Dear Neharana Rana

Dear colleagues ,

Allow me to share in your discussion.

YOU have deposited ZnO over ITO and then aluminum to produce an ohmic contact on the ZO. It is known that both ITO and ZO are intrinsically high concentration n-type. Therefore i would propose to measure the static IV characteristics of such structure to see how far it is conducting. The second notice is that to measure the electrical performance of ZO only the bottom electrode must be good conducting like aluminium and not semiconducting as ITO. Now, you measure the combined characteristics of the two semicoducting oxides.Since you contact the ITO from the side you have a complicated network of parallel connected capacitor s and resistors. You do not have a parallel plate capacitor as you assume. You will have such a parallel plate capacitor in case you changed the bottom ITO with AL as i said before. After that you have to measure the structure at relatively high frequency to lower its capacitive reactance in parallel with the conductance of ZO.

So my advise is to make the bottom electrode as the top electrode from AL. This may solve the problem ISA.

please inform us.

Thank you

Yes, you are right. Make one electrode on thin-film of the material and ITO itself will work as another electrode.

Remember to use a proper metal for the top electrode. Its work function should be similar to the deposited material if you want to have an ohmic contact. It may not be crucial if you want only to measure the dielectric constant of the material, but may be critical for any other electrical measurements.

Thanks for replying Sir,

Actually I have deposited ZnO on ITO/Glass and for contact I have used Al metal which is ohmic with ZnO, but the problem is that the order of dielectric constant 1000000 which i am getting is very large.

This is odd indeed, as one would expect it to be in order of 3...5. What method are you applying for the measurement?

Have you read this paper - http://iopscience.iop.org/0508-3443/9/11/308/pdf/0508-3443_9_11_308.pdf

Thanks for your guidance sir.

Neharana, if you are measuring dielectric through ac studies and extrinsic effects like work function (as discussed by NikodemCzechowski) and the varistor nature of the ZnO need to be properly addressed. The role of defects at surface some time brings colossal changes in the dielectric values. You need to check the tandelta values to understand this issue. If you think nothing is wrong with your contacts, use alternate options for contacts. Also its important to look at dielectric values at high frequencies.

Respected Sir,

I have deposited ZnO film by using sol gel spin coating on ITO/glass substrate(film was annealed at 600 degree Celsius) then contact of Al metal was deposited by thermal evaporation.

By using 6520A impedance analyzer , i have done capacitance vs frequency measurements, from that by using parallel plate capacitor formula I have calculated dielectric constant, that is what I have done.

Ur colossal value of dielectric should be at low frequencies which is from surface/contact region. Its better to opt different options like Gold and In-Ga alloy for better understanding. In pure ZnO you can expect dielectric values like 1000 at low frequencies but at high frequency it must be in decades.

Are you doing C-V measurements of ZnO over ITO? You should try to evaporate gold as top contact with has a high work function. It also have the advanage that will not diffuse into the ZnO substrate. You can end up doping your ZnO with Aluminum.

Dear Neharana Rana

Dear colleagues ,

Allow me to share in your discussion.

YOU have deposited ZnO over ITO and then aluminum to produce an ohmic contact on the ZO. It is known that both ITO and ZO are intrinsically high concentration n-type. Therefore i would propose to measure the static IV characteristics of such structure to see how far it is conducting. The second notice is that to measure the electrical performance of ZO only the bottom electrode must be good conducting like aluminium and not semiconducting as ITO. Now, you measure the combined characteristics of the two semicoducting oxides.Since you contact the ITO from the side you have a complicated network of parallel connected capacitor s and resistors. You do not have a parallel plate capacitor as you assume. You will have such a parallel plate capacitor in case you changed the bottom ITO with AL as i said before. After that you have to measure the structure at relatively high frequency to lower its capacitive reactance in parallel with the conductance of ZO.

So my advise is to make the bottom electrode as the top electrode from AL. This may solve the problem ISA.

please inform us.

Thank you

Hi

I just want to add one more point here. From DC biasing with AC , you can monitor contact effects. Plot of DC bias voltage with inverse of capacitance is important for further investigation of contact.

Try different contacts and then analyze which one is better in your case(Better should be that one whose work function is comparable to ZnO). and large value at lower frequency may be due to electrode or interface effect.

hope this will be useful for you.

Thanks

Thank you all for your advise and discussion keeping all these points in mind i will try to implement these for my experiment set up.

To

Dr Kamran

As you replied that by using inverse capacitance versus voltage measurements can be used to to study the contact effect, as much I know this CV study mostly used to calculate doping concentration and barrier height. So you want to say the better contact will be the one which has lower barrier height for Dielectric measurements,

# Am I correct Sir?

# Also in literature metal like Al shows ohmic type IV characteristic with ZnO film and Ag shows schottky type type characteristic,

So for Dielectric study is it better to use Al then Ag as it has ohmic IV characteristic?