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Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
I just found a paper about dual gate mosfets that includes a brief historical summary about the MOSFET. It is being said that the first patent to mention a mosfet-like structure war handed in by Julius Edgar Lilienfeld back in 1925. This gentleman did some experiments with Cu-Cu2O Schottky junctions. Hole mobility is half that of p-Si, hole density is about 10^15 cm²/Vs but it can be increased by 2 orders of magnitude by adding Si as dopant. Since the maximum current density is quite low and the majority carrier mobility is a pain, no one (to my knowledge) has bothered experimenting with FET structures of this material.
Ohmic contacts can be formed through lead or gold metallization, copper forms Schottky barriers. I hope I got the lattice orientation of the bulk right, since copper(I)oxide has good properties when grown in a (111) layer and crystalizes in a cubic system. See for nice illustrations. Please correct me if I got it wrong.
When the oxide semiconductor layer is made thin enough, the barrier could be made to significantly limit the remaining channel width. Positive gate voltages will then pinch off the channel. Since copper oxide is quite forgiving in regard to current spikes this might be the first jFET structure that is forgiving to electrostatic discharges
Now tell me, might this device by any chance work as a jFET?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Assuming Cu-Cu2O does indeed form schottky junctions then it looks basically like a textbook JFET. In order to ensure that current does not flow from the channel to the bulk Cu(111) layer I think you'll need to bias the bulk at the drain voltage to ensure there is a depletion region, if the Cu2O is p-type. Conversely with an n-type channel you would bias the channel at the source voltage (presumably "ground") to ensure the channel-bulk junction is always reverse biased.
Edit: See for some homebrew Cu2O detectors, and for some research.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
Thank you for the links, they help very much. Cu2O and CuO both seem to be intrinsic p-type semiconductors due to copper vacancies but at least Cu2O can be made into an n-type material by changing the pH during electrochemical deposition. active structures such as the jFET suggested above might be within reach of any amateur experimenter, even if the gate needs to be created by continued deposition with a different pH level after masking out windows, thus creating a p-n junction.
Edit: just found this brief summary of "buried physics" formulas to guess some specs of the proposed device:
And here are some scarce papers I found on Cu2O TFTs: epitaxial (110) Cu2O films on (110) MgO substrate, field effect mobility ∼0.04 cm²(Vs)^−1 Cu2O films on (110) MgO substrate ∼ 0.26 cm² (Vs)^−1 Copper oxide (CuxO) thin films on SiO2/Si substrate, Hafnium oxynitride dielectric used for MOSFET, on-off current ratio of 3 x 10^6, a saturation mobility - 4.3 cm²/ V s
as MOSFET structures are possible, MESFET structures should be, too. I wonder how hard it will be to construct a device with low-tech methods.
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Cu2O p-channel jFET (MESFET) or: what Lilienfeld did not manage to build
