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lat wy LOMbiLe bo i co wh Gus eve b Bands in solids 7 Lahn periodic field provide: ., 6 oy SI 6 sm! : : D theory for ee oll 4. Insolid atoms occupies the lattice ce lat ry OF order 88 that of the linear dimension : an, tt « internal electric field, which ;..* wee age in solid interest S' i es hich ig cing Therefore, atoms ? itd pau 4 fours? ry bond : wou. eg [shh est ‘ firs “4 oll sand engineering feet with the theory and use of the branch of S — gas or semicon ducts lag, Ir. aa hich efectrons are fransported thr ; =e in which ef : ne is usually controlled by elect: oF Felecirons in such a device called electron deviet © usually {rolled by sent Te 5 ors etc. are exalml Je of electronic levice. cl Diode, tt 4.1. Energy velO} Jix de “oe 7 ular called band nik : n the atom is 0 . pect uD : eA Aas Formation of Energy Band in Solids: ngs t The solid crystals are formed when the isolated atoms are brought together. Various intera, mater! rticular interatomic spacing d, there is a “ie 4 TOper Af the s ze occur between the neighboring atoms. At a pa ‘ |. In this process, the changes occur in i Ie wth : balance between forces of attraction to form a crysta ofa single atom, there is a single energy fo T an pur? nrt~4 electron energy level configurations. In case two atoms are brought close to each other, it leads to intermiy; ixing Hi electron orbit. However, when of electrons in the valence shell. As a result, the number of permissible energy levels is f ‘ormed, | Ty which is called an energy band. Vv * 7 Three bands are important from the conductivity point of view, which are LValence band 7 ype 27 3, bauds Fi pe tig band bf Types -Forbidden gap or band wo a y j we) | The simple energy band diagram, showi ergy band diagram, showing these bands is shown in the figure ges 4 1 ewer} vation Bor! pat wr yt Ge comply gach? ) = ee a thin A an, ce oh — sre ow Pilied | 4 . by tole 1" beng Canny | pavd) i. itleads St Lins NEY kei re, In the no valence band and the conduction band is empty. Hence the electrons! d valence shell. are called valence electrons and the outermost shell is calle t highe! n At high d move to the conduction band as js not allowed to oc: etemlecttOns. ed to occupy any energy state in forbidden gap. These electrons are called SD px eremel nove 9.4, oY) vig Sd iven type of materi F Oath anual the forbidden energy gap may be large, small oF tonseristent. © = erials as insulators, conductors and semiconduc! t on the widths of the forbidden energy gap tors is mainly y 3 pr mere”? temperature, these electrons acquire energy an « For any e clas’ dependen' pes of Materials (Insulator, Semi-conductors. Conductors) meet y ding to the classical free electron theory, electrical conduction can occur in a solid if lectricity materials are Accor = e electrons are available. Depending upon the ability to conduct ¢! classified into three types. Ge ah vw > allow f fo Flow cnen oma ours\oAP 1.Conductor 7,Semiconductor Ly vabmus eonlu 3 Insulator z& 2 Otv e of the most useful classification schemes for electrical properties involves grouping Wh \\al 7 cova” d upon the following two criteria: A at ral dat 0K, itis a conductor. materials base i Jf the solid is characterized by a partially filled valence ban 7 If the valence band is completely filled at ok, the solid is either a semiconductor oF insulator = 2 Ae ly Jury palle 7 Ge on COM? agen The distinction between a semiconductor and an insulator is based on the magnitude of the energy gaP- wv wv ov ave Q\t “tect ale ° (1) Conductor we Conductors are characterized by high electrical conductivity. These are the solids in which plenty of free electron are available for electrical conduction ¢.8- silver, copper and aluminium. In general, electrical resistivity of conductor is very low and is of the order of 10° Qem. In this there is no forbidden gap and the conduction band and valence band are overlapping each other. across the conductor causes 4 free electron to constitute electric So, a slight potential difference current. ob > Valence Band Band Energy Energy bands in Conductors
