How does annealing improves the ohmic contact?

[madphdstudent]

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?

 

[ZapperZ]

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 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?

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

Zz.

 

[madphdstudent]

OK just made a typo.. Corrected.

Still question remains. What is the effect of temperature ?

 

[ZapperZ]

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.

 

[madphdstudent]

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 let's 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.

 

[Vagn]

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 let's 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.

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.

 

[Hongtu]

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 let's 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.

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.