in bneak down and the Connent stants waeneasing eared > the diodes having Revense break down Voltage Grecsten than 6Y shows the avalanche Mechanism of break down (2) zenen bneak down !- —> the Zenen break down occuns in nea doped | diodes [7 Fen heavily doped diodes, the depletion Region width is small—> vnden Hevense bias Conditions , the electnic field acness the depletion legen 7 veny intense. ay eL covalent bends due ts intense electnic field acnoss the nannow depletion nagion and Gorenating Lange hum ber, of electrons is called Zenen effect’, —> these genenated electnens Cemstitute a Ven \ J bange cunment and the mechanism is called Zemen bneakdown | the diodes hoviwg Mevense bneak down Voltage less thon Sv Shows the Zenen mechanism of bneak down Figune : Showing Zenen. ond Avalanche bneakdowns Tempenatune dependence of Bneak down Voltoges In coy doped diodes, the depletion negion | \ width is Veny Smalt- the applied voltage Produces toan electric field which is very intense. Tm such a case, af tempenatune ineneases, valence €leetnons acqine high enengy leyets and it is Cay fon the applied ee fo poll Such electnons from covalent bends te make them free. thus fon Smal Voltage ak kighen tempenatune break down cecuns+ —> thus the bneak down voltage decreases as the tempenatune incneases fon Zenen bneak down. the | Zemen breakdown has “negative tempenature Co -ef ficient” > im doped diodes , the Width of the depletion layer is laoge and field intensity is lew. the breakdown Possibility is because gl avalanche effect. > In ‘seen a case, if tempenatume imeneases , the Vibnations of atoms im the cnystat imeneases + the ineninsic holes and electnons hove less a tomy impamt Sufficient enengy between the collisions due to Vibmations, to Stamt the Cannien multiplication: Thos voltage mest be tuereased te cause the breakdown - so at Wghen tempanatone , highen break- ~ down ee e is al . —> thus the break down eae tacreases as the kempematome tacseases fon avalanche break down the avalewehe break down has a Si tempenatune coeegicient.ee PN diode applications — An ideal PN Junction diode is a two terminal Polanity Sensitive device that has Zeno Hesistance when ik is fomwand biased and infinite nesistance When Revense biased. Dve to this chomactenistic the diode finds a mumben of applications as follows ) Rectifiens in dc powen supplies 2) Switch in digital logic cimevit$ vsed in Computens. 3 Stamping networks used as de nestonen ia tv Receivens and voltage multipliers ” cUPPing Cincvits used as wave shaping Cinevits Used im Computens, fadans , nadie and Ty Neceivens 8) Demodvlation Cdetecton) cincvits > The Same PN junction with diffenent doping Concentmation finds special applications as fotlows ) vetectons (PIN photo diode) in optical Communication cinevits- 2 Zemen disdes in Voltage Ragulatons 3) Vanacton disdes in aud Sections of Aadio and TV meceivens Leo's in digital displays S) LASER diodes in optical Communication. a LULULrLrrrC—C~—t— Oscillator at Micnowove frequenciesZENER Diode when the nevense Voltage teaches breakdown voltage ua Nommal PN junction diede, the cunnent throw the junction and the Pewen dissipated at the junction will be high - Such an openation is destnuctive and the | diode gets domaged > wWhene as diode can be designed with adequate Pewen dissipation capabilities to openate tw the bneatedown negion. me Sech a diode is Known as Zenen diode > zemen diede is heavily doped thon the ondimany diode. — Symbol ft Zemen diede is as showy in Hgerne — berow Chamactenistics of a Zenen diede is > The v-r Shown da figuie betew Te (ma)Fnom the VI chanectenistics of the zenen diode shown in abeve Figore , it is found that the openation of ——”——C onden fonwand biased condition —> wwhene ag vunden Revenge biased Condition, breakdown