Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

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Presentation of Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Transcript of Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

  • 1. SUB : ELECTRONICS DEVICES & CIRCUITS (2131006)Topics :The Unbiased Diode, Forward Bias, Reverse Bias, Breakdown, Energy Levels, The energyHill, The Barrier Potential and Temperature , Reverse-Biased DiodeCreated by:Meghwal Dinesh S. 130140111041Mistry Keyur R. 130140111043Nakrani Pratik R. 130140111046

2. The Unbiased DiodeWhat is Diode :- A semiconductor device with twoterminals, typically allowing the flow ofcurrent in one direction only.What is Unbiased Diode :- when we do not apply anysource of energy or electricity than adiode is said to be unbiased diode. 3. The Unbiased Diode FORMATION OF P-N JUNCTIONp typesemiconductorn typesemiconductorAnodeCathodeJunctionP side is called as N type is called asHolesElectronesMajorityMinorityMinorityMajorityDiffusion is same 4. Forward bias If p region is connected to the positive terminal of external dc source & n region isconnected to negative terminal of dc source is said to be forward biasing.If IfForward biasing of a diode Symbolic Representation 5. Operation of a Forward biased Diode-----+++++++--The holes Converting intothe negative ions intoneutral atomesp nRCurrentlimitingresisterVDue to negative terminal of externalsouce connected to n-region soelectrons are pushed towards p-sideDue to Positive terminal of external souceconnected to p-region so holes arepushed towards n-sideThe Electrones Convertinginto the Positive ions intoneutral atomes Due to this Thewidth of deplationregion will reduceDue to reduction inthe depletion regionwidth the barrier alsoreduced.Hence a large numberof electrons & holes cancross the junction underthe influence ofexternally connectedDC voltageAs we can say that the flow of electrons is current so that the current producein this position said to be forward Current 6. Reverse bias If p region is connected to the negative terminal of external dc source & n region isconnected to Positive terminal of dc source is said to be reverse biasing.Ir IrReverse biasing of a diode Symbolic Representation 7. Operation of a Reverse biased Diode-----+++++The process of widening is not take place at longer time due tothere is no steady flow of current from n-side to p-side++--p nR CurrentlimitingresisterHoles in P region are attracted Vtowards negative terminal ofsupplyElectrones in n region areattracted towards positiveterminal of supply.Due to this The widthof deplation region willincresasesDue to increasesin the depletion regionwidth the barrier alsoincreases.Minority carrier in p-regionattractedtowards positive ofsupply.-----+++++So that few electrons are flow so the current is also tiny that current states at this positionsaid to be reverse saturation current due to minority carrier 8. BreakdownThe reverse saturation current flowing in reverse biased diode isdependent only on temperature &independent on reverse applied voltage externally.The breakdown in reverse biased diode can take place due to following effects.AvalacheeffectZenereffectBREAKDOWN 9. Breakdown due to Avalache effectDue to large voltagevelocity of minoritycarriers will increaseto great exentTherefore Kineticenergy also incresesWhile travelingminority carriers willcollide with stableatomes & importsome of kineticenergy To thevalance electronspresent in co-valentbandDue to thisadditional energythese electones willbreak the covalentbonds &jump intothe conductionband to free forconduction.Now this freeelectones will beaccelerated &theyknockout somemore valanceelectrons by meanscollisions.THIS CHAINREACTION ISCALLED asAVALANCHEEFFECT 10. Break down due to Zener effectDue to heavy doping ofp & n side of the diodethe deplation region isnarrow in reverse biasedcondition.Therefore electrical fieldwhich is the voltage perunit distance is veryintense across thedeplation regionThis intense electric fieldcan pull some ofvalence electrons bybreaking the covalentbonds these electronsthan become freeelectrons.The large number ofsuch electrons canconstitute throughdiode this is called asthe breakdown due tozener effect 11. Energy Levals Each electrons orbit has an energy leval associated with it. The electrons in the inner orbits aremore closely bound to the nucleus to the nucleus and posses less energy. As we move towards the valance shell, the bliding force between nucleus & electrons reducesand the electrons reduces & elctrones posses higher energy.Shell 1Lowest energyEnergy leval increses as we moveaway from the nucleusValance orbit hashighest energy leval 12. Energy BandsFirst bandFormed by clusterof energy leval infirst shellValencebandCorresponds tovalance electronspresent in differentatomes ofmaterialsEnrgy associated issecond highest.ConductionbandThe electrons inconduction bandare the freeelectrons.Enrgy associated ishighest.Concept of forbidden gap: Forbidden gap is energy gap that separates the conduction band & Valence bands. For any material the forbidden gap may be large, small , or even nonexistent. The materialsare classified as conductor , insulator, semiconductors based on relative widths of forbiddengap. 13. Energy HillEnergyConduction bandValence bandThe Valence &Conduction bandsare slightly lowerenergy levalsThis is Due to differencein the atomiccharacteristics of thepentavalent(n-type) &Trivalent(p-tpye) impurityatomesMinoritycarriers(electrons)Majoritycarriers(Holes)Majoritycarriers(electrons)Minoritycarriers(Holes)A p-region n-region K 14. Barrier Potential & Temperature Inernal temperature of p-n junction is known as the junction temperature Whereas the air surrounding the device is called as ambient tempreratureFor conductingDiodeJunction Temp. > Ambient Temp.Barrier Potential 1junction temperatureSo that Due to Incresed Temp. barrier potential decreases more electrons & holepair produced . These will diffuse into deplation region to narrow it down.The barrier potential of a silicon diode decreases at 2 mV per degree Celsius rise injunction temperature.-2mV/ = 15. Circuit Courtesy : Circuit MakerPlatformed by :- Microsoft office 2013