《半导体材料与技术》chapter4-3.ppt
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1、Chapter 4 Semiconductor devices,4.1 Ideal pn junction 4.2 pn Junction Band Diagram 4.3 Bipolar Transistor 4.4 Junction Field Effect Transistor 4.5 Metal Oxide Semiconductor Field Effect Transistor 4.6 Light Emitting Diodes 4.7 Solar Cells,From Principles of electronic Materials Devices, SO Kasap (Mc
2、Graw-Hill, 2005),4.1 Ideal pn junction,4.1 Ideal pn junction,4.1 Ideal pn junction,4.1 Ideal pn junction,4.1 Ideal pn junction,4.1 Ideal pn junction,Considering an abrupt pn junction: net(x) can simply be described by step functions shown in Fig. (d). Using the step form of net(x) in Fig. (d) in the
3、 integration of gives the electric field at M.,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 width of the depletion region under a zero applied voltage.,The simplest way to relate V0 to the doping parameters i
4、s to make use of the fact that in the system consisting of p- and n- type semiconductors joined together, in equilibrium, Blotzmann statistics demands that the concentrations n1 and n2 of carriers at potential energies E1 and E2 are related by,Considering electrons (q=-e), we see from Fig. (g) that
5、E=0 on the p side far away from M where n=npo, and E=-eVo on the n-side away from M where n=nno. Thus,Which mean that Vo depends on nno and npo and hence on Nd and Na. The corresponding equation for hole concentrations is clearly,Rearranging And We obtain We can now write ppo and pno in terms of the
6、 dopant concentrations inasmuch as ppo=Na and,Forward bias: diffusion current,Forward bias: diffusion current,Forward bias: diffusion current,(b),Forward bias: diffusion current,(b),Forward bias: diffusion current,Law of the junction is an important equation that we,(b),Forward bias: diffusion curre
7、nt,(b),Forward bias: diffusion current,(b),Forward bias: diffusion current,(b),Forward bias: diffusion current,(b),Forward bias: diffusion current,Reverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current.,Reverse bias,Reverse biased pn junction. (a) Minority ca
8、rrier profiles and the origin of the reverse current.,Reverse bias,Reverse biased pn junction. (b) Hole PE across the junction under reverse bias,Reverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current.,Reverse bias,positive,Reverse biased pn junction. (a) Min
9、ority carrier profiles and the origin of the reverse current.,Reverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current.,Reverse biased pn junction. (a) Minority carrier profiles and the origin of the reverse current.,Reverse biased pn junction. (a) Minority car
10、rier profiles and the origin of the reverse current.,(a) Reverse I-V characteristics of a pn junction (the positive and negative current axes have different scales).,(a) Reverse I-V characteristics of a pn junction (the positive and negative current axes have different scales).,Jgen increases with V
11、r because W increases with Vr,4.2 pn Junction Band Diagram,4.2 pn Junction Band Diagram,4.2 pn Junction Band Diagram,4.2 pn Junction Band Diagram,4.2 pn Junction Band Diagram,4.2 pn Junction Band Diagram,Forward bias,Forward bias,Forward bias,Forward bias,Forward bias,Forward bias,Energy band diagra
12、ms for a pn junction under (c) reverse bias conditions.,Reverse bias,Energy band diagrams for a pn junction under (c) reverse bias conditions.,Reverse bias,Reverse bias,Energy band diagrams for a pn junction under (d) Thermal generation of electron hole pairs in the depletion region results in a sma
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