of the junction occuns: the break down voltage depends open the amount of doping. Sf the dicde ts heavily deped depletion layer wit be EWin amd Consequentty break. ~eewn cccons at Lowen mevense voltoge ond fumthen the. break down Voltage ts Shanp+ Eysivatemt cimevit of Zenen diode! cra . Fig too? Zener ig! Practigat ge) i deal equivalent iod + oe Eyrivalent cincoit Cineuit Applications of zenen diode :- The vaniovs applicatioms ef zenen disde ane DAs a voltage negulating element tn Voltage negolatons a) Im Vanious Protecting cincvits 3) Fn Zemen Limitens ies cUpping cimevits which ane Used Fe clip off the unwanted pention of the Voltage wave foneTonnet Diode! —> the temnet diode is a thin junction diode, wenden fonwand bias Condition it exhibits Cee nesistance. this maxes the tvunet diode useful for oscillations on amplification —> Tm Conventional, PN Diede is doped to have Imponity atoms Ga the Concentnation of | Pant in 10% then the width of the depletion layen ts oF the onden of S5micnem — Bot nh temnet diode the Lnpomity emeentnation is greatyy imeneased to | pant in io then the SB. Th depletion loyen usidth Neduces to 10 device chanactenisties get Complete ly changed - > this diode otitiges the phenomenon called tonnell 4 and hence’ @ the disde is nefenned | as Tonnel diede |» Tonner diede is also called ‘Esakr diode | Tennelling phenomenmm = —-> The width of the junction bansionm Varies eed as the Squane moot of the. impunity eencentnation: That is if the Concentnation of imponity atom is greet ineneased, the bannion width ‘w' Reduces 4aA pantice must have on ener atleast eqrat to the height of the potential bamnion in onden te enoss oven the junction —> Roweven if the banmion is extmemely thin, then electnon instead of cnossing even the junctiom bonnion the electmen may penetnate thnough the bernion. This behavioon exhibited by the electnom to the applied potential is gatved “gvnneling’ and hence the diede iS called as “tunnel diode! VI chanac nistics i- Resistance Ir t t Region figune - VI chanactenistics of Tunnel diode > the heavily doped tunnet dicde nesvits in a thin depletion layer SO as to penmit tunnelling to oceun > the vr chanactenisties of 8 typieat germanivey tunnel diode is Shown tu "above Figure ee from the Figure , 3} a $Sma\l fonwand bias voltage is applied’ the cumment nisesShanply and meaches he peak Cumnent Zp point (A) = As the fonwand bias is iucaeased above this Point (a), the fonwand cunnent drops and continues to drop unl a point B is Reached: This point is the | vatag vettoge on vatley cornent (Lv) > the -tunnet diode exlibits megative nesistance chomactenisties seen between the peak Comment Ip and minimum Value Ty Cyattey connent), « > the peak cumnent Ip depends m the SiG > agten the Valley point is Reached funthen imenease in inpot ved lncneases the Curnent veny Rapidly as PN junction diode Explanation of VI chanactenistics on the basis of ‘emelting theon 22 _Enengy band diagram of Tonnel diode} the Fownetting Phenomenon is explained in tenms of the erengy band diegram of the matenial used. Im p- type Mateniat , dve to heava doping thene 1s | creased Concentnation of holes in the valance band £8 (condvttion band ) cB ere Eq | Forbidden 5! N-type L erengy gap Osacccce ©202c000 eoco oo 008 7 v VB Cvatance band) * mengy bond diagnam of two types o} Silicen.