Why does the diode behave like a short circuit?
Why does the diode behave like a short circuit?
(OP)
I have a diode where the mesa structure has layers as follows-
material 1(P+)
thin region (10nm) of material 2(P-) different badgap
material 1(N-)
material 1 (N+).
Overall it is a PIN structure. All materials are narrow bandgap, in mid IR region (~300meV).
When I measure I-V, I get a more-or-less straight line. The resistance is tens of ohms. The device behaves as if there is no P-N junction. I have earlier worked with a similar structure without the thin region and that gives good R0A values.
Do you have any idea why this might happen? I had some ideas but looks like those are not the right reasons according to further experimentation.
material 1(P+)
thin region (10nm) of material 2(P-) different badgap
material 1(N-)
material 1 (N+).
Overall it is a PIN structure. All materials are narrow bandgap, in mid IR region (~300meV).
When I measure I-V, I get a more-or-less straight line. The resistance is tens of ohms. The device behaves as if there is no P-N junction. I have earlier worked with a similar structure without the thin region and that gives good R0A values.
Do you have any idea why this might happen? I had some ideas but looks like those are not the right reasons according to further experimentation.





RE: Why does the diode behave like a short circuit?
TTFN
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RE: Why does the diode behave like a short circuit?
RE: Why does the diode behave like a short circuit?
TTFN
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RE: Why does the diode behave like a short circuit?
RE: Why does the diode behave like a short circuit?
1. You did not destroy it when testing.
2. The device is fabricated the same way that other working devices were fabricated. So, it does work.
Conclusion: Nothing wrong with anything. Is that what you are telling us? What do your colleagues say? Or are you doing this alone, in your basement?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Why does the diode behave like a short circuit?
TTFN
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RE: Why does the diode behave like a short circuit?
Here are a few other things -
1> The doping profiles were not right during the structure growth creating no P-N junction. (This is not the case. I have done a SIMS profiling and the dopants are present. There is no reason to believe that the dopants are not activated.)
2> There is something wrong at the device surface. Without proper passivation, low bandgap materials can be very leaky. However I think the resistance is too low even for an unpassivated diode.
3> The material has too many defects. I plan to do XRD/TEM to check that.
4> Is there something fundamentally wrong with the structure? Can the thin layer lead to too high tunneling or in some other way disrupt the P-N junction behaviour? An initial analysis suggests it is not the case but I am not sure.
RE: Why does the diode behave like a short circuit?
RE: Why does the diode behave like a short circuit?
What are the doping levels? Unless you have degenerate layers, you can't get tunneling. Even then, a standard IV test would reveal the negative resistance regime.
TTFN
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RE: Why does the diode behave like a short circuit?
5e16(10nm layer)
3e17
Note that these are low bandgap materials.
RE: Why does the diode behave like a short circuit?
Can you do a spreading resistance profile to determine the finished profiles?
TTFN
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RE: Why does the diode behave like a short circuit?
I would be interested to know if anyone has come across a diode (silicon or any material) which behaves like a short but is NOT burnt. Any other reason that might have rendered the diode behave like a short.
Thanks IRstuff and Skogsgurra for your replies. I appreciate your thinking through the problem.
RE: Why does the diode behave like a short circuit?
TTFN
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RE: Why does the diode behave like a short circuit?
That wasn't the point. Inactivated dopants result in intrinsic behavior. The SRA would tell you if your lightly doped regions are overrun, or if you have metal contamination.
TTFN
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RE: Why does the diode behave like a short circuit?
Thanks for clarifying the SRA point. So you are suggesting that the metal might have diffused into the junction.
RE: Why does the diode behave like a short circuit?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Why does the diode behave like a short circuit?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Why does the diode behave like a short circuit?
RE: Why does the diode behave like a short circuit?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Why does the diode behave like a short circuit?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Why does the diode behave like a short circuit?
Overalloying, or overcurrent, can cause the diffusion to reach far enough to snuff the junction.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Why does the diode behave like a short circuit?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Why does the diode behave like a short circuit?