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Lecture Electrical Engineering: Lecture 3 - Dr. Nasim Zafar

In this chapter, you will learn about: Generation and Recombination, thermal generation/excitation, optical generation/excitation, particle bombardment and other external sources. | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Generation and Recombination Lecture No: 3 Generation and Recombination 2 Generation- Processes: Thermal Generation/excitation. Optical Generation/excitation. Particle Bombardment and other External Sources Equilibrium and Generation/Recombination: So far, we have discussed the charge distributions in thermal equilibrium: The end result was np = ni2 When the system is perturbed, the system tries to restore itself towards equilibrium through recombination-generation. • We will calculate the steady-state rates. This rate will be proportional to the deviation from equilibrium, R = A(np-ni2). Generation and Recombination: In semiconductors, carrier generation and recombination are processes by which “mobile” charge carriers (electrons and holes) are produced and eliminated. Charge carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as: Photo Diodes LEDs and Laser Diodes. They are also critical to a full analysis of PN junctions devices such as Bipolar Junction Transistors et. Generation and Recombination: Generation = break up of covalent bonds to form electrons and holes; Electron-Hole Pair generation. Electron-Hole Pair generation requires energy in the following forms: Thermal Energy ( thermal generation/excitation) Optical (optical generation/excitation) or other external sources ( e.g. particle bombardment). Recombination = formation of bonds by bringing together electron and holes Releases energy in thermal or optical form A recombination event requires 1 electron + 1 hole The ease with which electrons in a semiconductor can be excited from the valence band to the conduction band depends on the band gap, and it is this energy gap that serves as an arbitrary dividing line ( 5 eV) between the semiconductors and insulators. In terms . | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Generation and Recombination Lecture No: 3 Generation and Recombination 2 Generation- Processes: Thermal Generation/excitation. Optical Generation/excitation. Particle Bombardment and other External Sources Equilibrium and Generation/Recombination: So far, we have discussed the charge distributions in thermal equilibrium: The end result was np = ni2 When the system is perturbed, the system tries to restore itself towards equilibrium through recombination-generation. • We will calculate the steady-state rates. This rate will be proportional to the deviation from equilibrium, R = A(np-ni2). Generation and Recombination: In semiconductors, carrier generation and recombination are processes by which “mobile” charge carriers (electrons and holes) are produced and eliminated. Charge carrier generation and recombination processes are .