Lecture_7_9 - Lecture 7-9 PN Junction Topics PN Junction in...

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Handout 2 ECE 315, Cornell University 1 PN Junction Topics PN Junction in equilibrium PN Junction in reverse bias PN Junction in forward bias Reading Assignment Sedra and Smith Chap 3 Howe Chap 3, Howe Chap 6 Sedra appendix A Lecture 7-9
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Handout 2 ECE 315, Cornell University 2 PN Junction The PN junction was the first pure semiconductor device made operational, prior to that the devices were metal-semiconductor By definition the PN junction is a device where the P region and the N region are in intimate contact The PN junction is present in virtually every semiconductor device-see next slides
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Handout 2 ECE 315, Cornell University 3 Diodes, Lateral BJT and BiCMOS pnp bipolar BiCMOS cross section Fig. A.7 Fig. A.9 Fig. A.8
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Handout 2 ECE 315, Cornell University 4 CMOS Cross Section LOCOS or shallow- trench isolation Junction isolation 1 1 2 2 body contact well contact Fig. A.3
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Handout 2 ECE 315, Cornell University 5 Electrostatics of PN Junction in Equilibrium Focus on intrinsic region Abrupt doping distribution
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Handout 2 ECE 315, Cornell University 6 Thought experiment: bring two pieces of semiconductor together. What happens to the carriers? Far from the junction nothing happens-called quasi neutral regions Around the junction currents of drift And diffusion must cancel- space charge region
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Handout 2 ECE 315, Cornell University 7 Depletion Approximation Assume quasi neutral regions perfectly neutral Assume space charge regions depleted of carriers Assume transition between space charge region and neutral region sharp
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Handout 2 ECE 315, Cornell University 8 Mathematical boundary conditions Space charge density
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Handout 2 ECE 315, Cornell University 9 Electric Field
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Handout 2 ECE 315, Cornell University 10 Built-in Potential in P-N Junction Diode Independent of the transition region, the P-side and N-side have a potential difference in equilibrium with respect to the same reference potential to the intrinsic silicon!!! n-type semiconductors: ( 29 D D o N N x n 2245 = + p-type semiconductors: ( 29 A A o N N x p 2245 = - ( 29 - = = - i A p kT x q i A n N q kT e n N p log φ φ = - = 2 ln i D A p n bi n N N q kT V φ φ ( 29 = = i D n kT x q i D n N q kT e n N n log φ φ Complete ionization at room temp.
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Handout 2 ECE 315, Cornell University 11 To get full potential curve integrate the field. Calculation of Electrostatic Potential
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Handout 2 ECE 315, Cornell University 12 Calculation of x po and x no
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Handout 2 ECE 315, Cornell University 13
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Handout 2 ECE 315, Cornell University 14
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Handout 2 ECE 315, Cornell University 15 The potential distribution derived so far implies That using a voltmeter we could measure a potential across a diode. A simple experiment will show that is not true
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Handout 2 ECE 315, Cornell University 16 In order for the device to communicate to the outside world metal contacts need to be added. These contacts form metal semiconductor junctions. The potential drop across these junctions causes the device terminals to operate at the same potential
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