Greetings.

I have been trying to fabricate a Hall bar on a SiGe/Ge heterostructure for transport measurements and so far my devices have failed to show ohmic behaviour at low temperatures. I have troubleshot several possible issues, from the cleaning process of native oxide before the ohmic metal deposition to the annealing of the ohmic contacts. Now, the last issue I have stumbled upon is the geometry of my devices. I have found the information in the picture attached to this message. I have deposited my ohmic metal all along the Hall bar arms, making it more like the top figure. I imagine this is a mistake as it seems to increase the error.

My question is, why is this important? Why the relative dimensions of the Hall bar arms are important and how they influence measurement? Also, why shouldn't the contacts be close to the main channel like in the top figure?

A colleague of mine has successfully fabricated a Hall bar and by checking his design, the difference with mine are a very large area for the ohmic contacts and the deposition of ohmic metals at the "tip" of the arm. This is why I am wondering how the position of the ohmic contacts affects the measurement.

Thank you very much.

Best regards,

Gabriel.