If you can measure all needed potentials in 4-point contacts/square sample geometry, you can extract both Hall carriers concentration and sheet resistance by van der Paw technique (see e.g. https://en.wikipedia.org/wiki/Van_der_Pauw_method). Although the current value should be in linear (ohmic) region to avoid interfering effects as hot carrier injection and channel pinchoff.

For sheet resistance, 4-point probe is a very user-friendly tool.

Dear Shreya Roy,

could you show, please, your  "I -v Curve" ?   (Your  i -V  is using 2 or 4 contacts ?)

Also, could you show, please, a scheme of your contacts on the sample ?

@ I.S. Vasil I have attached data which is 4 point contact van der paw geometry data.

I-V curve is not a completely straight line.  Still, can I consider the data as good?

@ Loannis samras Please see the attached file sir. It is 4 contacts. It is 15 nm WS2 thin film on glass substrate and 4 indium contact at the corner

Dear Shreya Roy,

what is the Voltage Compliance (VC= ?) of your i-source ?  

Is there any Voltage Compliance pre-set (of about : VC=10V  ?) either by software or by hardware  ?

Also, could you show, please, a schematic of your contacts (on the sample) ? 

5mV to 50mV is the instrument range of operations

We can see (in: 02 27 17 anled.docx), by focusing on your " i -V" plot,  that there is an obvious Voltage limitation (10V).

This V-limitation  (10000mV) might come from a Voltage Compliance pre-set, in your current source, either by software or by hardware (?).

Dear Shreya Roy,

It looks like you amplifier was saturated at above +/-0.3nA (amplification is too high) or maximum voltage is limited by software or hardware.

First of all, you have to check what is the maximum voltage limit was selected (Voltage Compliance pre-set, mentioned by Ioannis Samaras) for this measurement.

I'm afraid that you cannot extract resistance from only Hall effect measurement. Usually, you have to use Van der Pauw or 4-point probe measurement to get the sheet resistance.

Very often the specific resistance is required to calculate Hall mobility

(http://www.tek.com/sites/tek.com/files/media/document/resources/LV_LR_e-hnbook_91113.pdf see p.14)

In this case, you have to perform multiple van der Pauw and Hall measurements for offset cancellation. If your system is configured to collect this data automatically, you will be probably able to extract it from a datafile, if available. Otherwise, you have to perform some extra measurements according to van der Pauw routine.

Best regards

Yevhen

At Yevhen.

First of all thank you very much for explaining.

Few Informations that you have asked, I  am mentioning below

According to company , that instrumental applied current should be such that resulting voltage should be in the range of 5milivolt to 50milivolt. They give instruction that we should not try very small current. But our film have highly resistive so we need to use low current.

I am using van der pauw rectangular sample geometry with contact at four corner. can you please provie me any suggestion what geometry shall I use for my 20nm thick films.

Thank you so much for helping me

Dear Shreya Roy,

your rectangular sample geometry (with 4-contacts at four corners) is good for the Van Der Pauw (VdP method for) resistivity.

1) What is the size of your film ?

2) What is the error value (E%, in VdP resistivity) ?

Dear Shreya Roy,

as I can see from attachment you have HMS-5000 Ecopia system for Van-der-Pauw measurement. If everything is fine it should be able to provide you reliable data for both Hall and resistivity measurement.

But I-V curve shows that something is wrong.

If you calculate resistance between D and A points (DA resistance) it gives you about (6V/0.2nA) 30GOhm value. You mentioned what film is 20nm thick.

Can you check if it's continuous layer?

The SEM or AFM image can give you an answer on this question.

Van-der-Pauw technique is suitable for uniform and continuous sample only.

If film thickness becomes comparable with the defects size, surface roughness, dust particles etc on your substrate it probably becomes not continuous anymore.

If sample looks like a lot of islands which are interconnected somehow it's not uniform sample anymore. Due to percolation mechanism, it can be still conductive but current lines distribution can be significantly disturbed in such a case.

Best regards

Yevhen

Dear Shreya Roy,

you can try, also, to use a much smaller size (a sub-area[1]) of your film in order to reduce the intermediate (VdP) values of the R1 (or R12,34[2]) and R2 resistances used for the calculation of the Van Der Pauw resistivity method. It might help you to overcome a possible technical limitation due to your current source (Voltage Compliance), by using a smaller size (area) for the resistivity measurement.

1.  Higher (nominal, calculation) errors in a sub-area, but it might help you in practice :  Measurement of contact placement errors in the van der Pauw technique   http://aip.scitation.org/doi/pdf/10.1063/1.1140423

2.  https://en.wikipedia.org/wiki/Van_der_Pauw_method