3
\$\begingroup\$

Ohm's law is valid for metals, but is it valid for semiconductors? Does it work there?

I am not talking about a PN junction here.

If I have a block of silicon and pass voltage across it, will I see current flowing, in accordance with Ohm's law?

\$\endgroup\$
  • \$\begingroup\$ Yes. In fact, the very first chapter of any book on microelectronics starts out at the beginning analyzing semiconductor behavior with the assumption of the Drude model and the application of Ohm's Law (though you'd have to put some of the equations together to produce Ohm's law, since they will be using volts/meter, usually.) \$\endgroup\$ – jonk Apr 27 at 14:02
  • 1
    \$\begingroup\$ You would need a block of silicon doped with either a N-type or P-type to make it a conductor. Silicon on it's own wouldn't conduct current because there is no transfer of electrons/holes. \$\endgroup\$ – Rajesh S Apr 27 at 16:24
  • \$\begingroup\$ The relationship between voltage, current, and resistance always applies; the confusing parts are situations where these have interdependence, such that the effective resistance at one voltage or current is different from that at another. But the relationship between those in any given situation holds. \$\endgroup\$ – Chris Stratton Apr 27 at 17:55
  • 1
    \$\begingroup\$ @RajeshS Pure silicon is still conductive, just much less so. \$\endgroup\$ – Hearth Apr 27 at 17:55
  • 4
    \$\begingroup\$ Possible duplicate of Does a diode really follow Ohm's Law? \$\endgroup\$ – vaxquis Apr 27 at 21:29
8
\$\begingroup\$

Yes. All materials under normal conditions and at fixed temperature follow* ohm's law, though it becomes less useful in good insulators where breakdown occurs before any substantial amount of current can flow.

Non-ohmic effects occur at boundaries between different materials, such as pn junctions, schottky junctions, thermocouples, electrochemical cells, et cetera. They can also be observed in discharge phenomena, where the flow of current causes ionization and chemical changes in the conducting material.

*Here, "follow" means "behave in a way closely approximated by". Depending on how precisely you're measuring things, it may matter that it's not quite exact.

Edit: it's worth mentioning that the presence of (changing) magnetic fields can complicate things. Transformers and inductors are not generally considered to obey ohm's law under dynamic conditions, for instance.

For further information on where it gets murky, see this question.

\$\endgroup\$
  • 2
    \$\begingroup\$ To be accurate, I'd phrase it "nearly all materials under normal conditions closely approximate Ohm's law". As engineers, we tend to separate the exceptions into nicely explained phenomena, such as resistance change due to heating, or thermoelectric effects, or rectification, etc., etc., etc. If you're going into a 16-bit ADC, then in general you only just barely start to worry. If you're going into a 24-bit ADC and the last eight aren't just there to boost your ego, then worry. \$\endgroup\$ – TimWescott Apr 27 at 16:29
  • 1
    \$\begingroup\$ Velocity saturation... \$\endgroup\$ – sstobbe Apr 27 at 17:39
  • \$\begingroup\$ @sstobbe Would you consider velocity saturation to be "under normal conditions"? \$\endgroup\$ – Hearth Apr 27 at 17:42
  • \$\begingroup\$ @TimWescott Good point. I'll add that note. \$\endgroup\$ – Hearth Apr 27 at 17:42
  • \$\begingroup\$ I guess normal is relative to application. Certainly agree ohms law always is true in differential form \$\endgroup\$ – sstobbe Apr 27 at 18:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.