UIUC Researchers Create Light Emitting Transistor

thesilverbail writes "Researchers at the University of Illinois have demonstrated light emission from the base layer of a Bipolar Transistor. This discovery could be the beginning of an era in which photons are directed around a chip in much the same fashion as electrons have been maneuvered on conventional chips. It's reminiscent of the exciting days of the Miracle month November, 1947, when the transistor was first invented."

Comments

This doesn't seem to mean much

[Tau Zero]

First, there's no real magic here; the news release says that the transistor is "made from indium gallium phosphide and gallium arsenide."

What this means is that someone has taken the same materials which emit light as part of a single-junction device (a diode) and have also made them do so as part of a bi-junction device. While this looks like it might be a good way to integrate light emission with the control circuitry, it's not going to do anything to make them easier to integrate into large devices (silicon works for this because its oxide, SiO2, is a pretty good insulator while gallium doesn't do anything so convenient).

I will admit that it's clever, and someone may find some unobvious way of turning it into a useful device (massively parallel optical interconnects?), but there's just no way that this is going to be slapped onto the next Intel or AMD die. It especially will not replace aluminum or copper interconnects between parts of one processor.

This isn't what you think

[Cyclone66]

It's an extension of the idea of the Light emitting Diode but it doesn't mean we'll have optical computers any time soon. The transistor still runs on current, it only outputs light! That means it can not drive another LET which means fully optical based devices aren't possible.

What this DOES mean however, is smaller devices in the realm of electronic/optical interaction. The basic functionality of this transistor is similar to a small combination of transistors and diodes except that this does it in one device. The device is rather large but it'll probably shrink rather quickly as it's still in the early stages of development.

Re:This isn't what you think

[grayrest]

Actually, it outputs both current and light. The light just happens to be a byproduct of the electron-hole recombination in the material. I do believe that the two outputs will be either the same or opposite depending on transistor type (pnp or npn) so you really don't get anything out of the transistor that you weren't getting already, you just get it in a different format. I'm sure, however, that someone more creative than myself will find some cool use for this.

You're extremely unlikely to see this type of technology in a microprocessor, at least in it's current BJT form. Most if not all microprocessors use MOS-type transistors because they're much easier to fabricate. BJTs are usually used in electronic amplifiers, though either can be used in either scenario depending on how the circuit is set up.

Re:This isn't what you think

[jralls]

The main reason that FETs are used instead of BJTs in logic devices is that FETs are voltage devices while BJTs are current devices. Logic is much easer to implement with voltage. Amplification, on the other hand, works better with current devices. Hence the BiCMOS processes which are common in the mixed-signal world.

As for these light-emitting BJTs, unless the light is emitted instead of heat from the resistance losses (which I'd think unlikely), the gain and efficiency of the transistor will be reduced by the light emission.

That's nothing

[TheOnlyCoolTim]

This one time I made some smoke emitting transistors.

Tim

Nothing to get excited about

[JGski]

Since this was done on GaAs/InP, it pretty much assures that the massive adoption date is anywhere from Today+20years to Today+infinity. In case you hadn't heard, GaAs, and III-V in general, has been the "next big thing" in semductors for nearly 30 years now. It's pretty much a niche technology only used when Si absolutely can't do the job at any price because the price to do III-V is usually so high in capital and tech issues that Si, even when price inflated 1-2 orders of magnitude, is *still* overall cheaper.

Things that would get my attention:

implemented in SiGe instead of III-V materials

bidirectional transduction in O->E not just O->E at usable efficiencies

demonstration of integration into "conventional" manufacturing processes

Otherwise, it's an interesting academic exercise that might lead to the above points, which is "A Good Thing".

Big deal

[ScottForbes]

I invented a light-emitting resistor in a UIUC circuit design course over ten years ago. It only worked once, though, and it burned my fingers.

Where this may be useful...

[hobit]

The idea that this is somehow enabling optical computing is incorrect as these things can't take light as input. One could use a photodetector of course, but it doesn't seem like a big deal, one could use LEDs to do this today...

Debugging hardware could become simpler however. You could "see" (or have a computer watch) exactly what each transistor is doing. This could greatly enhance the ability to test real chips. Of course the transistors are usually buried under the metal layers, so I guess it depends on how bright the transistors are or if the designers are willing to leave (lots) of gaps in the metal layer for at least the "important" transistors.

Mark