北化大材料导论讲义第9章 比较与选择(共2学时)(彩色版)

Ohm’sLaw:欧姆定律Resistivity:电阻率V=IR(Ω-m)Conductivity:σ=1/ρ(Ω-m)-1电导率Conductors~107(Ω-m)-1Semiconductor10-6~104(Ω-m)-1Insulators10-10~10-20(Ω-m)-1防静电材料：10-5~10-9(Ω-m)-1Materials一些金属的室温电导率MetalElectricalMaterials一些金属的室温电导率MetalElectricalconductivities(Ω-m)-1Copper(铜)Aluminum(铝)Brass(70Cu-30Zn)Platinum(铂)Plaincarbonsteel(碳钢)Stainlesssteel(不锈钢)一些陶瓷的电导率一些陶瓷的电导率MaterialGraphite（石墨）Concrete(dry)（混凝土）Soda-Limeglass（钠玻璃）Porcelain（陶土）Borosilicateglass（硼玻璃）Aluminumoxide（氧化铝）Fusedsilica（熔硅）ElectricalConductivity<10-13<10-18一些聚合物的电导率Material一些聚合物的电导率MaterialElectricalConductivity[(Ω-m)-1]Phenol-formaldehyde（酚醛）10-9-10-10Polymethylmethacrylate（有机玻璃）<10-12Nylon6,6（尼龙）10-12-10-Polystyrene（聚苯乙烯）<10-14Polyethylene（聚乙烯）10-15-10-17Polytetraftuoroethylene（聚四氟乙烯）<10-17EnergyEnergyEnergy2sEnergyEnergyEnergy2sElectronstateIndividualallowedenergystates1sElectronstate12个原子的情况ElectronEnergyBand(电子能2sElectronenergyband(12states)1sElectronenergyband(12states)Interatomicseparation（原子间距）EnergybandEnergybandgapEnergyband原子间距平衡间距EmptyEmptybandBandgapEmptystatesFilledstatesEmptybandFilledband代表：一价金属（铜）代表：二价金属（镁）(a)(b)EEff(c)(d)Bandgap>2eVBandgap<2eVEmptyconductionbandBandgapFilledvalence bandEmptyconductionbandBandgapFilledvalence bandEmptyEnergyFilledEnergyConductionbandBandValencebandEmptyEnergyFilledEnergyConductionbandBandValencebandElectronexcitationffFreeElectronElectronexcitationHoleinvalence bandEgEScatteringeventsEScatteringevents（散射）电子迁移性电子净运动Driftvelocity:Vd=μeE迁移速率Electronmobility:μe(m2/V-s)电子迁移率Conductivity:σ=neμeMathiessen’Mathiessen’sLawt–thermal（热）i–impurity（杂质）d–deformation（形变）INFLUENCEOFTEMPERATUREρ0与a为材料常数INFLUENCEOFIMPURITIESINFLUENCEOFIMPURITIESimpurityconcentrationciintermsoftheatomfraction杂质浓度为原子分数Foratwo-phasealloyconsistingofαandβphasesINFI.UENCEOFPI.ASTICDEFORMATIONElectricalElectricalresistivity(Ω-m×10)Cu+3.32at%Ni54Cu+2.16at%NiDeformed43at%at%Ni2Cu+1.1221“Pure”copper“Pure”00+50–250–200–150–100–50Temperature(°C)0+50Intrinsic:电性能由电子结构所决定Extrinsic：电性能受杂质原子控制铜镍合金的室温电阻率与组成的关系Electricalresistivity(Electricalresistivity(10-8Ω-m)40200Composition(wt%Ni)INTRINSICCONDUCTIONINTRINSICCONDUCTION EField.........●..ooooFree:"Si:Si:electronOOHoleoooo材料带隙电导率电子迁移率空穴迁移率MaterialBandGapElectricalElectronHoleConductivity[(Ω-m)-1]MobilityElemental材料带隙电导率电子迁移率空穴迁移率MaterialBandGapElectricalElectronHoleConductivity[(Ω-m)-1]MobilityElemental0.050.672.20.380.182.25III-VCompounds0.002GaAs0.45InSb0.17II-VICompounds0.07CdS2.40-ZnTe2.260.030.01Mobility(m2/V-s)EXAMPLEPROBLEMEXAMPLEPROBLEM迁移率分别为0.14和0.048m2/V-s。SOLUTIONσ=neμe+peμhσ=ne(μe+μh)=pe(μe+μh)EXTRINSICSEMICONDUCTIONEXTRINSICSEMICONDUCTION所有工业化的半导体都是extrinsic;其电性质由杂质所决定。Extrinsic半导体(bothn-andp-type)都由高纯度单质制得，杂质浓度约10-7at%.制备过程中人为掺入预定量的电子供体或受体。