1、Chapter 4 Semiconductor devices4.1 Ideal pn junction4.2 pn Junction Band Diagram4.3 Bipolar Transistor4.4 Junction Field Effect Transistor4.5 Metal Oxide Semiconductor Field Effect Transistor4.6 Light Emitting Diodes4.7 Solar CellsFrom Principles of electronic Materials Devices, SO Kasap (McGraw-Hil
2、l, 2005)4.1 Ideal pn junction4.1 Ideal pn junction4.1 Ideal pn junction4.1 Ideal pn junction4.1 Ideal pn junction4.1 Ideal pn junctionME(x)(e)xEo-WpWn0VoV(x)x(f)PE(x)Electron PE(x)eVox(g)-eVoHole PE(x)Considering an abrupt pn junction:net(x) can simply be described by step functions shown in Fig. (d
3、). Using the step form of net(x) in Fig. (d) in the integration ofgives the electric field at M. ME(x)(e)xEo-WpWn0VoV(x)x(f)PE(x)Electron PE(x)eVox(g)-eVoHole PE(x)Integrate the expression for E(x) in Fig. (e) to evaluate the potential V(x) and thus find V0 by putting in x=Wn.W0=Wn+Wp, is the total
4、width of the depletion region under a zero applied voltage.ME(x)(e)xEo-WpWn0VoV(x)x(f)PE(x)Electron PE(x)eVox(g)-eVoHole PE(x)The simplest way to relate V0 to the doping parameters is to make use of the fact that in the system consisting of p- and n- type semiconductors joined together, in equilibri
5、um, Blotzmann statistics demands that the concentrations n1 and n2 of carriers at potential energies E1 and E2 are related byME(x)(e)xEo-WpWn0VoV(x)x(f)PE(x)Electron PE(x)eVox(g)-eVoHole PE(x)Considering electrons (q=-e), we see from Fig. (g) that E=0 on the p side far away from M where n=npo, and E
6、=-eVo on the n-side away from M where n=nno. ThusWhich mean that Vo depends on nno and npo and hence on Nd and Na. The corresponding equation for hole concentrations is clearlyME(x)(e)xEo-WpWn0VoV(x)x(f)PE(x)Electron PE(x)eVox(g)-eVoHole PE(x)RearrangingAndWe obtainWe can now write ppo and pno in te
7、rms of the dopant concentrations inasmuch as ppo=Na andForward bias: diffusion currentForward bias: diffusion currentForward bias: diffusion current(b)Forward bias: diffusion current(b)Forward bias: diffusion currentLaw of the junction is an important equation that we(b)Forward bias: diffusion curre
8、nt(b)Forward bias: diffusion current(b)Forward bias: diffusion current(b)Forward bias: diffusion current(b)Forward bias: diffusion currentxJn-regionSCLMinority carrier diffusioncurrentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority
9、carrier diffusioncurrentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority carrier diffusioncurrentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority carrier diffusioncur
10、rentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority carrier diffusioncurrentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority carrier diffusioncurrentMajority carrier
11、diffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecxJn-regionSCLMinority carrier diffusioncurrentMajority carrierdiffusion and driftcurrentTotal currentWn-Wpp-regionJ = Jelec+ JholeJholeJelecSchematic sketch of the I-V characteristics of Ge, Si and GaAs pn JunctionsGeSiGaA
12、sCurrentVoltage0.1 mA0 0.2 0.4 0.6 0.8 1.0Neutral n-regionNeutral p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. Reverse biasNeutral n-regionNeutral
13、 p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. Reverse biasWoxe(Vo+Vr)eVoW(V= -Vr)MHolePE(x)Reverse biased pn junction. (b) Hole PE across the junc
14、tion under reverse biasNeutral n-regionNeutral p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. Reverse biaspositiveNeutral n-regionNeutral p-regionxW
15、HolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. Neutral n-regionNeutral p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority Carrier
16、ConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. Neutral n-regionNeutral p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and
17、the origin of the reverse current. Neutral n-regionNeutral p-regionxWHolesElectronsDiffusionDriftThermallygeneratedEHPpnonpoEo+EVrMinority CarrierConcentrationWoReverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current. (a) Reverse I-V characteristics of a pn ju
18、nction (the positive and negative current axes have different scales). Ideal diodeSpace charge layergeneration, surface leakagecurrent, etc.VnAImA(a)(a) Reverse I-V characteristics of a pn junction (the positive and negative current axes have different scales). Ideal diodeSpace charge layergeneratio
19、n, surface leakagecurrent, etc.VnAImA(a)Jgen increases with Vr because W increases with Vr4.2 pn Junction Band DiagramEcEvEFnnn-Type SemiconductorEFppCBp-Type SemiconductorVBVBCBEcEvEg(a) Two isolated p and n-type semiconductors (same material). (b) A pn junctionband diagram when the two semiconduct
20、ors are in contact. The Fermi level must beuniform in equilibrium. The metallurgical junction is at M. The region around Mcontains the space charge layer (SCL). On the n-side of M, SCL has the exposedpositively charged donors whereas on the p-side it has the exposed negativelycharged acceptors.MpnEo
