From: mustafa@seas.smu.edu (Mustafa Kocaturk)
Subject: Re: The Theories are Full of Holes
Summary: Electron holes exist in semiconductors
Keywords: electrons, holes, resistance, superconductors
Cc: mustafa
Organization: SMU - School of Engineering & Applied Science - Dallas
Date: Wed, 23 Dec 1992 20:10:40 GMT

In article <BzK6I4.CuM@csn.org> et@teal.csn.org (Eric H. Taylor) writes:
>                    THE THEORIES ARE FULL OF HOLES
>                                or
>                  IS RESISTIVE HEATING A GAS EFFECT?
>
>It is common knowledge that an electric current thru a resistor causes heating.
>But why?
>Consider: most currents are cause by increased pressure. Normally, we cause
>a current by "pushing" the electrons thru a conductor. Since electrons are
>a gas, like with any gas, as pressure is increased, so does temperature
>increase. The usual explanation of resistive heating is that collisions
>of electrons with nuclei increases the temperature due to friction. I claim
>instead that the temperature rise is due to increasing the pressure of the
>electron gas, and the conductor is heated via a thermal heat transfer.

  Would this line of reasoning not entail that a charged capacitor
  should be hotter than a resistor that is used to discharge it ? :-)

>
>This concept gets very interesting when you consider the effect of running
>an electron hole current thru a conductor. An electron hole is the
>absence (instead of presence) of an electron. The electrical properties of
>a hole are identical to electrons, except that they "move" positive charge
>instead of negative charge. Realizing that a hole current would represent
>a decreased pressure, the temperature of the electrons would decrease.
>Again, as thermal transfer, the temperature of the conductor would also
>decrease.

  Holes have an equivalent mass and momentum.  In their interactions with
  the crystal lattice, their momenta can be partly transferred
  to the crystal lattice, giving off energy in the form of heat
  (indirect semiconductors as in ordinary diodes), or they can transfer
  all their momenta to the lattice structure in one shot, with photons
  being released (direct semiconductors as in light-emitting diodes).
  It would be too bold to assert that no heat is generated
  in practical LED's, that would mean that 100% of the energy, VxI,
  of an LED is converted to light.  The actual quantum efficiency
  of an LED is much less.

  I would prefer not to speak about holes in metals,
  but about an electron gas, since metals have no energy gap.

  The pressure analogy for resistive heat is more appropriate in an
  electrostatic context rather than an electrodynamic one, and it is
  far from being semantically sound.  Forcing
  current through a conductor is work done against friction.
  Injecting holes in the same direction as electrons would
  tend to reduce the current, thus reducing the heat dissipated in
  the resistor.  Injecting holes opposite the flow of electrons
  would assist the total current.  The total charge in the conductor
  cannot rise beyond CxV, therefore, in the long run, as many
  electrons are removed from the conductor as are pumped into it.
  
  A temperature drop would occur in an electronic heat pump using
  thermocouples or semiconductor junctions.  Still, that would require
  spending extra energy somewhere else such that the total entropy
  of the system is not reduced.

>So the primary questions are how should we modify the basic electrical
>calculations of voltage and resistive effects under conditions of large
>hole currents?

  There is no need for such a modification, because a hole current is
  mainly an equivalent flow of valence electrons in the opposite
  direction.  This means that the electrons will still be in motion,
  exchanging energy with the crystal lattice, but at a different
  quantum band of levels.

>
>For example, heat transfer is given as I^2*R. Should this be rewritten
>to be (In - Ip)^2*R? [Where In is the electron current, and Ip is the
>hole current] Would the total current be |In| + |Ip|? If a large hole
>current was run thru an incandescent light bulb, how would the spectrum
>change?

  In an incandescent lamp, the charge carriers are electrons (or positrons,
  in an anti-matter world).  What sense does it make to speak of
  holes or anti-holes in metals, when everybody knows that in a *metal*
  at that temperature, no energy gap exists between the valence band
  nd the conduction band of electron quantum states?  The term "hole"
  attains most of its significance in the study of semiconductors,
  which have a nonzero energy gap.

>
>Can you design electrical circuits that would amplify holes preferentially
>over electrons? Or how about a circuit that discriminates (and separates)
>hole currents from electron currents? In other words, how would you design
>an experiment to test the above equation (In - Ip)^2*R?
>

  This equation can be tested inside semiconductors. Actually,
  In and Ip are proportional to their respective charge carrier
  densities and mobilities, and by convention, we add them rather
  than subtract, that is, the total current I=Ip+In, and
  this does not contradict the fact that the *particle* flow of
  electrons is opposite the electric field vector, whereas that of
  holes is in the same direction with it.

  As to amplifying currents of one kind only, it is done by selecting
  the type of semiconductor to use as the amplifying device.  In an
  NMOS enhancement FET, for example, electrons are amplified, whereas,
  in a PMOS enhancement FET, holes are.
  
  The impact of this choice on the final result
  is in terms of speed, power, fan-out, and technical complexity.
  Rarely do we need to know what type of carrier is amplified
  when we are using a computer that consists mainly of CMOS LSI's.

>High temperature superconductors are ceramic semi-conductors at normal
>temperatures. Does anyone have data on electron and hole mobilities in
>various high temperature superconductors, both at room temperature, and
>at superconductive temperatures?
>
>----
> ET   "A Force of Nature"
>----

I, too, am interested in the quantum electrodynamics of superconductors.

Yours respectfully,

Mustafa

-- 
Mustafa Kocaturk   mustafa@seas.smu.edu  EE Dept., Room 305A, Caruth Bldg.
Home: 214-706-5954  Office: 214-768-1475  SMU Box 753190, Dallas, TX 75275
    (-: No wonder why high-voltage lines are said to be "hot" :-)

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