In the case of semiconductor thin-films deposited on insulating substrates (e.g. glass), establishing vertical Schottky - Ohmic contact is not possible. Here, if one puts co-planar/lateral Schottky and ohmic contacts (having same contact area using same shadow mask) on the surface of the film, will it be foolproof to calculate the carrier concentration of the material by capacitance-voltage (C-V) profilings? If so, what will be the 'A' (area)?
Muhammad Hamza El-Saba
Dear Professor,
The layout is attached for your convenience.
Thanks and Regards,
I guess you need the area to calculate the capacitance. So the problem is to find the capacitance of a capacitor with this geometry.
Vesselin Donchev
What if one establishes Schottky contact with a defined area (using shadow mask at the time of metalization) like it was shown in the JPEG file attached herewith?
Yes, you can find the c-v with this configuration. Many commercial devices does this. Usually they make interdigitated Schottky and ohmic electrodes laterally to make planar Schottky diodes.
Depending the thickness of the SC layer compared to the size of your pads, you may encounter the TLM effect. I would suggest to vary the dimensions of your Shottky so that you can actually calculate your active area of the Shottky. Good luck!
In this geometry, the major problem would be the violation of depletion width approximation with a large error in the area calculations. It is not recommended geometry for estimating the absolute values of charge carrier density.
Vijay Kumar Dixit
Here, 'A' is the area of the depletion width extended in the semiconductor region and it is assumed that it (area of depletion width) is equal to the area of the Schottky contact. Now, the question is: whether it is vertical (top-down) or planar/lateral if the Schottky contact has a definite area, does it not come under the purview of the same theoretical (depletion width) approximation?
If below the contact there is no semiconductor thin film (i.e. the contact touches the insulator) the situation would be easier. In that case A= D*W (D=thickness of the film and W=width of the contact)
Read carefully any text book for the parallel plate capacitor geometry configuration along with depletion width approximation for the geometry shown in above figure. One can get clear idea why under charge anisotropic distribution (leakage) condition extracting charge carrier density is not appropriate.
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