‘i ¢ ié ductor 4 “8s (a) Intrinsic Semiconductor GBM 7 pure se qouess "8 ee y 10 Oy intrinsic semiconduct js The intrinsic sei Ors are pure s i i —~ laevis The elemental and conn miuctor materials. These semiconductors possess S “ poor Up peer. conae pound a aay can be intrinsic type. a oft € a The in semiconductor is ye aa Kt Fehectrore ? TL oalece bend can ry nae very small. So even at room temperature some of electrons \ eC from . Son be pee conduction band by acquiring thermal energy. The jump Y) CS db hoje in the valence band. The process is galled as the generation of an electron hole pair. In pure _ <4) semiconductor the number of electrons in the conduction band and holes in valence bands are equal. : Jomperseages how a OT aor from band eorbend czcaies holes poe .vde n ty When the electron jumps in to the conduction band, the atom acquires a positive charge equal are > ey to the charge of. electrons. The absence ofan electron in an atom is called a hole. When a voltage aD ig 1 a applied toa “airs the electron in the conduction band accelerates towards the positive PS terminal and holes in the valence band move towards the negative terminals. Hence the current cemperain, . conduction takes place due to the movement of both the charge carriers’ electrons and holes. ' forbidden x, a Gren cemiCon auctor Gute rte * 1 . (2) Extrinsic Semiconductors a Extrinsic semiconductor is an impure semiconductor formed from an intrinsic semiconductor P by adding a small quantity of impurity atoms also called dopants. The process of adding No ve fo impurities to the semiconductor ci i ine-This added impurity is very small of the order of one atom per million atoms of pure Semiconductor. Depending upon the type of youn impurity added the extrinsic semiconductors are classified as: \S cweated b qaly p- Type Semiconductor Ss My ea ige or Zddin 9 GS ugk n- Type Semiconductor Biersoved Gm ou nt 21 Forpuasty +o (1) p-Type Semiconductors Var Tear oun ae SWF The extrinsic p-type semiconductor is formed when a trivalent impurity is added to a pure are created in i semiconductor in a small amount, and as a result, a large number Of ho z latgeniimber of holes are provided in the semiconductor material by the addition of trivalent Impurities “Tj and indium. Such types of impurities which produce p-type Wt et gallium_and 2 f SeniconaeIET are known as an acceptor impurity because each atom of them create one hole if Can accept one electron. A trivalent impurity like gallium, having three valence electrons gemianrn eotmanium crystal ina small amount. Each atom of the impurity fits in the { ‘Mm crystal in such a way that its three valence electrons form covalent bonds with the - Mzounding germanium atoms as shown in the figure, <=> fexor, Grellcer, L, gaint Page 38 of 75 alt a5 waatum THM Semiconductor Physic, 7 ia contributes a manium atom hol ete fi h covalent te -the fourt eal sae spree as a Hole. Boe ote secon shor. Ti nical HES emely small amo the semico lectron short. This mis: ol AS an ext nly sal ame hole in the mye bole mnillio therefore, it pro’ number of atoms, nt bonds, In the fourth covalent y in by the mber of holes are created by a large nu ied across this type o1 S i ctor as : this t f semiconduct lied 4 potential difference is a) ee Holes i add tas | "" ‘ ©) 0 , (" ) mn 4x 05°" fi ws She? “1 NTE ayo no ® yo” opt? ] Electron The electrons Movable than holes holes is Poor as the hole pairs are for little amount of ee FOP, Cyt < o q, ae oh = . soy i r) ig PAE Saco ducroz= Mat Bad ay gemicov ductor material types, jon we iconduc 4.4, P-N Juncti ae silt Oo SI a boundary between a8 or : qe bias A p-n junction is an pore asemiconductol. = 4y olen Dahm . J 1 e, e + a , the p-type and the n-typ' E yunction is Pocs: if gt =. 