Professor Colin Humphreys, University of Cambridge
Ben - There's a new way to make LEDs and this could slash household lighting bills and help to make clean drinking water accessible to everybody. Professor Colin Humphreys from the University of Cambridge joins us now on the line. Hi, Colin.
Colin - Hi.
Ben - Tell us a bit about this. We’ve had LEDs for a long time. They are already turning up in torches, in home lighting. What’s the new method that you’ve got?
Colin - They’ve been around for some time. They’re not really in home and office lighting and the reason is they’re too expensive. All the LEDs you can buy in the shops now are grown on a sapphire substrate and sapphire is quite expensive. What we’ve done is to develop a method for growing these LEDs on a silicon substrate. In fact we’re growing them on a six inch substrate wafer instead of on a two inch sapphire wafer. That’s going to be bringing costs down by a factor of ten or so, a really big reduction.
Ben - Wow. These LEDs are very energy efficient, I understand. How will it compare to a normal incandescent light bulb?
Colin - They’re very energy efficient and they’re really going to help global warming. In fact, they’ll help it much more than wind power will. In terms of an incandescent light bulb we’re aiming to be twelve times as efficient as a tungsten light bulb and we’re aiming to be 3 times as efficient as a low energy light bulb. Already they’re more efficient than a low energy light bulb.
Ben - Is that for the same brightness as well?
Colin - That’s for the same brightness, absolutely. We want to make them better quality and better bright light than the low energy bright light ones, which as you know are not very popular. They’re a popular cause for divorce in the country now, I’m told, low energy light bulbs!
Ben - Hopefully your gallium nitride LED light won’t be a cause for divorce but I’ve also heard these could be used to make clean drinking water. I understand what you can do with these is make ultraviolet light.
Colin - That’s right so the light emission from the gallium nitride – we actually add some indium to it to get visible light emission. If you add aluminium you can get deep ultraviolet. Deep ultraviolet has certain wavelengths, it’s about 270nm. It destroys the nucleic acid in both DNA and RNA and it stops viruses and bacteria from reproducing so it effectively kills them. If we can make LEDs that emit this deep UV we can kill all known viruses, all known bacteria and you could put a ring of these LEDs on the inside of a water pipe coming into a home in the third world. Water riddled with bacteria and viruses, you can make it harmless. Also it could be useful for our country as well, particularly for third world people.
Ben - And we could use them in hospitals as well to ensure things are sterile without having to go through the chemical cleansing that we do now. As they are so efficient does this mean we can set this up with a solar panel and make this water purification very portable?
Colin - Absolutely. That’s absolutely right. These are very efficient. They’ll run of 4 volts, which is ideal for a solar panel, you have a solar panel and a battery connected as well if you like and then have these connected to that. You have these for lighting in the developing world but also for water purification in the developing world.
Ben - These sound fantastic but what’s different about gallium nitride that allows us to make this seemingly wider range of frequencies? If we can make UV that we couldn’t before. Why is gallium nitride so special?
Colin - Gallium nitride’s called a wideband gap semiconductor. Before it came along the only light emission which you get from semiconductors was in the infrared and in the red and rather weakly in the green and the yellow. Silicon doesn’t emit light anyway. Gallium arsenide emits light and indium phosphate but they’re narrow band gap materials. If it’s a much wider band gap material, gallium nitride itself emits near ultraviolet and then there’s another material called indium nitride which emits in the infrared. If you mix those two together you can get any energy you want from the near-infrared going right through the visible spectrum to near-ultraviolet. If you add some aluminium to it you can go really into deep ultraviolet. This is a new material system. It’s man-made. It can cover this range of the electro-magnetic spectrum that we’ve never had before form a solid state semiconductor.
Ben - This sounds quite incredible. When should we expect to see these on the market?
Colin - For the home and office lighting –scientists always predict thing will happen before they’re going to happen! I think within the next five years, certainly. Maybe two or three years. The UV problem is more difficult to solve. We’ve already got the right wavelength being emitted but the intensity at the moment is too low. We’ve got to push up that intensity. I think realistically that may be 5-10 years. I really believe it’s going to happen.
Ben - Clearly getting clean and drinkable water to everyone in the world is going to be a challenge and I suspect unfortunately it will still be a challenge in those 5-10 years. Good luck, I hope we get them to market as soon as possible!