Probe stations are typically characterized using known loads. If you use a short, an open, and a known resistance, you should have a pretty good idea if its OK. If you had access to a known-good diode or a transistor you could compare curves.

Thank you Doug!

As you are aware,  the diode or transistor cannot be placed on the chuck like a wafer as they would already have contact wires soldered to them.

Could such a diode or transistor be used to  accurately characterize the effect of the chuck, which forms the bottom contact ? 

For high frequency probe stations, they usually offer standards. I would check with the manufacturer for suggestions. Do you have the manual? There are places that sell devices as die, although handling can be problematic if you don't have a lab to handle such things. An example vendor is http://www.semidice.com/.

If the chuck is a big piece of metal, then the issue would probably be your backside wafer contact. If you don't do anything special, then you may get a schottky on the back which would be bad. We used Indium on GaAs for homemade ohmic contacts.

I am actually building it DIY and hence no manuals.  I don't have the budget for even a  portable station and hence the DIY.

The  chuck is made of tinned  copper plate. I was worried about the wafer back contact  too and that is what I would like to characterize. Were the In on GaAs contacts on the chuck or on the wafer?

Here are some random papers:

http://materion.com/~/media/Files/PDFs/Advanced%20Materials%20Group/ME/Challenge%20of%20Applying%20Ohmic%20Contacts

https://crn2.3it.usherbrooke.ca/guide_sb/procedes/contacts/ohmic-III-V_Baca.pdf

This would have been in the 1980s. I probably just pressed some In wire on the surface, but we probably did thermal evaporation as well. We also did InAu but that makes a hard alloy which is difficult to wirebond to.