4r- tral preuion ort New : x Yo” Neutral n-region ep ~ The 5 Np (Donor) > i ¢* PhO ee MT Oe ae ao f) Fhe -side or the positive side of the semiconductor has an excess of 10 CS an : ie 0 v’ sot cating side has an excess of electrons. In a semiconductor, the p-n junction is created by o* i 4 method of doping. — p on Junction [> Crcott (Formation of P-N Junction) by ocepin eewe know, if we use diffetent semiconductor materials to make 4 p-n junction, there will 72 a grain boundary that would inhibit the movement of electrons from one side to the other Scattering the electrons and holes and thus, we use the pr ping. We will underst the process of doping with the help hin p-type sili Semniconductor sheet. If we add a sm f the 10S Fyom p-sihe dito 7 coos Fegion of positive charge pletion region. Due to this 9 that of the diffusion current the 2 S104 d negative charge on positive space charge Que to res q@edia vit, poo Oitgubion process IN7, Uhictsons From wn-sics ditt 88 Of holes And thes, he PU Junction ise But before we can use the PN junctio i ice or as a rectifying device we need to that is connect a voltage potential across it. On the voltage axis above, firstly bias the junction, “Reverse Bias” refers to an ex v J enepidn i 0 Cathode (K) Anode (A) AewoSS fre “TCA Forward Deu dion " + Current inte 00 0 - sick. ——— Conventional Current Flow rowed as Reverse - = Breakdown peee Voltage = NV —< = - Reverse Voltage Forward Voltage \ Leakage Current s “Zener” <20uA Silicon peal Breakdown <50uA Germanium EN Src or Avalanche Region aoeing — we ie jas x 5 Reverse bias Ths s (™A)Y Current ee ternal voltage potential which increases the potential barrier. An ye extemal voliage which decreases the potential barrier is said to act in the “Forward Bias’ ppin d rake % p-n uct girection. as from er There are two operating regions and three possible “biasing” conditions for the ng. sachin di : HE s.of dopns bo standard junction diode and these are: Bs NO voltK~y is applied fo PP sider # " ee : ee ee ss “iy i) itis’ # Zero Bias - No external voltage potential is applied to the PN junction diode. eet in * Reverse Bias — The voltage potential is connected negative, (-ve) to the P-type material and @ diode which has the effect of increasing the pee, (+ve) to the N-type material across Junction diode’s width, “> Tope 7 ~Vve which incercedA : *Forvard Bi aes CNL dene Leith 4 potent ward Bias — The voltage potential is connected positive, (+ve) to the P-type material and vam tegative, (ve) to the N-type material across the diode which has the effect of decreasing the PN junction diodes width ee PTI OD YO ys v re >-ve OO eae ‘be Page 42 of 75 Ry! NX | : J 5 | + + Iwider depletion! eee | o— pp om Be Reverse Biasing Voltage This condition represents a high resistance value to the PN junction and practically zero current _ flows through the junction diode with an increase in bias voltage. However, a very small reverse jeakage current does flow through the junction which can normally be méasured in micto- gs does How through the can norm iu amperes. a ne final point, if the reverse bias voltage Vr applied to the diode is increased to a sufficiently high enough value, it will cause the diode’s PN junction to overheat and fail due to the avalanche effect around the junction. This may cause th diode to become shorted and will result in the flow of meximunr circuit current, and this shown as a step'd lownward slope in the reverse static characteristics curve below. L> 1b wevev& bias voliap~ © Ines casas, it will Cree ; ‘ a) Reyerse Characteristics Curve for a Junction Diode Aiadtis pv Je4 eal % Jp Ovesregk 4 fei) Ve} Reverse