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 JunctionsGeSiGaAsCurrentVoltage0.1 mA0 0.2 0.4 0.6 0.8 1.0
