Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 26/09/2012 16:30:01

Title: How do holes carry heat?
Post by: thedoc on 26/09/2012 16:30:01

Tony Chang  asked the Naked Scientists:
   
If movement of holes results from electrons moving in the opposite direction,how do holes carry heat away in the p-type semiconductor?

If one side of the p-type semiconductor is heated, does the heat move from lattice vibration? If true, then heat would move regardless of the hole movement?

I did a lot of searching on internet, but I couldn't get an answer.

Thank you very much.

Sincerely,
Tony Hue
   
What do you think?

Title: Re: How do holes carry heat?
Post by: evan_au on 30/09/2012 12:49:22

When an electrical current flows in a P-Type semiconductor, a flow of holes can be viewed as "electrons moving in the other direction". However, it is equally valid to treat the hole as a virtual particle in its own right, generally with a different effective mass and velocity than an electron subject to the same electric field.

In the absence of an electric or thermal gradient:

• At any temperature above absolute zero, random thermal motion of the atoms in a semiconductor propagates as phonons, in random directions.
• At the normal operating temperature of a semiconductor, random thermal motion kicks some electrons & holes into the conduction band, where they can diffuse in random directions.
• The phonons scatter off charge carriers: electrons (in N-Type semiconductors) or holes (in P-Type), see http://en.wikipedia.org/wiki/Electron_mobility#Lattice_.28phonon.29_scattering
• And so heat in a P-Type semiconductor is carried by a mixture of phonons & holes, see http://en.wikipedia.org/wiki/Electron_mobility#Temperature_dependence_of_mobility

The phonons & holes interact in a more direct way when voltage or thermal gradients appear:

• When a temperature difference is applied across a semiconductor, the phonons sweep the hot charge carriers (holes or electrons) from the hot side to the cold side, creating a voltage. This is used in thermoelectric generators: http://en.wikipedia.org/wiki/Thermoelectric_effect#Charge-carrier_diffusion
• When a voltage difference is applied across a semiconductor, the charge carriers (holes or electrons) drift due to the voltage, sweeping up the phonons and creating a temperature difference. This is used in Peltier-junction coolers: http://en.wikipedia.org/wiki/Thermoelectric_effect#Peltier_effect

Title: Re: How do holes carry heat?
Post by: yor_on on 01/10/2012 14:47:56

Phonon's are fascinating Evan. Been reading about superconductivity, in where the explanation to it becomes one of electrons, arranging themselves into Cooper pairs, overcoming their repulsion due to temperature and type of material. And what binds those electrons, carrying superconductivity, is phonon's. Small quantized 'packets' of 'vibrational energy'. The really interesting thing about them, to me, is that they reminds me so much of  photons, although in lattices as in a crystal.
=

Although I once again find this 'virtuality' being used to describe the process :)
It should be describable from a indeterministic state treating a Cooper pair as 'one thing' too, as I think? Especially as the coherence/influence of them are macroscopic.

"Careful examination of the boundary shows that it results from the long range of influence of the superconducting electrons over a macroscopic distance of about 10^–4 cm., which is the coherence length."