Voltage, (-VR) : 0 1 1 1 10nA 100nA mA Reverse Current, (a) pt from The condition represents nts to flow through th lode Serre across the junction or pee acts 0.3v for germanin, app’ the low Te: With on] diode is k m and @PProximate: the diode can conduct “infinite” curre: ince ircuit, therefore resistors are use, ihe its maximum forward cu; eni oer ine of heat than it was designed jn the ” allowing very large oltage. The actual potential n of the depletion layer at ‘On junction diodes, S€ in bias y, ant by the actio ly 0.7y for silic, nt above this knee Point Snes with the diode P&Cification causes the devi 1 for resulting in » very quick as it effectively becomes a to limit its current flow. Ce to dissipate more power failure of the device, RG 48 OC cedediar SY a pN Junction Diode as a Rectifier _ hy ‘ lication of p-n junction diode j, i circuits. These Circuits are used to ~ \ The Ore conversion of A.C signals to Power supplies. Diode rectifier gives an vk en itage which Pulsates in accordance with time. The filter smoothes the pulsation in 4 jrernating V' d to produce D.C Voltage, a Tegulator is used Which removes the ‘ripples. There Pa e voltage = methods of diode rectificati oo Py mary Ne rectification: 3 Ngee Vert gos ty i¢ Wave Rectifier ot en Pare weve ye “0% } lage ve Rectifier ie yer vot ‘ GS SP AS 2} e Ri iS ¥ed g S$ te , Full Wav aw os = yecd§ Lito HE Aes G8 oy mo ‘ ¢ / ‘ etifier 7 i Mesias! i the p-n junction diode? palf Wave Re ifier, one half of each a.c input Cycle is rectified. When the p-nj ic JBo he ne liftle resistance and when it i In hale it gi ee y death y reversing biased it provides ce EB is forwar -half cycles, the diode is forward biased when the input voltage is applie Y on" Se Daring one cycle, it is reverse biased. During alt —— the opposii and in ine mate half-cycles, the optimum > t euch > ge stat Hoos ined. & ey resi can be obiaines {besa to bis forests) doxward « Oo Rectifier ing of Half Wave Working 0 L x 5 itive half of the both positive and negative tach wil gee ee ea ot ete half-wave es Eo paitive fo negative which will generate only a po: \ Ne ill flow lo input, the current w) Hoy i i sformer, the voltage will be ly is applied to the transf x ul tee | fe of the ac supply: Meine Chine diode. All the variations in the a.c supply will r ne i Ge F econdary Wi ‘ltée egreasing at the s : ‘ Ovyp+ ting D.C voltage to the load resistor. Cy 0e 1S rng cotpy OVP h ‘ Ta and we will get t Cre ; D1 : a) Te current waveform Wt og = fier = Cavemen ore) Php Cball ans : i. ill be 3 itive and the diode will Inthe second half cycle, the current will flow from negative to positive Teerse biased, et and we cannot 8 NS, at the output side, there will be no current ee g reverse bias iret at the Tesistance. A small amount of reverse current will flo iers, Page 46 of 75 (or A + nductor Physics a oentifior “avantages of Half Wave Rectific pe Affordable ‘> it ions + Simple connectio sate ynnections « Easy to use as the co’ ‘dare less Number of components use ‘ ier Disadvantages of Half Wave Recti Ripple production is se Harmonics are generate 4 « Utilization of the transformer Is ve ear e « The efficiency of rectification 1s lor Rectifier with a transformer for py Applications of Half Wave ‘ Tainan: Following are the uses of half-wave Reece i gaed alone i rec Power rectification: ‘Half wave Pein rectification as powering equipment. | modulating th aM sional Signal demodulation: Half wave rectii i 5 a * Signal peak detector: Half wave rectifi bea sre WG\VeS oF gr pairve a OOF mee oa ee SMa alee! ae current whig . tage or outpu' Full-wave rectifier circuits are used for producing Se alt wave rectifier is that sud purely DC. TI ain advantage of a full-wave rectiier ~ ipple- produce fee iGces iit Salat is fg Rec WET rectifier, there is less ripp e pl in wave rectifier when compared