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...