Page 453 - Schaum's Outline of Theory and Problems of Applied Physics

438 THE SOLID STATE [CHAP. 35

In a metal oxide semiconductor field-effect transistor (MOSFET), the semiconductor gate is replaced by a metal
film separated from the channel by an insulating layer of silicon dioxide. The metal film is thus capacitively coupled
to the channel, and its potential controls the drain current through the number of induced charges in the channel. A
MOSFET is easier to make than the field-effect transistor of Fig. 35-12 and occupies only a few percent of the area
needed for a junction transistor.

Multiple-Choice Questions

35.1. Solids held together by van der Waals bonds usually
(a) have low melting points
(b) have high melting points
(c) are good conductors of electricity
(d) are extremely hard

35.2. The electron “gas” in a metal is not directly responsible for its
(a) electrical conductivity (c) surface luster
(b) thermal conductivity (d) strength

35.3. When the upper energy band of a solid is partly filled with electrons, the solid is
(a) an insulator (c) an n-type semiconductor
(b) a conductor (d) a p-type semiconductor

35.4. When a wide forbidden band in a solid separates an empty upper energy band from a filled lower band, the solid is
(a) an insulator (c) an n-type semiconductor
(b) a conductor (d) a p-type semiconductor
35.5. When an empty energy band in a solid has occupied donor levels below it, the solid is
(a) an insulator (c) an n-type semiconductor
(b) a conductor (d) a p-type semiconductor
35.6. A hole in a p-type semiconductor is which one or more of the following?

(a) a missing atom
(b) a missing electron
(c) equivalent to a positive charge
(d) equivalent to a negative charge
35.7. A current in a p-type semiconductor involves the motion of

(a) electrons (c) positive atomic ions
(b) holes (d) negative atomic ions

35.8. A current in an n-type semiconductor involves the motion of
(a) electrons (c) positive atomic ions
(b) holes (d) negative atomic ions

35.9. A junction between n- and p-type semiconductors conducts electric current best when
(a) both ends are positive
(b) both ends are negative
(c) the p end is positive and the n end is negative
(d) the p end is negative and the n end is positive