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Chapter 1: Q29E (page 1)
Obtain the smoothness conditions at the boundaries between regions for the barrier (i.e., tunneling) case.
The four conditions that are boxed above are the smoothness condition for the given condition.
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71. In many kinds of integrated circuits. the preferred element of amplification/switching is nor the bipolar transistor discussed in the chapter, but the MOSFET (metal oxide semiconductor field effect transistor). Thecompany diagram shows one in its "normally off" state: Conduction electrons cannot flow from the n-type source, which is analogous to the emitter. "over the bump" in the ptype region to the n-type drain. analogous to the collector. (Annpn arrangement is shown. but just as for the bipolar transistor, a pnp would yield the complementary device.) The important difference is that rather than a direct electrical contact to the p-type region, as in the base of the bipolar, the centre lead, the gate, is a conductor bonded to the p-type region but separated by a thin insulating layer.
(a) Explain how applying a bias to the gate can cause this device to tum on. Should the gate bias voltage be positive or negative (relative to the source)? Why is the control mechanism referred to as "field effect"?
(b) The MOSFET is often said to be a "unipolar" device because valence holes (conduction elections in the pnp device) do not play the important role that they do in the bipolar. Explain. Would you expect a significant current through the gate due to electron-hole recombination in the p-type region? Why or why not?
(c) A low-input-impedance device is one in which there are large oscillations in input current for small oscillations in the input voltage. Correspondingly, a highinput-impedance device has a small input currentfor a large input voltage. Bearing in mind that the voltage across the forward-biased base-emitter diode of a bipolar transistor is always about , while the input current is proportional to the output current, would you say that the bipolar transistor has low or high input impedance? What about the MOSFET?
Estimate characteristic X-ray wavelengths: A hole has already been produced in the n=1 shell, and an n=2 electron is poised to jump in. Assume that the electron behaves as though in a "hydrogenlike" atom (see Section 7.8), with energy given by . Before the jump, it orbits Z protons, one remaining electron. and (on average) half its seven fellow n=2 electrons, for a of . After the jump, it orbits Z protons and half of its fellow electron, for a of . Obtain a formula for versus Z . Compare the predictions of this model with the experimental data given in Figure and Table .
A signal is described by the function .
(a) Calculate the Fourier transform . Sketch and interpret your result.
(b) How are and affected by a change in t ?
A function is nonzero only in the region of width centered at
where C is a constant.
(a) Find and plot versus the Fourier transform of this function.
(b) The function ) might represent a pulse occupying either finite distance (localid="1659781367200" position) or finite time (time). Comment on the wave number if is position and on the frequency spectrum if is time. Specifically address the dependence of the width of the spectrum on .
A supersonic: - plane travels al . As this plane passes two markers a distance of apart on the ground, how will the time interval registered on a very precise clock onboard me plane differ from ?
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