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Vigilatny Registered Member #17
Joined: Thu Feb 02 2006, 02:47PM
Location: NL
Posts: 158
Anyone know anything about this? Sounds like they modified a Schottky diode to work like a gunn diode. Or is it just a Gunn diode of exotic composition? A cursory google search seems to turn up mostly stuff about about amplifiers.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Sounds interesting. I did a bit of reading and sure enough, it seems that there's a device used for generating THz waves that's a cross between a Gunn diode and a Schottky diode, called a TUNNETT diode. I don't think this implies that we can get THz radiation from ordinary Schottky rectifiers though.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Funny this should come up, considering that I spent most of the summer working an a THz spectrometer I will admit that I was not involved in the design (that happened a long time ago), but I did get a decent look at how they worked.
They used a block of ErAs:GaAs to produce (and detect) the radiation. I cannot say how similar to a schottky diode it was in construction, but I do believe it was being used as a diode. They referred to it as a 'photoconductive switch' or 'photomixer' or just PCS
To actually get the THz out of it they focused ~50mw of laser radiation at 2 diferent wavelengths (one was at 780nm and the other at somewhere between 200ghz to 2thz above that) into the GaAs element and applied a bias of about 30v to it, and they (are supposed to) get ~5uw at .2-2THz out.
How it works is... You had the 2 diferent wavelengths being mixed together, and you get constructive/destructive interference (or something) So the output frequency is difference between the two wavelengths. (remember that 1nm = 500Mhz). This is then fed into the PCS, and as its name implies it opens/closes at the frequency of the light coming in. This puts a THz component on the 30v bias running through the switch. There is a spiral antenna plated on the GaAs substrate, which transmits the THz radiation.
I suppose it would be possible to modulate the signal by changing the bais voltage, or affecting the light coming into the sensor...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
A rather ancient - and probably mostly forgotten - way of generating reasonable power at very short wavelengths consisted of passing a high voltage arc through a suspension of metal particles in oil, each one of which then acts as a tiny quarter-wave resonator radiating microwaves.
I wonder if this technique from the earliest days of microwaves might be worth re-visiting with some of the nano-particles now available.
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Terahertz from a Schottky diode?
