We use ECOPIA Hall Effect measurement system (Model no. HMS-5300 + AMP55T magnet) in our lab. I am trying to determine the carrier concentration and mobility of PbS thin films. I have made electrodes at the four corners using Gold. I have measured I-V curves of the samples, the shape of the I-V curve is linear (an ohmic contact is formed between PbS and Gold). I did hall measurement of a sample at same condition for three times, it gave me positive hall coefficient for two times and negative hall coefficient for one time. The value is not in the same order and the polarity changes randomly. Even successive measurement runs on the same sample without changing anything at all, is showing completely different results. Why does it show positive and negative Hall Coefficient randomly in different for the same sample at the same temperature? What could possibly be causing this behavior and how can it be overcome?
Dear Ameni,
I would advice you to observe the hall signal with an oscilloscope. Your signal must be a DC signal if you have clear hall voltage polarity. I expect that you will find strong noise voltage superimposed on you dc signal which may much stronger than the DC Hall voltage. Also , if the sample is high ohmic it can pic up nearby alternating field . Please analyse your signal to get out the cause. I think your specimen is nearly intrinsic and high ohmic.
Best wishes
Dear Ameni,
I would advice you to observe the hall signal with an oscilloscope. Your signal must be a DC signal if you have clear hall voltage polarity. I expect that you will find strong noise voltage superimposed on you dc signal which may much stronger than the DC Hall voltage. Also , if the sample is high ohmic it can pic up nearby alternating field . Please analyse your signal to get out the cause. I think your specimen is nearly intrinsic and high ohmic.
Best wishes
Hi Ameni,
The post-processing for measurement #2 looks a bit weird. Could you please clarify it ?
The AC and BD Hall voltages are of same polarity for all the 3 measurements, so the Hall coefficient should be consistent for your sample. But the average Hall is negative for measurement #2. It might be cool to just consider the AC and BD raw measured voltages and then double-check the post-processing.
Every equipment has its detection limits, maybe you are at it. Back track to the raw numbers being measured and see if your hardware is at its limits.
I even once had the bizarre issue that I got the craziest Hall coefficients because my electromagnet was water cooled and so my sample cooled a little when it was close to the magnet, and the temperature dependence of its conductivity was greater than the effect of the magnetic field.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructures
- Thin Films