how to calculate the carrier concentration for semiconductor (bulk, powder) if the resistance is very high like Mega ohm?
I think Hall measurement and seaback coefficient measurement wont work in this case as the resistance is very high!!!
Dear Rajagopalan,
Hall measurements are difficult, if the mobility µ is µ < 1 Vs/cm². The resistance itself is not the problem. Important is the resistivity or better conductivity.
If the high resistance is due to a low carrier concentration than you could get problems for n,p < 1E14 cm-3. But then you can say, that your material is almost insulating.
The technical problem is the noise level. Here, the resistance indeed determines the thermal noise (kT-thermal energy, R "your" resistance, Df bandwidth):
Ueff = SQRT(4kT*R*Df)
Using an AC-method (low frequency-quasi DC and high selectivity - Df) you can reduce your noise but it is a more complex work.
With Regard
R. Mitdank
I must correct the upper unit for mobility. The unit is cm2/Vs.
I ask to excuse this error.
R. Mitdank
The Hall effect is used directly to measure the free carrier concentration in the material. This may be different from the existing grain bulk concentration because of the impedance of the grain boundaries in the noncrystalline materials.
The Hall voltage is inversely proportional to the free carrier concentration and so the generated hall voltage increases by decreasing the carrier concentration for the same current passing in the hall specimen.
see the paper in the link: Method Measuring the semiconductor parameters
The other way to measure the carrier concentration is to measure the conductivity sigma and the mobility mu and then use the relation between them:
sigma= q mu n with q the electronic charge and n is the mobile charge concentration.
In case of grains the grain boundary may dominates the resistance of the material.
In this case the resistance can be expressed in the form:
Rt = Rgb+Rb with Rgb is the grain boundary resistance and Rb is the grain bulk.
We since long time, studied the effect of grain boundaries on the resistance of the materials. Please follow the paper: Article A. Elemawy, A. Zekry, M. El-Koosy and H.F. Ragai, “Propertie...
Best wishes
@Rajagopalan Pandey,
You are right, for samples with high resistivity it is difficult to make ohmic contact. Contact resistance should be very low otherwise you will get a rectifying contact. You can try CV measurement to find out carrier concentrations.
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