# How does annealing improves the ohmic contact?

1. Apr 16, 2015

Suppose we have a p-type material and metal contacts deposited taking the work function of a metal and semiconductor into account. At room temperature (depending on the doping level) they might now show non-linear IV curve (non-ohmic behavior). How does annealing at higher temperature improves the ohmic contacts and eventually become ohmic? Is there a way to calculate at which temperature to expect the transition?

Last edited: Apr 16, 2015
2. Apr 16, 2015

### ZapperZ

Staff Emeritus
Er... linear IV curve means that it is OHMIC!

Zz.

3. Apr 16, 2015

OK just made a typo.. Corrected.

Still question remains. What is the effect of temperature ?

4. Apr 16, 2015

### ZapperZ

Staff Emeritus
This, I don't know, because it could easily depend on the type of contacts being used and the type of semiconductors. The only thing I can think of is that annealing burns away the oxide layer in between the metal and the semiconductor. Without knowing what kind of contact that was made and the material involved, this can only be a guess.

Zz.

5. Apr 16, 2015

Thanks for your reply zz. That definitely is true. Here materials does not matter here since I am asking the temperature dependence of the barrier potential right? Only numeric here would be work functions (work function of a metal> work function of the semiconductor) - meaning they should make it ohmic. But If that would help lets suppose that the contact metal is silver and semiconductor is p-type silicon. How does it become ohmic with temperature and how they remain ohmic is my question.

6. Apr 17, 2015

### Vagn

Anything that has been exposed to atmosphere will have adsorbed layers of adventitious carbon, water etc. on the surface which is typically insulating. By annealing after deposition you effectively remove some of this carbon (this is most obvious in an ultra-high vaccum.) The temperature is a function of the bond strength between the adsorbed species and the material.

7. Apr 21, 2015

### Hongtu

Some ohmic contacts do rely on formation of metal-semiconductor phases (e.g. formation of Ni-Ga-O phase in case of Ni/Au contact on p-GaN). So it's important to identify the material you are interested in.