The 2014 Nobel Prize in Physics
nobelprize.org
nobelprize.org
It's just a shame that that the key dude in all this got the shaft for years. The performance of these LEDs was a big deal at the time in a lot of different industries, so it was obvious that lots of money would be flowing around... there really was just no need for anyone to deny him his, well deserved, part in that.
How much are they now!
Blue ones are used, at least around my area, to decorate things.
Don't let the "blue LED" headline fool you. This discovery did not just enable blue LEDs but a whole range of nitride-based devices. This includes, but is not limited to:
* LEDs for a wide range of colours, including white LEDs for general lighting
* blue (and other colour) laser diodes (e.g. Blu-ray)
* solar cells (nitrides show good radiation resistance, making them of specific interest for space applications)
* high electron mobility transistors (power converters are a big application, but these are useful for a huge range of other applications too e.g. radar)
* potential for biosensors (it's non-toxic/biocompatible and can be functionalised)
* better UV emitters (and all that entails, e.g. water purification, or potentially lithography)
and more besides. It really is an enabling technology, though obviously there are alternatives for a lot of these applications too. Blue LEDs just started this all off.
Edit: LED lasers that enabled things like the Internet (Optical fibers often use DBF Lasers) were invented by Alferov and Kroemer that also shared the physics Nobel price in 2000.
http://www.nytimes.com/2005/01/12/business/worldbusiness/12l...
Not joking.
I had a 2007 laptop festooned with about ten of those eye-piercing blue spots, but it's hardly fair to blame the inventor for the poor use of his work.
Alfred Nobel had it worse - he did make an explosive ...
While I'm happy for them, and am in no way qualified to question the Nobel committee, it just doesn't strike me as an "outstanding contribution to the field of physics".
You have to consider it within the context of the intention of the Nobel prize, which is to reward the "invention of greatest benefit to mankind". So perhaps it's not fundamental physics per se, but it's certainly in the spirit of the prize. [Disclaimer: I work on this stuff, and was lucky enough to see Nakamura talk just recently. So I'm definitely biased!]
Edit: Also, coming from a background where I've gone through the whole gamut of physics, chemistry, materials science, engineering and the rest, I have to say that there's a tendency to undervalue the contribution from actually going from something that's theoretically possible to actually practical. In some respects, the fundamental physics is the 'easy' part–nice neat equations describing nice neat systems. Actually trying to make them, when you're up against entropy introducing all manner of crystal defects and impurities and what-not, is a whole different story. And it's so complex, and the tools you use so rudimentary, you can very much feel like a blind man feeling around in the dark just trying to understand what's going on, and what you've actually managed to make. To go from that to a functioning, reproducible device? It definitely deserves recognition.
So, to start at the beginning: how do we grow these things?
At the heart of every LED is a crystal. For blue LEDs, this crystal is gallium nitride (GaN). How do we grow these crystals at scale? This achievement is behind this Nobel prize, but it's far from a solved problem even today. They found out you could grow GaN by flowing hot gasses containing Ga and N on top of an artificial sapphire film, which would act as a template for the crystal to grow. The problem is that GaN crystals and sapphire crystals are slightly different sizes (the gaps between their constituent atoms is different) so they don't match up exactly, and this resulted in a lot of strain and defects in the GaN crystals–but sapphire was the best we had, and it worked. The trouble is, sapphire isn't great: it's expensive and you can only make small crystals.
The big push now is to find a way of growing GaN on top of silicon. This would make it a lot easier to grow larger crystals and would also make it a lot easier to incorporate GaN into silicon-based devices. But growing on silicon comes with its own problems, so it's even harder to grow high quality films. Specifically, cracking as the crystal cools from its growth temperature is a big problem because the thermal conductivity of silicon and GaN is so different.
There's also a push to try and grow GaN directly from a liquid, which would be more like how we grow silicon 'from scratch' (rather than growing on top of a template). This shows a lot of promise but it's a long way from commercial viability yet.
I'll try and come back and comment on some other issues later on if there's interest :)
I work on biomolecular crystallography and nucleation is half the battle! The other half, used to be size, but thanks to microbeam beam lines, at synchrotrons like APS, we can get away with very tiny crystals for X-Ray diffraction data.
I am fascinated by the idea of using semi/synthetic materials as seeding agents. But then again, biomolecular crystals have huge unit cells compared to semiconductors. People have tried zeolites in the past, but surprisingly a random speck of dust sometimes works better than the best designed substrate.
This is exactly what's often done. It's all about scale fundamentally. It's slow to grow crystals, they have to be very high quality single crystals, and they can't have even the slightest trace of impurities, and ideally they're going to be large and easy to process too. If an alternative substrate is also hard to grow at scale, it's not going to work. But I don't want it make it sound like it's just a scaling issue, because to my knowledge better substrates haven't been found even as a proof of concept. It's not just lattice parameters, but a whole host of other things too. But people are still looking :)
> People have tried zeolites in the past, but surprisingly a random speck of dust sometimes works better than the best designed substrate.
