Physics Assignments

TRANSISTORS

TRANSISTORS A bipolar junction transistor includes two p-n junctions in a “sandwich” configuration, which may be either p-n-p or n-p-n. Such a p-n-p transistor is shown in Fig. 44-31. The three regions are called the emitter, base, and collector, as shown. When there is no current in the left loop of the circuit, there is only a very …

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SEMICONDUCTOR DEVICES

SEMICONDUCTOR DEVICES Semiconductor devices play an indispensable role in contemporary electronics. In the early days of radio and television, transmitting and receiving equipment relied on vacuum tubes, but these have been almost completely replaced in the last three decades by solid-state devices, including transistors, diodes, integrated circuits, and other semiconductor devices. The only surviving vacuum tubes in radio and …

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IMPURITIES

IMPURITIES Suppose we mix into melted germanium (Z = 32) a small amount of arsenic.(Z = 33), the next element after germanium in the periodic table. This deliberate addition of impurity elements is called doping. Arsenic is in Group V; it has five valence electrons. When one of these electrons is removed, the remaining electron structure is essentially …

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SEMICONDUCTORS

SEMICONDUCTORS A semiconductor has an electrical resistivity that is intermediate between those of good conductors and of good insulators. The tremendous importance of semiconductors in present-day electronics stems in part from the fact that their electrical properties are very sensitive to very small concentrations of impurities. We’ll discuss the basic concepts using the semiconductor elements silicon (Si) and germanium …

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SUPERCONDUCTIVITY

SUPERCONDUCTIVITY Superconductivity is the complete disappearance of all electrical resistance at low temperatures. We described this property at the end of Section 26-3 and the magnetic properties of type I and type II superconductors in Section 30-9. In this section we’ll relate superconductivity to the structure and energy-band model of a solid. Although superconductivity was discovered in 1911, it …

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HOLES

HOLES When an electron is removed from a covalent bond, it leaves a vacancy behind. An electron from a neighboring atom can move into this vacancy, leaving the neighbor with the vacancy. In this way the vacancy, called a hole, can travel through the material and serve as an additional current carrier. It’s like describing the motion of …

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FERMI-DIRAC DISTRIBUTION

FERMI-DIRAC DISTRIBUTION Now we need to know how the electrons are distributed among the various quantum states at any given temperature. The Maxwell-Boltzmann distribution states that the average number of particles in a state of energy E is proportional to e-EltT (page 1250). However, it wouldn’t be right to use the Maxwell-Boltzmann distribution, for two very important reasons. The …

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