去年材料物理答案整理.docx

去年材料物理答案整理.docx

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去年材料物理答案整理

1.whatisthewave–particledualitytheory?

Doesanymatterhavebothwaveand

particlecharacteristics?

（33号）

1）Particle-likeCharacter:

lightpropagatingthroughfreespaceconsistingofastreamof‘photons’suggestedbyphotoelectriceffect.Itskineticenergyisgiven:

Wave-likeCharacter:

itscorrectnessisindicatedbyelectronmicroscopeaswellasbydiffractionandinterference.TheDeBrogliewavelengthofaparticlemovingwithmomentummvisgivenby:

2）anymatterhavebothwaveandparticlecharacteristics

2.Whatistheuncertaintyprinciple?

（Foranexample）（33号）

Uncertaintyprinciplestatesthatcertainpairsofphysicalproperties,likepositionandmomentum,cannotbothbeknowntoarbitraryprecision.Thatis,themorepreciselyonepropertyisknown,thelesspreciselytheothercanbeknown.

3.Wavefunctionanditsmeaning.（33号）

Awavefunctionorwavefunctionisamathematicaltoolusedinquantummechanicstodescribethemomentarystatesofsubatomicparticles.

Statisticalexplanationofwavefunction

Thevaluesofthewavefunctionareprobabilityamplitudes—complexnumbers—thesquaresoftheabsolutevaluesofwhichgivetheprobabilitydistributionthatthesystemwillbeinanyofthepossiblestates.

4.ThesolutionofSchrodingerequationoftheparticlesboundinone-dimensional

potentialwells.（1/2号）

Singleparticleinonedimensions：

Freeparticle

Timedependent

5,Whatisthebestobviouscharacteristicsofcrystallattice?

（3/4号）

Thebestobviouscharacteristicsofcrystallatticeisthatatomsarearrangedperiodicallyincrystallattice.

Acrystalorcrystallinesolidisasolidmaterial,whoseconstituentatoms,molecules,orionsarearrangedinanorderlyrepeatingpatternextendinginallthreespatialdimensions.

6.whatistheforbiddenband,emptyband,valenceband,conductionband?

（5/6号）

●allowedband:

theenergybandwhichallowtobeoccupiedbyelectron

●forbiddenband:

theregionbetweenallowband,inwhichelectronisnotallowedtooccupy

●emptyband:

theenergybandinwhichelectroncannotbefoundineachlevel

●valenceband:

theenergybandcorrespondingtovalenceelectron

●conductionband:

aboveValencebandtheallowbandwhichhavethelowestenergy

7.Usethetheoryofenergybandtoexplainwhatistheinsulator,semiconductorandconductor.（7/8号）

Solution：

Asisshownintheabovepicture,inmetalthehighestenergybandfilledbyelectronsisnotfull，furthermore，thedensityofelectronintheenergybandisveryhigh,ithasthesamemagnitudeasthedensityoftheatom,sotheconductivityofmetalisveryhigh.

Inthecaseofinsulator,thereisanenergygap,afiniteexcitationenergyisrequiredtocarrytheelectronsupoverthegapintothenextband.Thiscan’tbesuppliedbysmallconstantelectricfield,thentheconductivityisverylow，almostzero.

Asforsemiconductor,theenergygapissmall.AtthetemperatureTtherewillbeasmall,butnotzero,densityofelectronsexcitedbythermalfluctuationsintotheupperband.Theseelectronscaneasilycarryacurrent,whichwouldincreaserapidlyathighertemperature.

8,Whatisthemobilityofsemiconductor?

Whatarethefactorswhichhaveeffectonthemobility?

（第4个ppt,33-36页）（9/10号）

Answer:

Itistheaveragedriftvelocityofcarrierinunitelectricfield.

assumethesemiconductorisn-typesemiconductor,electronconcentrationisn0,theaveragedriftvelocityofelectronsisvd.

weknowthecurrentdensity（J）is:

Accordingtotheohm’slaw,

Wecanget

itistheelectronmobility

Similarily

istheholemobility

Sointheactualsemiconductor,

Butinn-typesemiconductor,n0>>p0

Inp-typesemiconductor,p0>>n0

Inintrinsicsemiconductor,n0=p0

载流子迁移率的影响因素很多，关于这方面比较系统的信息没有找到，但老师强调了一点，随着半导体中掺杂浓度的升高，其载流子的迁移率降低。

9,P-semiconductorandN-semiconductor.Theenergybandsketchofap-njunction.（11/12号）

N-semiconductor:

Theadditionofpentavalentimpurities,suchasantimony,arsenicorphosphorouscontributesfreeelectrons,greatlyincreasingtheconductivityoftheintrinsicsemiconductor.Inn-typematerialthereareelectronenergylevelsnearthetopofthebandgapsothattheycanbeeasilyexcitedintotheconductionband.

P-semiconductor:

Theadditionoftrivalentimpurities,suchasboron,aluminumorgalliumtoanintrinsicsemiconductorcreatesdeficienciesofvalenceelectrons,called“holes”.Inp-typematerial,extraholesinthebandgapallowexcitationofvalencebandelectrons,leavingmobileholesinthevalenceband.

Theenergybandofap-njunction:

Theopencirclesontheleftsideofthejunctionaboverepresent"holes"ordeficienciesofelectronsinthelatticewhichcanactlikepositivechargecarriers.

Thesolidcirclesontherightofthejunctionrepresenttheavailableelectronsfromthen-typedopant.

Nearthejunction,electronsdiffuseacrosstocombinewithholes,creatinga"depletionregion".

TheenergylevelsketchaboverightisawaytovisualizetheequilibriumconditionoftheP-Njunction.

