# reverse biased diode variable resistance experiment

Discussion in 'Electronic Design' started by Jamie M, Dec 2, 2013.

1. ### Jamie MGuest

Hi,

This is related to the "poor mans superconductor wire" thread,
for testing an idea of anomalous resistance decrease in a diode.

If you reverse bias a diode, then electrons move closer to the
junction of the diode as the voltage pressure increases. I was
thinking maybe this biasing of the electric field will change the
electrical resistance on each side of the diode. Ie. if the actual
diode IC die is available to probe, reverse bias the diode, and then
put two probes on one side of the diode and measure the resistance
from two points on the anode-anode or cathode-cathode and see if the
resistance changes based on the level of reverse bias. Any ideas?

I was thinking about this in the case of topological insulators,
where with an infinite voltage breakdown diode, eventually it will
act as a topological insulator in this case and may then act as a
superconductor in this case.

cheers,
Jamie

2. ### Maynard A. Philbrook Jr.Guest

Yeah, they call it a zener diode!

3. ### Fred McKenzieGuest

Jamie-

The effect of changing a diode's reverse bias results in junction
capacitance changing. One Varicap data sheet I checked shows lowering
capacitance as Voltage increases. I believe the electrons move away
from the junction as reverse Voltage increases.

What you describe sounds like an inside-out field effect transistor. I
can imagine there might be some variation in resistance, but why do you
think it would be superconductive?

One problem is that you may not be able to probe such a small area. You
would need to design a device with molecular-sized electrodes. To use
the resistance, current must flow, and some of that current might be
"injected" into the junction. Now it is sounding like an SCR!

Fred

4. ### Frank MilesGuest

You may want to read some more about how PN junctions work. The depletion
region _widens_ with increased reverse bias potential.

5. ### Robert BaerGuest

* See Chapter 7, Transistors and Active Circuits by J. G. Linvill and J.
F. Gibbons, MgGraw Hill 1961, especially pp158-173.
* Perhaps you better read the whole book.

6. ### Robert BaerGuest

This variable resistance (of a zener diode) was used as a crude high
voltage shunt regulator for PMTs.
One manufacturer (Comprobe) of oil well logging sondes utilized
conventional silicon diodes as high voltage regulator devices. The
diodes had to be selected for appropriate reverse leakage
characteristics, a time consuming process resulting in a low yield of
usable devices. The leaky diode high voltage regulator was unreliable
and extremely temperature unstable, and its use was long ago discontinued.

7. ### Jamie MGuest

Hi,

I meant a variable resistance from one section of the anode to another
section of the anode, (or one section of the cathode to another section
of the cathode) - but not a variable resistance across the junction.

I should study more before I post though you are right (thanks!)

cheers,
Jamie

8. ### Jamie MGuest

Cool didn't know you can actually use a diode as a JFET (as long
as you have access to the die to put on another wire)

cheers,
Jamie

9. ### Jamie MGuest

Hi,

I was interested in a theoretical superconducting JFET, ie one that
doesn't quite fully shut off the current flow, but leaves a surface
flow of electrons like a topological insulator for zero resistance
flow.

cheers,
Jamie

10. ### Jamie MGuest

Hi,

In a JFET, if you turn it off, right before it turns off maybe there is
a nonlinear resistance spike when the resistance goes down right as the
electrons are only conducting on the very outer area. This would make
sense as the JFET turns off when the electrons are only conducting on
the outer surface of the silicon, so at that point the conduction case
is different than if the electrons were traveling within the silicon.

Also to keep the fine balance of electric field necessary for only
surface conduction, right before the JFET is turned off, maybe a light
could be shone onto the surface to allow surface conduction, even with
a fully turned off JFET.

cheers,
Jamie

11. ### Robert BaerGuest

Reading a bit of Linvill?

13. ### Robert BaerGuest

Yes; in a previous posting,i referred to a particular set of pages in
his book Transistors and Active Circuits - when responding to musings
regarding reversed biased diodes and negative resistance.

14. ### Jamie MGuest

Hi,

I unfortunately don't have the book, sounds interesting though. Might
take a trip to the library for that one.

cheers,
Jamie

15. ### Jamie MGuest

Hi,

"Pressure transforms a semiconductor into a new state of matter"
[topological insulator]

http://phys.org/news/2013-12-pressure-semiconductor-state.html

In this case they used extreme mechanical pressure, but I think
voltage pressure could do the same thing for certain materials or
metamaterials.

cheers,
Jamie