Hole: Fictitious positive charge representing the motion of electrons in the valence band of a semiconductor; the number of holes equals the number of unoccupied quantum states in the valence band. Phonon: Quantum of lattice vibration. Photon: Quantum of electromagnetic radiation Related Topic 52.1 Introduction References D K. Ferry, Semiconductors, New York: Macmillan, 1991 Y Okuto and C.R. Crowell, Phys. Rev, vol. B6, P 3076, 1972. K von Klitzing, Rev. Modern Phys, vol 58, P 519, 19 s5s, N./. Prentice-Hall, 19 g R F. Pierret, Advanced Semiconductor Fundamentals, Reading, Mass.: Addison-Wesley, 1987 C M. Wolfe, N. Holonyak, and G.E. Stilman, Physical Properties of Semiconductors, Englewood Cliffs, N J: Prentice-Hall, 1989 Further Information Engineering aspects of semiconductor physics are often discussed in the IEEE Transactions on Electron Devices, Journal of applied Physics, and Solid-State Electronics. 22.2 Diodes Miran Ilkovic Diodes are the most widely used devices in low- and high-speed electronic circuits and in rectifiers and power upplies. Other applications are in voltage regulators, detectors, and demodulators Rectifier diodes are capable of conducting several hundred amperes in the forward direction and less than 1 HA in the reverse direction. Zener diodes are ordinary diodes operated in the Zener or avalanche region and are used as voltage regulators Varactor diodes are ordinary diodes used in reverse biasing as voltage-dependent capacitors. Tunnel diodes and quantum well devices have a negative differential resistance and are capable of operating in the upper gigahertz region. Photodiodes are ordinary diodes operated in the reverse direction. They are sensitive to light and are used as light sensors. Solar cells are diodes which convert light energy into electrical energy. Schottky diodes, also known as metal-semiconductor diodes, are extremely fast because they are majority carrier devices pn- unction Diode A pn-diode is a semiconductor device having a p-region, a n-region, and a junction between the regions. Modern planar semiconductor pn-junction diodes are fabricated by diffusion or implantation of impurities into a semiconductor. An n-type semiconductor has a relatively large density of free electrons to conduct electric current, and the p-type semiconductor has a relatively large concentration of"free"holes to conduct electric current. The pn-junction is formed during the fabrication process. There is a large concentration of holes in the p-semiconductor and a large concentration of electrons in the n-semiconductor. Because of their large concentration gradients, holes and electrons start to diffuse across the junction. As holes move across the junction, negative immobile charges(acceptors)are uncovered on the p side, and positive immobile charges (donors)are uncovered on the n side due to the movement of electrons across the junction. When sufficient numbers of the immobile charges on both sides of the junction are uncovered, a potential energy barrier voltage lo is created by the uncovered acceptors and donors. This barrier voltage prevents further diffusion of holes and electrons across the junction. The charge distribution of acceptors and donors establishes an opposing e 2000 by CRC Press LLC© 2000 by CRC Press LLC Hole: Fictitious positive charge representing the motion of electrons in the valence band of a semiconductor; the number of holes equals the number of unoccupied quantum states in the valence band. Phonon: Quantum of lattice vibration. Photon: Quantum of electromagnetic radiation. Related Topic 52.1 Introduction References D.K. Ferry, Semiconductors, New York: Macmillan, 1991. Y. Okuto and C.R. Crowell, Phys. Rev., vol. B6, p. 3076, 1972. R.F. Pierret, Advanced Semiconductor Fundamentals, Reading, Mass.: Addison-Wesley, 1987. M. Shur, Physics of Semiconductor Devices, Englewood Cliffs, N.J.: Prentice-Hall, 1990. K. von Klitzing, Rev. Modern Phys., vol. 58, p. 519, 1986. C.M. Wolfe, N. Holonyak, and G.E. Stilman, Physical Properties of Semiconductors, Englewood Cliffs, N.J.: Prentice-Hall, 1989. Further Information Engineering aspects of semiconductor physics are often discussed in the IEEE Transactions on Electron Devices, Journal of Applied Physics, and Solid-State Electronics. 22.2 Diodes Miran Milkovic Diodes are the most widely used devices in low- and high-speed electronic circuits and in rectifiers and power supplies. Other applications are in voltage regulators, detectors, and demodulators. Rectifier diodes are capable of conducting several hundred amperes in the forward direction and less than 1 mA in the reverse direction. Zener diodes are ordinary diodes operated in the Zener or avalanche region and are used as voltage regulators. Varactor diodes are ordinary diodes used in reverse biasing as voltage-dependent capacitors. Tunnel diodes and quantum well devices have a negative differential resistance and are capable of operating in the upper gigahertz region. Photodiodes are ordinary diodes operated in the reverse direction. They are sensitive to light and are used as light sensors. Solar cells are diodes which convert light energy into electrical energy. Schottky diodes, also known as metal-semiconductor diodes, are extremely fast because they are majority carrier devices. pn-Junction Diode A pn-diode is a semiconductor device having a p-region, a n-region, and a junction between the regions. Modern planar semiconductor pn-junction diodes are fabricated by diffusion or implantation of impurities into a semiconductor. An n-type semiconductor has a relatively large density of free electrons to conduct electric current, and the p-type semiconductor has a relatively large concentration of “free” holes to conduct electric current. The pn-junction is formed during the fabrication process. There is a large concentration of holes in the p-semiconductor and a large concentration of electrons in the n-semiconductor. Because of their large concentration gradients, holes and electrons start to diffuse across the junction. As holes move across the junction, negative immobile charges (acceptors) are uncovered on the p side, and positive immobile charges (donors) are uncovered on the n side due to the movement of electrons across the junction. When sufficient numbers of the immobile charges on both sides of the junction are uncovered, a potential energy barrier voltage V0 is created by the uncovered acceptors and donors. This barrier voltage prevents further diffusion of holes and electrons across the junction. The charge distribution of acceptors and donors establishes an opposing