Can you tell me what is the composition of your thin film?

the composition of my film is GaN.

Current value that you have suggested is correct it will vary between 1 mA to 1 microA. Mobility and charge carriers can also vary with the film thickness.

It sounds a bit that your are heating your film with the applied current. Does the sheet resistance change with the current? Did you check your contacts if they are omic? On GaN most metals will make a schottky contact. Use IV-curves made of several point puls and minus current to check for an omic behaviour in all six measurement arrangements.

The current should be between 1 mA to 1 microA.because mobility and charge carriers may vary with the thichness of the film.

We have used the input current of 1nA, but it was in case of high resistive semi-conductive films from Cu-As-Se-I system. Please see the attached files: The software window from which you may use some data and the paper with the obtained results and sample details.

Here is the paper.

I agree with Hans-Fridtjof Pernau that contacts might be your primary problem. On the other hand the purity of your film could influence the measurements, too.

I think you may be have a look on ASTM Standard F76 -2013 for measuring hall effect on thin film .

Generally current depends on the resistivity of the sample. In the case of sample having resistivity 1 milli ohm-m plus range can apply current ranging from 1mA to 20 mA

please check your measurement setup for interference parameters which greatly affect the resistivity and hall effect Determination , specially for high resistive films.

Generally you pay attention to the interference sources in your set up such as

1- photoconductive and photovoltaic

2- minority carrier injection

3- Temperature

4- high frequency generators

5- surface leakage of sample

6- the possible leakage paths in your setup such as switches ,cables,connectors,and the shunt paths around the film itself