10,Whatisthedirectbandgapsemiconductor?

Whatistheindirectbandgapsemi-conductor?

（13/14号）

Insemiconductorphysics,thebandgapofasemiconductorisalwaysoneoftwotypes,adirectbandgaporanindirectbandgap.Theminimal-energystateintheconductionband,andthemaximal-energystateinthevalenceband,areeachcharacterizedbyacertaink-vectorintheBrillouinzone.Ifthek-vectorsarethesame,itiscalleda"directgap".Iftheyaredifferent,itiscalledan"indirectgap".

11.Whatarefunctionsofthediodesanddynatrons（15/16号）

Themostobviousnatureofthediodesisitsone-wayelectricalconductivity.Theycanbeusedforrectification,clamp,detectionandregulation。

Theyhavetwotypesofspotcontactandfacecontact。

RectifierDiode:

Thediodeisone-wayelectricalconductivity,canchangethedirectionofACtransformintoasingleDCpulse.Switchingelements:

diodesunderforwardvoltageresistanceinsmallin-state,isequivalenttoaconnectedswitch;intheroleofreversevoltage,theresistanceoflarge,isoff,

DynatronshavearoleonAmplificationandswitching.Theycanbeusedforsignalamplification,oscillation,on-offcontrol.TheyhavetwotypesofPNPandNPNtransistor。

12.Showthetypesoffieldeffecttransistors（FET）andtheirfunctions;Pleasegivethebasicstructureandfunctionofthinfilmtransistor（TFT）.（17/18号）

答：

（1）TwokindsofFET:

●JunctionFET（JFET）

●Melt-oxidesemiconductorFET（MOSFET）

ThefunctionsofFET:

●Amplify

●Electronicswitch

●Variableresistor

（2）TFT

2）FunctionsofTFT:

ItcanbeusedasSemiconductorswitchesinLCD.Eachliquidcrystalpixelisdrivedbyintegratedthin-filmtransistors,whichcanbehighspeed,highbrightness,highcontrastdisplayscreeninformation

13．Whatarethebasicconditionsofamaterialwhichcanproducevisiblelightemission?

（19/20号）

Solution:

1、Theenergywidthofthebandgapislocatedatvisiblezone.

2、Theexcitons（electronandholepairs）havebondenergy.

3、Theexcitonshaveenoughlifetime.

14．whatisthePhotoluminescence（PL）andwhatistheElectroluminescence（EL）.（21/22号）

（电致发光（electroluminescent）是通过加在两电极的电压产生电场，被电场激发的电子碰击发光中心，而引致电子解级的跃进、变化、复合导致发光的一种物理现象。

光致发光物体依赖外界光源，从而获得能量，产生激发导至发光的现象。

）

Photoluminescence（PL）：

theobjectirradiateddependsonexternallightsource，togainenergy，produceexcitation，leadtothephenomenonoflight。

Electroluminescence（EL）：

Byaddingtwovoltageelectrodescreatesanelectricfield,theelectronicexcitedbyelectricfieldcrashingluminescencecenter,resultingine-solution-levelleap,change,compositeleadinglightofaphysicalphenomenon。

Electroluminescence（EL）

Photoluminescence（PL）

15.Measurementoflight-emittingdiode（LED）.（23/24号）

Solution:

theluminousefficiencyistheratiooftheluminousfluxemittedbythedeviceandtheconsumedelectricpower.

16：

Howmanytypesofphotovoltaicsolarcellsdoyouknow?

（25/26号）

Answer:

1.Crystallinesilicon（Si）solarcell,whichincludessinglecrystalSisolarcellandpolycrystallineSisolarcell;

2.Thinfilmsolarcell,whichincludesSisubstratethinfilmsolarcell,Cu/In/Ga/Se（CIGS）thinfilmsolarcell,organicthinfilmsolarcell;

3.Multiplecompoundssolarcell,whichincludesCdTe/CdSsolarcell,Ⅲ-Ⅴgroupcompoundsolarcell;

4.Dye-sensitizedcell;

5.Organicsolarcell;

6.Nano-crystalsolarcell;e.g.nanoTiO2crystalchemicalenergysolarcell.（FromBaiduwebsite）

17.Current-Voltagecurveofphotodiodes.Whatarethedifferencesofthephotovoltaiccellsandphoto-detectors?

（27/28号）

Itisthecurrent-voltagecharacteristicofaphotodiode.Whenthephotodiodeisforwardbiased,thereisanexponentialincreaseinthecurrent.Whenareversebiasisapplied,asmallreversesaturationcurrentappears.

Photovoltaiccellsarearraysofcellscontainingasolarphotovoltaicmaterialthatconvertssolarradiationintodirectcurrentelectricity.Operatingdiodeinfourthquadrantgeneratespower.

Photo-detectorDiodecantransformopticalinformationintoelectricalinformation.Itisoperatedinthethirdquadrant.Inprinciple,allphotovoltaicdevicesarealsophoto-detectordevices.ThemostimportantFactorsdifferentfromphotovoltaicdevices:

1、theratioofthecurrentunderphotoilluminatedtodarkstate

Iphoto/Idark;

2、theresponsevelocityofthedevice.

3、theresponseispartiallylocatedinfraredzone

18．theenergyefficiency,Voc,IscandF.Fofphotovoltaiccells.（29/30号）

Energyefficiency:

Voc:

开路电压，opencircuitvoltage

Isc:

短路电流。

Shortcircuitcurrent

FF填充因子

19,Measurementofsolarcells.（31/32号）

I-VCurveofsolarCellMeasureDiagram

Figure1Figure2