7/02/2007

gadget fixation: OLET, part two

First, I have to say that I'm actually kind of amazed that people read device posts now. Effectively, this means that the CBC authors can now write about whatever we want and you will read it.[1] Part one of my little foray into OLETs can be found here. This is part two. I'll admit that I'm partially doing this because these are nifty little devices and I wouldn't mind a side project on them at some point (HINT HINT to someone whose IP shows up here occasionally).

Last time we left off with the invention of the first LET by some apparently important guys over at Excimer's school.[2] Now I bring you the happy fun carbon version of those devices. In case you're curious, this is the first thing published on them.[3] (This was easy to look up because it is stated in their first sentence. Why can't everything be so simple?) The group who did this used tetracene, which should be familiar to all the organikers here if they know their aromatics (or really anyone else who reads this blog on a regular basis).[4] Back to the subject at hand, the device architecture is deceptively simple. They use n-doped silicon for the gate electrode, a thermally grown oxide layer as the gate dielectric, and gold for the source and drain electrodes. The source and drain are interdigitated (which I appreciate because it gave me the opportunity to excercise a far-underused word), and the tetracene is applied top-contact-style. I won't go into surface treatments or show a picture because that's what the original paper is for.



Quick review of the inner workings of an OLED: Electrons and holes are injected and recombine in an emissive material, resulting in light. The OLET works in a similar manner. This means that some electron injection is taking place. Naturally, the electron mobility in tetracene (as for most organic semiconductors) is pretty low--it's p-type, duh, so we really don't expect much electron injection at all. I should probably also mention that the guys who made this observed all the light emission from around the drain electrode. And that the tetracene was deposited by thermal evaporation.




As it turned out, the light emission they saw was a result of some weird contact issues with the source and drain electrodes. Normally, people shoot for a device as shown in the top of the picture, in order to assure nice contact with the electrodes. As it turns out, that's not what the authors of the paper got, but hey! It did something cool anyway. I'm not sure whether or not that might have been serendipity at work--it appears to have been submitted (though not published) before the InGaP/GaAs LET paper I mentioned in part one. Curious, hmm?

I was planning to do only two posts on this subject, but it's been kinda fun writing these, so I may do another.[5] Admittedly, all I've covered thus far is old news by a few years, but it's still new ground for me and probably quite a few of the synthetikers, so some background seemed to be in order. Right?

[1] MWAHAHA!!!
[2] "The inventor of the LED" and "the creator of the world's fastest transistor" are two phrases that kept coming up when I was Googlestalking them.
[3] I'll admit that I'm definitely not in the habit of reading any physics journals on a regular basis, but searching for information to write this post (and OLETs part one) kinda makes me want to get on that. (What? Physics is useful?)
[4] Because we TOTALLY have an acene fetish. Can you blame us? They're so pretty...
[5] This has nothing to do with the mysterious connection between writer's block and lit posts. Nothing at all...

5 comments:

Uncle Al said...

It's unfundable unless it contains nanotechnology or stores hydrogen. Being a diagnostic device for orphan diseases would help.

Slap some HIV virus on there, flip the switch. If HIV viability at one electrode statistically decreases... a potential therapeutic paradigm for HIV treatment in the manner of extracorporeal renal dialysis. More studies are needed.

mevans said...

I guess we could say that kinky contact leads to little photonic babies...?

There does seem like there's a lot to be done...haven't found one yet that emits blue light!

milkshake said...

You mentioned that higher acenes are pretty unstable. I wonder if some oxidized/oligomeric product could have formed in the gaps...

Sometimes things take a little schmutz to work properly. There was a story about a physiology lab many yeras ago that was working on temporary preservation of organs for transplant. They had particular problem with keeping hearts alive, unlike kidney that could be kept on ice for hours, heart without blood becomes damaged in minutes. One student had particularly good results, his hearts were most long-lived but nobody could reproduce his work. Then it turned out that he was rather sloppy, making his solutions from the tap water instead of DI. It was the Ca, Mg traces from tap water what was needed to keep the hearts happy.

Ψ*Ψ said...

AFAIK--and I don't know everything so don't quote me on this--the stability issue with acenes is more of a concern when they're in solution. That depends on the molecule, though...tetracene and pentacene I think are OK in the solid state, but I have seen some compounds turn into the corresponding quinones after just sitting around on the bench for a while. As far as the cause of the gaps, well, that would be the funny-shaped electrodes. Thermal evaporation onto that surface would leave a gap with no tetracene in the "shadow" of the source and drain.
The heart story is pretty interesting. Thanks for bringing that up.

Ψ*Ψ said...

*crickets chirping*
Um, yeah, I guess this means you guys really DO hate device posts.