Calculating Resistivity of Extrinsic Ge w/ Four Probe Method

[sukhbinder]

We have an experiment of the students to calculate the resistivity of an extrinsic (p or n) Germanium sample using Four Probe method at different temperatures (the sample is heated from room temperature and the voltage and current are measured for increasing temperature and then the same is done during the cooling if the sample).

In the aim of the experiment is mentioned to heat the Ge sample to maximum 200 C. I remember during my college days a teacher of ours mentioned that the Ge sample should not be heated above 80 C as above that the extrinsic Ge will become intrinsic.

I know that the max operating junction temp of a Ge device is 80 C and for a Si its about 150 C but i can't seem to relate to the extrinsic Ge converting to intrinsic Ge above 80 C (why did they mention the max temp. as 200 C in the aim)

Any one have any idea about this?

 

[BigJDubs]

The temperature limit of 80 C for a Germanium sample is a general guideline and not a strict rule. It is possible to heat the sample beyond this limit, however, the resistivity of the sample may be affected. Depending on the type of experiment and the accuracy of the results needed it may be safe to heat the sample up to 200 C.