# Where does forward voltage drop in a diode?

To simplify the picture, I would start with an n-type Schottky diode. It has two junctions: one rectifying and one non-rectifying (ohmic contact).

When the diode is forward biased, it conducts current, but it has a small voltage drop, say, 0.3V. Most, if not all, textbooks will tell you that this voltage drops on the rectifying junction.

To me, it seems more likely that the forward voltage drops on the ohmic contact. Has anyone personally measured the voltage drop on the rectifying junction? If not, can anyone suggest how it can be done (if it can be done)?

The same question is applicable to p-n junction diodes.

• Draw the band diagram through the diode. Why is the ohmic contact taking the voltage drop across the depletion region? (Now, there will be ohmic voltage drops in the $n$ and $p$ portions away from the junction itself, just from the material resistivity.) – Jon Custer Mar 18 '18 at 20:50
• Making good ohmic contacts to a solid state diode is indeed an important detail in the real world manufacturing of diodes, and one which I believe has been effectively dealt with. The textbooks you're reading are just focussing on the physics of the junction itself. – user93237 Mar 18 '18 at 21:14
• I am not talking about resistive voltage drop. I am talking about the forward voltage drop. The textbooks assume that the ohmic contact has very low resistance in both directions and don't bother to include it in the band diagrams, as if it was just a metal-to-metal contact. So, I am supposed to believe that the forward voltage drop occurs on the forward biased junction. Perhaps. But is it possible to prove by direct measurements? If not, I can speculate that the voltage drop occurs on the ohmic contact: after all, for a forward biased Schottky, the ohmic contact is reverse biased. – V.F. Mar 18 '18 at 21:42
• Not an expert on metal-semiconductor contacts, but I thought that Schottky contacts and ohmic contacts are different types of contacts, with Schottky contacts being rectifying and non-ohmic (since ohmic contacts should show symmetric current behavior under voltage reversal). So, according to my knowledge and recollection, I don't think that true ohmic contacts are ever reverse biased. – user93237 Mar 18 '18 at 21:57
• "Not all metal–semiconductor junctions form a rectifying Schottky barrier; a metal–semiconductor junction that conducts current in both directions without rectification, perhaps due to its Schottky barrier being too low, is called an ohmic contact." en.wikipedia.org/wiki/Schottky_barrier – user93237 Mar 18 '18 at 22:14