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Conceptual Physics
Study Notes & Questions: Semiconductors (Chap. 25)
1)
Pure semiconductors are good insulators, although some thermally
induced conductivity occurs. Their valance electrons’ orbitals almost,
but not quite, mix with neighboring atoms (which would allow currents
to flow.) However if tiny amounts of alternative atoms are introduced
into the semiconductor crystal, their valence orbitals do mix enough to
allow current to flow. This is called doping (p532).
2)
In n-type semiconductors, electrons carry current. In p-type
semiconductors, holes—that is valence orbital vacancies—can
perform the same function as carrying current. (p532).
3)
Diodes are formed when n-type and p-type semiconductors are
placed adjacent to one another. At the contact surface, electrons and
holes, forming a depletion zone that has a small electric field across
it, allow electrons to cross from n-to-p but not p-to-n. (NOTE: the
current flow direction is actually in the opposite direction of electron
flow.)
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4)
A diode rectifies AC current, only allowing current to flow in one
direction (p534).
5)
A transistor is a sandwich of p, n & p (or n, p & n) semiconductors.
Normally, this construction is insulating—a voltage placed across the
two end plates will not flow. A small metal electrode placed above the
center material injects extra electrons in the center semiconductor
which dramatically changes its conduction properties. Current now
flows freely between the two end plates. By adjusting the center
electrode voltage up and down, the large current between the two end
plates can be adjust up and down. (p535)
6)
In computer language, a bit is a “quantum of information.” In a
physical system, like an integrated circuit (p538), a bit is a high or low
voltage at a particular electrode position, at a particular moment in
time. (p540). In a magnetic data storage medium, a bit of data is
stored as a particular orientation of a magnetic field in a small patch
of surface material. (p544)
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