这种掺混称为doping（掺杂）.n-TypeEXTRINSICSEMICONDUCTORn-TypeEXTRINSICSEMICONDUCTORPPEFieldConductionbandEnergyBandValenceband传导带中的自ConductionbandEnergyBandValenceband传导带中的自g供体态E’Eep-TypeEXTRINSICSEMICONDUCTORp-TypeEXTRINSICSEMICONDUCTOREFieldBBHoleEnergyConductionbandBandValencebandEgEnergyConductionbandBandValencebandEgpEXAMPLEPROBLEM2高纯硅中掺入磷使产生室温下浓度为1023m-3的(a)掺杂后的材料为n型还是p型?(b)假设材料中电子与空穴的迁移率分别为0.14和0.048m2/V-s，求其室温电导率。SOLUTION(a)SOLUTION(a)磷为VA族元素，在硅中为电子供体，故1023m-3浓度的载流子应全为电子，这一电子浓度远大于纯材料的(b)计算电导率时只考虑电子即可：e温度对电导率的影响10,000Temperature(oC)-200–100010040010000.0052at%0.0052at%Intrinsic0013at%Intrinsic5010020040060010001500Temperature(K)Electricalconductivity(Ω-m)1,0001001010.10.017001000–100–150–200温度对载流子浓度的影响lnn,p(m-3)60585654525048电子与空穴(Intrinsic)电子与空穴(Intrinsic)10101010101010载流子浓度(数目/m)00.0020.0040.0060.0080.0100.012温度(K)空穴(Extrinsic)0.0052空穴(Extrinsic)0.0052at%B空穴(Extrinsic)0.0013at%BgC为与温度无关的常数，Eg为带隙能，k为Boltzmann’s常数σ三neμp2kTlnplnpIntrinsicSaturationExtrinsicΔlnp=_E1/TEg=_2k=_2klnn=lnp≅C'_Eg2kTEXAMPLEPROBLEM3SOLUTION锗的Eg值为0.67eV,代入公式lnσ≅C_=ln(2.2)+=13.83纯硅室温电导率为4×10-4(Ω-m)-l。现欲得到一种室温电导率为150(Ω-m)-l的n型硅材料。确定一种杂质物并求其所需浓度（原子百分比）。假定电子与空穴的迁SOLUTION使硅成为SOLUTION使硅成为n型半导体的杂质元素在周期表中必然处于硅的右又因在n型材料中n»p,电导率只是自由电子浓度的函数。由杂质原子全部有效的条件，自由电子数就等于杂质原子数：n~Nd查表得到电子迁移率为(0.14m2/V-s)，代入所要求的σn=Nd=_19C)(0.14m2/V•s)21m_3=单位体积中的硅原子数单位体积中的硅原子数NSi为:NSi=28m_3NAρSiASi(6.023×1023atoms/mol)(2.33Mg/m3)28.09g/mol故杂质原子的百分比为：C'd=Nd×100Nd+NSi6.7×1021m_3(6.7×1021m_3)+(5×1028m__5xHallxHallEffectBz+z-VHdcIxyRH为材料常数，可用上式测定金属的电子传导：ee亦可测EXAMPLEPROBLEM4铝的电导率和电子迁移率分别为3.8×107(Ω-m)-1m2/V-s。在电流为25A，磁场为0.6tesla条件下求厚度为15SOLUTIONRIB首先应求出Hall系数RH再求出V再求出VHRIBVH=Hxzd_11V=_8V_3mp-siden-sideP型P型N型Battery结合区BatteryCurrent,IP-NCurrent,IP-N结的电流-电压关系+IForwardbiasBreakdown-–V0+I+VVoltage,VReversebias-Current,IVoltage,VCurrent,IReverseForwardReverseForwardReverseForwardP-N结的整流作用+V(a)–VTimeI0I(b)TimePNPPNP型三极管发射极基极收集极n-Typep-Typen-TypeNPN型三极管p-Typen-Typep-Type三极管的放大作用三极管的放大作用Forward-biasingvoltage正向偏压OutputvoltageReverse-biasingvoltage反向偏压Collectorn收集极LoadEmittern发射极Basep基极IEmitterIEmittern发射极Ie=Irb+IcIrb<<IcCollectorn收集极Load三极管的放大原理IBasep基极I=IeVe/BIp-Typechannelp-TypeSip-TypeSin-TypeSisubstrateMOSFET(metal-oxide-semiconductorfield-effecttransistor)SourceGateDrainSiO2insulatingResistResistResistGlassmask光降解隔层ResistExposedresistMetalMetalGlassmaskResist光固化隔层<二>Ion<二>Ionbeam,100keVAs+Implantedregion电荷密度（介电位移）D电荷密度（介电位移）D0=ε0ElVacuumE=V/lD=εE=ε0E+PVl介电常数V真空电容率PP=D_D0=(ε_ε0)E=ε0(εr_1)EQ0ADDDielectric0D0=ε0EQ0=D0A=ε0EAE=V/lD=εE=ε0E+PQ=DA=εEAP=D_D0=(ε_ε0)E=ε0(εr_1)EEXAMPLEPROBLEM一平板电容的面积为EXAMPLEPROBLEM一平板电容的面积为6.45×10-4m2，相距2×10-3m，板间电压为10V。两板间填充材料的介电常数为6.0。求：(b)平板的电荷量(c)介电位移D（电荷密度）(d)极化率PSOLUTIONε=εrε0=(6.0)(8.85=5.31×10_11F/mQ=CV=(1.71×10_11F)(10V)_10CVP=D_ε0E=D_ε0l=2.22×10_7C/m2V + +VacuumVacuum_+QAreaofplate,A–Ql表面上的净负电荷为-Q表面上的净负电荷为-Q’无净电荷区域表面上的净负电荷为+Q’=PA+-+-+-+_+-+-+-+_+-+-+-+_+-+-+-+_+-+-+-+_+-+-+-+_+-+-+-+_–Q–Q’Q+Q’+_VPNofield+AppliedEField++-++--++-++--++-++-+++--------+-+--++-+++-++--++-++--++-++-+++--------+-+--++-+++pipi=qdiP=P+P+P++++++----------E----E----------(a)(b)Orientation IonicElectronicDielectriccon