An ohmic contact

[Moreno]

It is claimed that Schottky type of contact between low work function p-type semiconductor and higher work function metal creates an ohmic contact in which current can flow both sides almost fluently with very low resistance. It is also claimed that electrons have tendency to flow (when no potential is applied) from low work function material to higher work function material. So, when low work function p-type semiconductor comes in contact with higher work function metal, a p-type semiconductor will not let electrons from metal enter into semiconductors and will push them back. It seems a bit counterintuitive to me, because how in this case could it be an ohmic contact? Doesn't p-type semiconductor with lower work function suppose to cause resistance when potential is applied to make electrons flow from metal to semiconductor? Furthermore, if electrons penetrate from metal to p-type semiconductor under applied potential, doesn't they suppose to recombine with holes and create a depletion zone poor for any charge carriers and further increase resistance?

https://materion.com/-/media/files/advanced-materials-group/me/challenge-of-applying-ohmic-contacts.pdf

[studiot]

2 hours ago, Moreno said:

It is claimed that Schottky type of contact between low work function p-type semiconductor and higher work function metal creates an ohmic contact in which current can flow both sides almost fluently with very low resistance. It is also claimed that electrons have tendency to flow (when no potential is applied) from low work function material to higher work function material. So, when low work function p-type semiconductor comes in contact with higher work function metal, a p-type semiconductor will not let electrons from metal enter into semiconductors and will push them back. It seems a bit counterintuitive to me, because how in this case could it be an ohmic contact? Doesn't p-type semiconductor with lower work function suppose to cause resistance when potential is applied to make electrons flow from metal to semiconductor? Furthermore, if electrons penetrate from metal to p-type semiconductor under applied potential, doesn't they suppose to recombine with holes and create a depletion zone poor for any charge carriers and further increase resistance?

https://materion.com/-/media/files/advanced-materials-group/me/challenge-of-applying-ohmic-contacts.pdf

 

A Schottky barrier is high resistance in one direction and low resistance in the other.

An ohmic contact is low (ish) resistance in both directions.

They are not the same.

 

 

Quote

Moreno

It is claimed that Schottky type of contact between low work function p-type semiconductor and higher work function metal creates an ohmic contact in which current can flow both sides almost fluently with very low resistance.

Read your own reference again thoroughly.

 

Right at the beginning, it says the exact opposite of this

Quote

Materion

They can behave either as a Schottky barrier, or as an ohmic contact, depending on the characteristics of the interface.

 

Either a Sckottky barrier or an ohmic contact.

 

For your further information the Schottky barrier is formed when the metal is bonded directly to a block of intriniscally N or P type material.

This effect occurs with different metals for either N or P, but not both.

So bonding aluminium to N type  gold to P type creates the Schottky barrier.

Doing it the other way round does not.

 

Bonding the metal to a part of the block of N or P type material which is heavily doped to be even more N or P type creates an ohmic contact.

 

 

Whilst you are digesting this and asking further questions,  I will read the rest of your reference.

Edited March 18, 2019 by studiot

[Moreno]

5 hours ago, studiot said:

 

A Schottky barrier is high resistance in one direction and low resistance in the other.

An ohmic contact is low (ish) resistance in both directions.

They are not the same.

 

 

Read your own reference again thoroughly.

 

Right at the beginning, it says the exact opposite of this

 

Either a Sckottky barrier or an ohmic contact.

 

For your further information the Schottky barrier is formed when the metal is bonded directly to a block of intriniscally N or P type material.

This effect occurs with different metals for either N or P, but not both.

So bonding aluminium to N type  gold to P type creates the Schottky barrier.

Yes, read it carefully.

[studiot]

16 minutes ago, Moreno said:

Yes, read it carefully.

So tell me again why the first sentence in your initial post was not wrong or rephrase it so I can understand what you actually mean please.

[Moreno]

2 hours ago, studiot said:

So tell me again why the first sentence in your initial post was not wrong or rephrase it so I can understand what you actually mean please.

Sorry, in the my first sentence I've used a generalized expression "Schottky type of contact" for both Schottky junctions and ohmic contacts. Probably, I would have to use "metal-semiconductor junctions" instead.

[studiot]

1 hour ago, Moreno said:

Sorry, in the my first sentence I've used a generalized expression "Schottky type of contact" for both Schottky junctions and ohmic contacts. Probably, I would have to use "metal-semiconductor junctions" instead.