| Similanty in n- type the Concentration of electron Jis mene iu tenduction band - when P and n type Materials ane joined tegethen then the de lever diagram is as Shown iu figone Ca) 1, elecenens ' . No Fig() TH no fomwand bias is applied (shown iw figunels) thene is Rough alignment of thein mespective Valance and conduction bands+ The emengy levels of holes tn P region ane sughtly oot of alignment: Gie-akeve ) with the enengy Levels. eo} Cendvetom etectroms in N region flows across the ef the junction. thus no Connent junction . P-type N-type () sman fomsand bias Gi) Foul tunneling ig (ec) when a Smatt fenisond voltage Cosy) is opplied, the enengy bands Move opwand: DUE to this motion | | ce enengy levels of n-megion Netative to those of P - megion,the electnons im the Conduction band mom ‘nH’ side jost enoss the bannion in the Valence band of 'P) side because the two ame in Cxack Alignment. At this stage electnons tunnels through the depletion negion with the velocity of light and gives nise te lenge comment. this tonmelting eonnent Heaches a Maximum Value Tp at a fonwand bias Vp- P-type n-type ns eae acer — peptetion T Region ce ) bias increased! @ tonmenting Stopped Aften the peak point i the applied voteage is imeneased , the Conment stants decreasing because ane enengy levels ef N region Say So high thes too bonds ane ovt of alignment: Bn His case tunnelling is Stepped os shown ‘w gure @) the comment heaches the minimers valve (called valley comment) when the two bonds one totally ovt of alignment at a fenwond bias W (called | vattey vertage) . Ak a bias veltage wy, the Eumnerling és completely Stopped Fon voltages gnreaten than W , the Cunnent Stises agoiw because oe) injection cumnents in an ea PN juneKon diodeTennelling ts much fasten than & normal eee Thin to Switch ON and oFF much enables a tunnelt dicde fasten than on ondinany diode valent cinevit ef tunnel Tonnet diode Symbol revit Gathode ee | (1 cS) Rs Ga -Rn Anode, h Speed Switch diede (s vsed as an oltna enden o} ns on PS 1b Tenner with switching speed of’ the 2. AS logic Memony eee device 3 As mienewave oscillator # In Meladation gscillaton cinevit 5 AS ow amplifier. Avantages : 1 Lew noise & Ease of openation 3 High Speed 4 low Power Disadvantages : v voltoge Range oven which ik Can be apenated is iv on less a Being a two terminal device, thene is no isolation cincvit- the input and — ovtput betweenRECTIFIERS AND FILTERS PN junction as a rectifier Halfwave Rectifier Fullwave Rectifier Bridge Rectifier Harmonic components in a Rectifier circuits Inductor filter Capacitor filter Zener diode as a Voltage Regulator.Halfwave ectifier cemvents an ac veltoge in to a polsating de Voltage using only ome batt of the applied ac Ve tkoge - othe rectifying diode Conducts doning ove half of the ac gue only Figta) ond figlb) shows the basic cinevit and wave fonms of a half Wave nectifien| Openation ! lee vi be the _ to the Gea) of the tnansfonmen and given by the — eqpation Viz Vm Sint; Vin >> Vy whene Vz ts the cvt“im veltoge of the diede, > dering tre positive half cycle of the imput the encode ef the diede becomes mone pesitive with mespect to the Cathede and hence diode D conducts CFenwand 6 Fon an ideat diode the fomuand %* veurage drop ss Zeno+ $0 the whole impot Voltage — witt appean acnoss the lead mesistance (RL) + 2 Doing negative half cycle of the Inpot Signal, the ancde of the dicde becomes negative with nespect] ‘to the = cathode ond hence diode DP doesn't Conduct. Crevense bias) For an ideal diode , the impedance offered by the diode is infinity Hence the diode cendugts ho Comment | Hence the Voltage drop across Ris 7e70+ grat |compoments of Q Half Wave Recti | Hammonic the input input of the v; The Plax men on y Avene z Sinvseidal voltage tnonsfonmen is Vin Sinwe diode current er Load iG) =[ Day Sinwe where cunnent Con) De oe fed at the | of appl ven by — © Cumnent is Biven by) fer 0 wh ab Re » - ’ ——————— . Vams - ae Vale. z Vde T= (ey _, ; ey Go 3) Transfonmen vtilisati facton i- Ta the design of any Power supply , the nating | of the tnansfenmen sheuld be detenmined. This Can | i be deme with a Knowledge of the de powen delivered | to the load and the type of Mectifying cincvit used |