Let there be light...emitting diodes

Wednesday, 05 October, 2005

Russell Dupuis talks about the development and future of this revolutionary technology in conversation with Jane Sanders.

How might the use of LEDs be expanded in coming years?

Right now, people see LEDs as having specialised applications, such as in the side and tail-lights of 18-wheeler trucks and buses and as tail-lights in high-end cars.

LEDs are so reliable. They don't have to be replaced often, if ever.

LEDs will be used in the headlights of the Audi A8 in 2006, and other car manufacturers will follow.

In offices, LEDs will eventually replace incandescent lights because the old technology is so inefficient. So much energy is wasted because incandescent lights put out heat. The calculations show we could cut the need for 33 nuclear power plants if LEDs replaced traditional lighting.

Edison's bulb is a wonderful thing, but it's very wasteful.

With all due respect to Mr Edison, we're encroaching on his space. At some point, all incandescent bulbs will be in museums.

There are good physical reasons that LEDs are the ultimate way to create light from electricity. In principle, they are 100% efficient internally.

You have to argue with Mother Nature about how to get the light out of the crystal and into free space, so you never really get 100% out.

But there's no other thing produced with an internal efficiency of 100% that can be used so effectively in compact form. There are competing technologies - primarily diodes made from organic polymers.

LEDs will become the dominant form of lighting in high-end buildings within the next 10 years because designers see energy use as part of the total picture.

LEDs will eventually be used in all offices and then in homes. Incandescent and fluorescent lamps are a form factor for these products. LEDs have a different form factor. But for a while, we're stuck with these bulb-like things.

People are not familiar with LED-designed things that function the same but are different devices to light the room.

If Thomas Edison was alive today, what do you believe he would think about the advances you and your colleagues have made in LED technology?

I can't image that Tom would be unhappy because he was such an inventive genius. But he was also very competitive, so he might be a little angry, though I think he would appreciate it all.

What were the major technological challenges in the development of LEDs that you and your colleagues conquered during the past 40 years?

Light-emitting diodes (LEDs) are devices largely invented in the 1960s. The first visible LEDs were made in 1962.

A process he developed could grow materials with multiple elemental components.

Semiconductor electronic circuits are generally composed of elemental materials like silicon or binary materials like gallium arsenide.

The emission from any diode made from these materials - by force of nature's plan - is not visible to the human eye. It's in the infrared spectrum.

Since he created the first visible LEDs, the term has come to refer to visible light-emitting devices of gallium, arsenic and phosphorus origin.

In the 1960s, materials like alloys - three-element compounds - were thought to likely be unusable because they are crystalographi-cally and chemically random.

They are not ordered materials like silicon or diamond or gallium arsenide. But Holonyak pushed the edge into unknown territory and added his own special wrinkles to the process of creating LEDs.

Holonyak's creation of visible LEDs is now called the 'Alloy Road' in semiconductor technology.

Today, billions of LEDs are made each month around the world, and those are all made from alloys. The alloys today are more sophisticated than the original ones.

They're grown with a different, more complicated process - called metal-organic chemical vapour deposition or MOCVD - that I developed and improved in 1977 while at Rockwell International.

Now, MOCVD is the only technology used for the commercial manufacture of all colours of high-brightness LEDs.

The third part of this trio who won the award is George Crawford, who was also one of Holonyak's students. He led the LED development effort at Monsanto and developed the first practical yellow, or amber, LEDs.

What do you view as your contribution to making LEDs replace the light bulb?

If you took away MOCVD, the LED world would collapse completely up to this point.

There's no other technology in use for creating high-brightness LEDs. It would take a huge research investment to bring a competing technology up to the performance level and efficient manufacturing cost that MOCVD provides.

MOCVD is the winner for the foreseeable future, and I'm pretty happy about that because I did part of it.

When Holonyak left GE to go to the University of Illinois, Bill Packard wanted him to set up the LED research group at Hewlett-Packard.

If he had done that in 1963, he'd have been a multi-millionaire a long time ago.

He chose to be a professor, and he says he'd still choose this route again because he's had so much fun doing research and being at the front edge of a lot of things.

I came back to academia after working in industry for 15 years because of what I saw Nick Holonyak doing in his career.

How did you perfect the process of metal-organic chemical vapour deposition (MOCVD) to grow high-quality semiconductor thin films and devices? And how did it improve LED technology?

In the mid-1970s, Rockwell International was developing the guidance systems for Minute-man missiles.

It was necessary to design a system with radiation-hardened circuits so the missiles could go through these nuclear bomb clouds.

One key feature of these circuits was the need for stability in the conductivity of the substrate. Silicon was the technology of choice, but it suffered when exposed to large amounts of radiation.

My colleague, Harold Manasevit had the idea of growing silicon on a sapphire substrate, which was an insulator from radiation and infinitely stable.

So he developed a technology called silicon on sapphire, or SOS, which was used in the Minuteman missiles.

In 1975, I joined Rockwell. At that time, no one had applied this technology to the growth of high-quality materials such as gallium arsenide.

I began to work on this and developed my own approach and equipment.

By 1976, I had some good devices - solar cells, and in 1977, I created the first semiconductor laser, or LED, made by MOCVD. It was infrared, but it was a high-quality device.

Since joining the faculty of Georgia Tech in 2003, you have begun exploration of nanoscale 'self-assembly'. What is that and how will your research affect this nanotechnology work?

To date, we've been making semiconductors like we did in the 1960s.

Now we're exploring the possibilities of nanoscale self-assembly to manipulate materials at a fundamental level.

Today, we make LED materials on the microscale level. Next, we want to take semiconductor element atoms and assemble them in a different way using rules that we're still discovering.

We're forming assemblies of atoms in sets of tens or twenties, not 10 or 20 millions like LEDs are made today.

LEDs take a large chunk of real estate today. We're attempting to build materials on the order of thousands or hundreds of atoms instead of millions or tens of millions.

To do that, you can't use crude tools or chemicals. You must use self-assembly, or Mother Nature's rules such as those for stress, strain and localised physical features. We need to know how to get her to do this for us.

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