Just use the conventional terminology, like everybody else.

Then there is no confusion.

A Schottky junction is the same as a metal-semiconductor junction.
The emphasis is on the word junction the other words distinguish it from a semiconductor junction device.

The other alternative is called an ohmic contact and does not include the word junction.

 

Now that we have got that cleared up how about being more specific with your actual question that a link to an 11 page pdf?

(Glancing through the document suggests it is worth reading, )

 

[Moreno]

4 minutes ago, studiot said:

Just use the conventional terminology, like everybody else.

Then there is no confusion.

A Schottky junction is the same as a metal-semiconductor junction.
The emphasis is on the word junction the other words distinguish it from a semiconductor junction device.

The other alternative is called an ohmic contact and does not include the word junction.

 

Now that we have got that cleared up how about being more specific with your actual question that a link to an 11 page pdf?

(Glancing through the document suggests it is worth reading, )

 

Isn't an ohmic contact a variety of a metal-semiconductor junction? In the case when the later doesn't have rectifying properties? 

My question was: why contact of a higher work function metal and a lower work function P-type semiconductor is an ohmic junction? When we apply potential and make electrons flow from metal to semiconductor in the case above doesn't semiconductor suppose to case resistance to such flow? And also, if electrons start to flow from metal to semiconductor, doesn't they suppose to recombine with holes and make semiconductor depleted for any kind of carriers further increasing the resistance? How P-type semiconductor can conduct free electrons, those which belong to conduction band of the metals?

 

 

 

[Moreno]

Principally, similar question can be related to p-n junction.

Quote

 

Only majority carriers (electrons in n-type material or holes in p-type) can flow through a semiconductor for a macroscopic length. With this in mind, consider the flow of electrons across the junction. The forward bias causes a force on the electrons pushing them from the N side toward the P side. With forward bias, the depletion region is narrow enough that electrons can cross the junction and inject into the p-type material. However, they do not continue to flow through the p-type material indefinitely, because it is energetically favorable for them to recombine with holes. The average length an electron travels through the p-type material before recombining is called the diffusion length, and it is typically on the order of micrometers.^[1]

Although the electrons penetrate only a short distance into the p-type material, the electric current continues uninterrupted, because holes (the majority carriers) begin to flow in the opposite direction. The total current (the sum of the electron and hole currents) is constant in space, because any variation would cause charge buildup over time (this is Kirchhoff's current law). The flow of holes from the p-type region into the n-type region is exactly analogous to the flow of electrons from N to P (electrons and holes swap roles and the signs of all currents and voltages are reversed). https://en.wikipedia.org/wiki/P–n_junction

 

But if in the case of p-n junction there is flow of holes into n-type region (forward bias), how there could be flow of holes into metal in the case of metal-semiconductor ohmic contact? Monovalent metals typically conduct no holes...

 

[Endy0816]

Top is unfillled for monovalent. Easy route for electrons.

You need gaps forming and then multiple electrons changing positions in the valent band for holes.

[studiot]

Very quickly this morning,

Some things to realise about what is shown in common textbooks.

Textbooks tend to consider the 'equilibrium' contact and how it is achieved, usually using energy diagrams.

This is the position in figures 1 to 4 in your link.

But there will be zero current flowing in this situation, because there is no complete circuit established.

Your link is good because it has a figure 5 which is not an energy level diagram but a voltage / current plot whic shows a complete circuit as well as ohmic (5b) and Schottky action (5a).

Working out how the current is carried in a complete circuit will help you a lot. Especially as there is a big difference between P type and N type semiconductors.

 

I don't have time to draw any diagrams until later.

[Moreno]

14 hours ago, Endy0816 said:

Top is unfillled for monovalent. Easy route for electrons.

You need gaps forming and then multiple electrons changing positions in the valent band for holes.

Forming gaps between what and what?

Can you explain it more in detail? In some monovalent metals (for example Sodium) all valent electrons are located in conduction band. The valence band is completely empty. In order to conduct holes a material needs to have partially filled valence band. How can you inject holes in a material if its valence band is completely empty? 

Also, if forward bias action of a p-n junction or (possibly) metal-semiconductor ohmic contact is based on constant carrier recombination, how it comes that very little energy is wasted? Doesn't intensive carrier recombination suppose to consume lot of energy and furthermore lead to material overheating? (What suppose to increase resistance in metal at least.)

 

Edited March 19, 2019 by Moreno