5 ms·

> 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 p

by Osmium 12y ago

> 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.

DodgyEggplant 12y ago
Is it possible for you, with the HN forum limits, to describe some such interesting major issues with LED (for a physics illiterate)?
- Osmium 12y ago
  Sure. I can give a flavour of some of the issues that people are interested in within the nitrides, but it wouldn't be an exhaustive list... 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 :)
  - shiven 12y ago
    What about using nanomaterials as seed/substrate for crystal growth? Design the unit cell to the exact dimensions? Or use the (imperfect) GaN crystals to grow incrementally better crystals over multiple rounds? 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.
    - Osmium 12y ago
      > Or use the (imperfect) GaN crystals to grow incrementally better crystals over multiple rounds? 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!
      - mcmancini 12y ago
        Is Ostwald ripening a problem?
        Osmium 12y ago
        Not specifically. I haven't really heard it mentioned, but I don't actually do growth myself. It's mostly Stranski-Krastanov growth with islands growing until they coalesce. There's not really any significant flow of atoms between islands to my knowledge. What's your interest in it?
- Osmium 12y ago
  So, the next question, is why are these LEDs blue? And what if we want a different colour? 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...
chton 12y ago
I've never heard about "invention" as such being a part of the intention of the Nobel prize before, but apparently you are correct, it was mentioned for physics specifically in Nobel's will. I suppose I never made the connection because giving the prize for an invention as opposed to a discovery is very rare. That resolves many of my reservations with this year's winners. 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.
- jpmattia 12y ago
  To amplify, it strikes me as in the spirit of the prize for the scanning tunneling microscope (STM). All of the conceptual pieces were present, it was not a huge intellectual leap to put it together. That said, actually working out the details of the tip and controller etc to produce the beautiful results was, well, you knew it was sublime when you laid eyes on it. 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.
  - chton 12y ago
    I don't consider it the same class because an STM is a scientific instrument. It is used to perform more experiments, and leads directly to an increase in knowledge. Blue LEDs themselves, while definitely a big achievement, don't add much to the body of knowledge.
    - l4cr0ss 12y ago
      I disagree. Look, in another article here on the front page, these blue LEDs are directly involved in an increase of knowledge: "...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." https://news.ycombinator.com/item?id=8421623 https://news.ycombinator.com/item?id=8421623

by Osmium 12y ago

DodgyEggplant 12y ago

Is it possible for you, with the HN forum limits, to describe some such interesting major issues with LED (for a physics illiterate)?

Osmium 12y ago
Sure. I can give a flavour of some of the issues that people are interested in within the nitrides, but it wouldn't be an exhaustive list... 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 :)
- shiven 12y ago
  What about using nanomaterials as seed/substrate for crystal growth? Design the unit cell to the exact dimensions? Or use the (imperfect) GaN crystals to grow incrementally better crystals over multiple rounds? 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.
  - Osmium 12y ago
    > Or use the (imperfect) GaN crystals to grow incrementally better crystals over multiple rounds? 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!
    - mcmancini 12y ago
      Is Ostwald ripening a problem?
      - Osmium 12y ago
        Not specifically. I haven't really heard it mentioned, but I don't actually do growth myself. It's mostly Stranski-Krastanov growth with islands growing until they coalesce. There's not really any significant flow of atoms between islands to my knowledge. What's your interest in it?
Osmium 12y ago
So, the next question, is why are these LEDs blue? And what if we want a different colour? 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...

chton 12y ago

I've never heard about "invention" as such being a part of the intention of the Nobel prize before, but apparently you are correct, it was mentioned for physics specifically in Nobel's will. I suppose I never made the connection because giving the prize for an invention as opposed to a discovery is very rare. That resolves many of my reservations with this year's winners. 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.

jpmattia 12y ago
To amplify, it strikes me as in the spirit of the prize for the scanning tunneling microscope (STM). All of the conceptual pieces were present, it was not a huge intellectual leap to put it together. That said, actually working out the details of the tip and controller etc to produce the beautiful results was, well, you knew it was sublime when you laid eyes on it. 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.
- chton 12y ago
  I don't consider it the same class because an STM is a scientific instrument. It is used to perform more experiments, and leads directly to an increase in knowledge. Blue LEDs themselves, while definitely a big achievement, don't add much to the body of knowledge.
  - l4cr0ss 12y ago
    I disagree. Look, in another article here on the front page, these blue LEDs are directly involved in an increase of knowledge: "...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." https://news.ycombinator.com/item?id=8421623 https://news.ycombinator.com/item?id=8421623