Hah, that sounds both incredibly frustrating and good fun!
By the way, your series of posts on this topic have been superlative—many thanks.
> They found out you could grow GaN by flowing hot gasses containing Ga and N on top of an artificial sapphire film, which would act as a template for the crystal to grow.
This must be what [3] refers to. Mix molten gallium with nitrogen at 100 atm, 1000 ˚C. Alternatively, mix gallium with ammonia. Get a powder of GaN, then vapor deposit it into layers.
> The problem is that GaN crystals and sapphire crystals are slightly different sizes (the gaps between their constituent atoms is different) so they don't match up exactly
Right, several articles mention matching lattice constants. Seems to be a big problem. In fact, [2] mentions that the first substrates used for growing GaN were sapphire, zinc oxide, and silicon carbide. A chart [4] shows lattice constants, which I don't fully understand, but GaN's 3.186 Å is pretty close to SiC's 3.086 Å. So this seems to make sense.
How do you compare a single lattice constant like ZnO: 4.580 Å with a pair like GaN's 3.186 Å, 5.186 Å?
[1] https://en.wikipedia.org/wiki/Light-emitting_diode#Ultraviol...
[2] https://en.wikipedia.org/wiki/Gallium_nitride
[3] https://en.wikipedia.org/wiki/Gallium_nitride#Bulk_substrate...
[4] http://sector7.xray.aps.anl.gov/calculators/crystal_lattice_...
Not quite. If you want something to search for, search for "metalorganic vapour phase epitaxy" (MOVPE) or "metalorganic vapour deposition" (MOCVD).
> How do you compare a single lattice constant like ZnO: 4.580 Å with a pair like GaN's 3.186 Å, 5.186 Å?
This is a harder question than it might seem!
You can easily calculate a lattice misfit as a percentage if the crystals are the same shape: (a_substrate - a_film)/a_film. If it's low, the films will be strained, if it's higher then the films will have to relax through some deformation process resulting in disruption and defects at the interface. It's a complex process, and there's no easy rule for what will happen (keyword to search for is "Matthews Blakeslee" who came up with a model to predict how thick a film could be for a given lattice misfit before you get these defects, but in practice it's quite limited).
Care must be taken to directly compare lattice parameters though. To pick a simple example, imagine you have one crystal with a lattice parameter exactly twice that of another. On paper, that'd be a lot of misfit, but because they tile perfectly in practice it might work really well. Likewise, you can imagine lining up two square crystals, you could imagine being able to line up the diagonal of one crystal with the sides of the other crystal if one lattice parameter if the ratio of their lattice parameters is 1:sqrt(2). So it's not as simple as just looking to see how similar two numbers are, you have to consider the geometry of the crystals too.
This is where it gets a little complicated. For your specific example of ZnO and GaN, the ZnO value you have is for cubic ZnO so its three lattice parameters are the same (a=b=c like the sides of a cube) which is why only one is quoted (a = 4.580 Å) whereas GaN is hexagonal (a=b!=c) which is why two are quoted (a = 3.186 Å, c = 5.186 Å).
[Aside: GaN is often grown on its c-plane, in which case we can neglect the c parameter for working out the lattice misfit. This is something that's difficult for me to explain in words, but if you're interested in understanding it a bit better, search for "Bravais lattices" so you more easily visualise what these lattice parameters refer to. This means we only need to consider the a values when working out the misfit.]
So you'd want to compare the 4.580 Å value to the 3.186 Å value and ignore the 5.18 6Å value. But because the GaN crystal is not just a different size but also different shape to the ZnO crystal (hexagonal vs. cubic), it's actually more complicated. However, luckily for you, ZnO also exists in a hexagonal form just like GaN and in that case has lattice parameters a ~= 3.25 Å and c ~= 5.21 Å, so the misfit between ZnO and GaN in this case would be about 2%?
If you're curious, it seems like people do grow ZnO on GaN and vice versa, so you picked a good example to ask about :)
[Edited a few times for clarity.]
In the crystal, we have two types of particles flowing around. Electrons and holes. Holes aren't 'real' particles, but they still exist: much like bubbles in a bottle of water. It's an awkward analogy, but we can imagine two bottles of water: one that's completely full except for a few bubbles, and another that is higher in energy that's almost empty apart from a few drops of water. These drops of water sloshing around are the electrons moving through the crystal. What happens when an electron (water droplet) and hole (bubble) meet? They annihilate each other, and in the process give off a little spark of energy in the form of a piece of light. For gallium nitride, the light's blue because of the difference in energy between the electrons and the holes.
To get higher energy light (more blue->purple->ultra violet) we can replace some of the gallium with aluminium. To get lower energy light (green) we replace some of the gallium with indium. So far, so good.