to the half-wave rectifier. avert Pu negate pulses Working of Full Wave Rectifier 7 ‘ ' function ie The full-wave rectifier utilizes both halves of each a.c input. When the p-n junct ‘Or ig biased it gives high re: biased, the diode offers low resistance and when it is reversin, Q 4 The circuit is designed in such a manner that in the first half cycle if the diod 1 bid itis reverse biased and so.on:—¢-5—¢ So" cGyection then in the second half cycle The input AC supplied to the full wave rectifier is very high. ifi wre simple are used for der eek used for detecting the peal waveform. During the positive half cycle, diode D1 diode D2 is reverse biased as it f Secondary winding while secondary winding. Due to this, diode D1 will Conduct actin, acting as as conduct acting as an open circuit During the negative half cycle, the di i Z cea rail cycle, lode D1 is re i : F biased because the top half of the secondary cron oe oh ices D2 the circuit becomes positive, Thus, ina II wave rectif Bee ae u postive and negative balfcycle ADE solage 5 x 7 i” pes elels 2 Pl > foswesed bi. P25 Reve. bial Of wil Oct ab & Oo LJ Polytechnic BARN Mik> D> he heey to | Pp 68 — —<—$<—— psence of the expensive centes SS ——— tio’ = eaeat DO). The main advantage of this cont ‘are reduced. 5 HES - i fey tapped transformer. Therefore, the size and cost 0 repped Tose, j Pree neaslores A pc Output ignal is obtai The input signal is applied across terminals A and B and eres are arrange: ae the load resistor RL connected between terminals C and D. aE : oe aS In suc} a way that only two diodes conduct electricity during each alt oe a; L46% a fy esistance & ‘etsy. When Working of Photocell nla € working principle of a photocell can depend on the occurrence of is Connected the effect of photoclee photoelectric. This can be used to change light energy into electrical eni ¢ emitter terminal is connected to the negative (-ve) terminal & collector terminal to the positive (ve) terminal of a battery. Geainex > -we, Colle ctay s euP radiation will be more than the material’s threshold freque! The frequency then photo issi i 3 n current will be there’within the circuit. If the radiation intensity fe enhanced, then the hotoelectric current will be i crease, rr Eee: P ane wh If xedeation &M FeRs} he ir) Ler Applications of Photocell S Enhened, p The applications of Photocells include the following. Beret Engineering Physics > Photo voltae ct tec —A— eo —— Solar cells or photovot ight into dire ee made 4 taic celts convert sunlight into qi; are base: » PI rect Curr, based on the principl ‘ i ‘photovoltaic effect," which sencen (OC) electricity Ligh eee phatowalinis effect. They S electricity crystals induces lea Tighs reecheaant > when bint nits, photert yeroh So vtim When light reaches the p-n junction the | Sup lIES B76 rey 4 fe ©” Pore, cverfmy very thin p-type layer. The light enones '2ht Photons can easily ent ‘ the junctich-te-ereate a num “ph ane Rew ae N- Fepet p-regpe mcdenter Photon Absorbed 40% bewuc es poenpies firld ~ ae in Depletion Zone in bee” Pus lyjots attnps vi Photon Front Electrical Contact Feld pasted NType holes to p Fype <—Depletion Zone * TOW rype — fons las bof cies aS Lal 1. No pollution associated with it- How to balance Sor 2. It must last for a long time. ' ' 2 3, No maintenance cost. a VE en telat SW ty Careceti rs £ oe Disadvantages of Solar Cell s hig/h ca} 1 Ithas high cost of installation. atticie “4 2, Ithas low efficiency. aide 3, During cloudy day, the energy cannot be produced and also at night we will not get solar nergy, S Rainy wre, clo «Al, Show Uses of Solar Generation Systems U ee ims oferg ‘ “1 ay be used to charge batteries. <> @he-’ ses 6 G if ‘ee inlight meters. Lyte 4It my 0 power calculators and wrist watches. UL, Go fp,lakor) WF ny in be used in spacecraft to provide electrical energy. 
