I wanna measure the mobility of semiconductors with Hall effect but I don't know which contact is properly work. I measured the hall effect of conductors such as Au and Ag without problem but Is there any special principle in semiconductors? what is the geometry of the contacts?
The geometry of the contacts is the SAME. An ohmicity check of the (your particular) electrical contacts in (your particular) semiconductors, is always an additional, standard, issue.
A lot of metals create Schottky-barriers. Therefore it is mandatory to characteristic of the metal-semicondoctor contact. A linear relationship between current and voltage must be observed.
The contacts must be pointshaped and located near the edge of the sample. Otherwise a correction factor is to calculate - but this is not specific for semiconductors. It has generally to taken into account for precise measurements.
Well you have to find out what material will good ohmic contact. It will depend on the semiconductor u are trying to measure. Furthermore, just depositing metal contacts is not sufficient. One has to do RTA(Rapid thermal annealing) in a specific gas to reduce the contact resistance. Contact Resistance can be measured using transmission line method.
Remember that u are going to measure voltage differences in electrical measurements of semiconductors. As it is, the Hall voltage signal is much lower than the magnetoresistance, so one needs metals that have good ohmic contacts + RTA to reduce contact resistance. Contacts that have low contact resistance will have less voltage drop, so hopefully the voltage u are measure is close to the true hall voltage
Getting an ohmic contact could be easier for elemental semiconductors. But for compound semiconductors getting "true ohmic contact" is a serious issue. It generally depends on several factors including, the doping type, the effective work function of semiconductor and that of the metal, interfacial chemistry etc.
The best way to check ohmic nature is, deposit a metal contact (having a greater work function) on your sample and see its I-V characteristics.
Thank you very much. Could every one recommend an article about compound semiconductors and their contacts?
What is the material? What is its reported work function?
I believe it is not easy to predict the surface and interface properties of a compound semiconductor. It depends on several factors.
Dear Vali
I agree with you. My surface is containing ZnO nanoparticles. The problem is when I use different contacts such as Ag or Au in the corner of my square sample I get different mobilities. I don't know which of them is correct?
Dear Arezou Zarei, could you, please, illustrate more your sample[1] ?
1. your note (above): ... My surface is containing ZnO nanoparticles.
Dear Samaras
My sample is ZnO nanoparticles. As you know my layer is a semiconductor but I measured its resistivity with 2 probes of multi-meter. It was about 600 Mega-ohms. So I couldn't determine its Hall coefficient in room temperature. The work function of my layer is about 5.7 eV. I obtained its mobility at about 500K but the problem is: When I use different contacts, I obtain different mobilities!!!! What is the reason?
The mobility value with the Au-contacts is the best[1] measurement for an homogenous ceramic sample of ZnO nanoparticles, without any binder.
What is the mobility value with the Au-contacts ?
1. The Ag-contacts (in Oxides, near 500K) should be an issue, due to Ag-O formation.
Check if the contacts are truly ohmic before and after the Hall measurements.
The mobility is about 93 cm2/V.s. I checked the ohmic contacts before. The trends were linear in I-V figures.
For the determination of mobility of carriers, the Hall factor correction is required. However, this is often neglected due to lack of information about the Hall factor. Hope this clarifies your doubt.
- Badges
- Science topic
- Similar topics
- Biological Science
- Histology
- Sectioning