One of many outstanding problems though is that LEDs have much poorer efficiencies when we want to emit green light. Lots of different combinations and permutations have been tried, but none are great, and we're still looking for a better solution–this might be in the form of finding a brand new material, or of growing nitride-based crystals in more unusual forms, such as nanowires (imagine a forest of crystals standing on a sapphire 'floor') or quantum dots (tiny little pyramids). This can help because electrons act in very different ways when they're confined in certain dimensions, e.g. if they can only move in along a straight line, and this can be exploited to make better devices. So lots of people are trying this, not just for green LEDs, but for all manner of different devices.
So this is what we do when we want to intentionally change the colour that's emitted. But there's lots that happens to unintentionally change the colour too, which is a problem if you're trying to make thousands of light bulbs that should all look the same! This is the result of much more subtle problems that exist on the very smallest atomic length scales...
I do definitely agree that there is not enough appreciation for the boots-on-the-ground aspect of science, and that those who do it deserve more recognition.
Many groups were working hard on GaN/AlGaN systems at the time, as well as various ternary/quaternary permutations. Kudos to the winners for making it happen. Some pretty big doors were opened.
"...the charter, which is then illuminated with LED lights ranging from the ultraviolet at a wavelength of 365 nm, through the visible region, and right up to a wavelength of 1050 nm in the infrared region."
Like how Einstein got the Nobel for his work on the photoelectric effect? It might have been "more valid" but it was not his most important work and the Nobel Committee got heat for making that call too.
You need to understand a bit more of the context then, which is: the Nobel prize is paid from the interest accumulated by Alfred Nobel's fortune, which is invested in bonds. Alfred Nobel got his fortune by, among other investments, inventing dynamite. Dynamite was not a breakthrough "new idea" -- the explosive in it was nitroglycerin. The short version of the story is that a nitroglycerin explosion killed Alfred Nobel's brother, and it was being banned everywhere in general due to accidents, because explosion can be triggered by physical shocks. Nobel reasoned that it could be made much safer if it couldn't move around so much, and so he ordered a bunch of a locally-abundant porous rock substance and soaked that in the nitroglycerin (we would now say that the "diatomaceous earth" acts as a "stabilizer"). He patented that combination and sold it as stronger and safer than gunpowder for blasting, and it sold like hotcakes.
Due in part to this history, the Nobel in physics is seldom awarded for a theoretical breakthrough alone. Hawking's work on black hole radiation has changed theoretical physics and cosmology immensely, but we haven't observed it coming off of a known black hole, so he's widely viewed as ineligible for a Nobel prize.
Similarly the discovery of graphene was not issued for the work done on it in the 1940s, 50s, 60s and 70s -- it was given for work done in the early 2000s which allowed a lot of graphene to be made cheaply: it turns out you can use scotch tape on a block of graphite to tear off a bunch of stuff, some of which is individual layers of graphene; it helps to fold the tape on itself over and over to try to get more and more little "islands" of it since individual monolayer chunks are super-rare. The key aspect of their work, less-reported in the news but essential, is that those "islands" of graphene have a certain iridescence to them when they're on the right sort of backdrop (a sheet of 300nm-thick silicon dioxide), so that you can see them with an optical microscope.
There's two parts to it: game-changing technology. It's not enough to be theoretically right. In Einstein's Nobel presentation speech, they breeze through relativity with "this pertains essentially to epistemology," and they make a little mention to his huge contribution to the burgeoning field of colloid chemistry (which ultimately proves that atoms really exist and gives you a way to measure how big they are). Instead they go straight to his quantum work: his explanation of the photoelectric effect and his explanation of why the specific heat of metals is about 3R, where R is the gas constant. He wins because he kicked off the field of quantum photochemistry, which was suddenly making lots and lots of strides in understanding the world; and because his photoelectric laws were "extremely rigorously tested by the American Millikan and his pupils and passed the test brilliantly".
Seen in that light, the Blue-LED discovery (how to grow GaN crystals) which opens the way to all colors of LEDs and all sorts of gallium nitride tech, is actually pretty much exactly a Nobel discovery. For example, in my Master's program we would talk about experiments on a 2-dimensional electron gas (2DEG), and the physics thereof. The stock example was AlGaAs/GaAs (the LED material for red/green LEDs, gallium arsenide with a layer of aluminum-gallium arsenide) where they were first observed. But, there was a bit of interesting discussion as well about doing the same with AlGaN/GaN, which has a higher band-gap and, if I recall correctly, needs less (no?) doping to do interesting things.
I tried to find a graph of inflation adjusted lighting prices, but found some interesting links:
http://www.npr.org/blogs/money/2014/04/25/306862378/episode-...
http://en.wikipedia.org/wiki/Timeline_of_lighting_technology
It was only a prise when Obama got the Nobel Peace one.