21、MBulkEcEvEFnEcEvDonors in SCLAcceptors in SCLEFpeVo=p-n4.2 pn Junction Band DiagramEcEvEFnnn-Type SemiconductorEFppCBp-Type SemiconductorVBVBCBEcEvEg(a) Two isolated p and n-type semiconductors (same material). (b) A pn junctionband diagram when the two semiconductors are in contact. The Fermi level
22、 must beuniform in equilibrium. The metallurgical junction is at M. The region around Mcontains the space charge layer (SCL). On the n-side of M, SCL has the exposedpositively charged donors whereas on the p-side it has the exposed negativelycharged acceptors.MpnEoMBulkEcEvEFnEcEvDonors in SCLAccept
23、ors in SCLEFpeVo=p-n4.2 pn Junction Band DiagramEcEvEFnnn-Type SemiconductorEFppCBp-Type SemiconductorVBVBCBEcEvEg(a) Two isolated p and n-type semiconductors (same material). (b) A pn junctionband diagram when the two semiconductors are in contact. The Fermi level must beuniform in equilibrium. The
24、 metallurgical junction is at M. The region around Mcontains the space charge layer (SCL). On the n-side of M, SCL has the exposedpositively charged donors whereas on the p-side it has the exposed negativelycharged acceptors.MpnEoMBulkEcEvEFnEcEvDonors in SCLAcceptors in SCLEFpeVo=p-n4.2 pn Junction
25、 Band DiagramEcEvEFnnn-Type SemiconductorEFppCBp-Type SemiconductorVBVBCBEcEvEg(a) Two isolated p and n-type semiconductors (same material). (b) A pn junctionband diagram when the two semiconductors are in contact. The Fermi level must beuniform in equilibrium. The metallurgical junction is at M. Th
26、e region around Mcontains the space charge layer (SCL). On the n-side of M, SCL has the exposedpositively charged donors whereas on the p-side it has the exposed negativelycharged acceptors.MpnEoMBulkEcEvEFnEcEvDonors in SCLAcceptors in SCLEFpeVo=p-n4.2 pn Junction Band DiagramMpnEoMBulkEcEvEFnEcEvD
27、onors in SCLAcceptors in SCLEFpeVo=p-n4.2 pn Junction Band DiagramMpnEoMBulkEcEvEFnEcEvDonors in SCLAcceptors in SCLEFpeVo=p-nForwardbiasVInpEo-Ee(Vo-V)eVEcEFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)ForwardbiasVInpEo-Ee(Vo-V)eVEcEFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)ForwardbiasVInpEo-Ee(Vo-V)eVEc
28、EFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)ForwardbiasVInpEo-Ee(Vo-V)eVEcEFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)ForwardbiasVInpEo-Ee(Vo-V)eVEcEFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)ForwardbiasVInpEo-Ee(Vo-V)eVEcEFnEvEvEcEFp(b)EcEvEcEFpMEFneVopnEoEvnp(a)Energy band diagrams for a pn junction und
29、er (c) reverse bias conditions. Reverse biasEnergy band diagrams for a pn junction under (c) reverse bias conditions. Reverse biasReverse biasEnergy band diagrams for a pn junction under (d) Thermal generation of electron hole pairs in the depletion region results in a small reverse current.Reverse
30、biasEnergy band diagrams for a pn junction under (d) Thermal generation of electron hole pairs in the depletion region results in a small reverse current.4.3 Bipolar Transistorpn(0)pn(x)pnoWEBWBCWBnponp(0)EICIEIBxBVCBVEBnp(x)E(b)Cp+np(a)EmiterBaseCollectorICIE(a) A schematic illustration of the pnp
31、bipolar transistor with three differently doped regions. (b) The pnp bipolar operated under normal and active conditions.4.3 Bipolar Transistor4.3 Bipolar Transistor4.3 Bipolar Transistor(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and a
32、ctive conditions.Fig. (c) shows the CB transistor circuit with the BJT represented by its circuit symbol. The arrow identified the emitter junction and points in the direction of current flow when the EB junction is forward biased. Fig. (c) also identifies the emitter circuit, where VEB is connected
33、, as the input circuit. The collector circuit, where VCB is connected, is the output circuit. (c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pn
34、p bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and acti
35、ve conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration w
36、ith input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified
37、(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under norma
38、l and active conditions.(c) The CB configuration with input and output circuits identified(b) The pnp bipolar operated under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditi
39、ons.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditi
40、ons.In t, a(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active
41、conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active
42、conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.(b) The pnp bipolar operated under normal and active conditions.(d) The illustration of various current components under normal and active conditions.
