So, I've put together in, in
a lecture like this, I'm never quite sure how much to go into background.
You guys are all Engineering based off, you can grasp a lot of the concepts.
Some of the areas, though, get very nuanced.
And I tried to pick out some of the key ones, that
you probably haven't seen before, unless you've been exposed to lighting or
LEDs, and kind of go into those a little more detail.
And the other kind of basic physics stuff, I skipped over kind of briefly.
But if you have questions, please stop during my lecture, and
we can go into anything you want to go drill into today.
lighting is kind of an interesting, technology to merge with high-tech.
unlike, internet and wi-fi that's all brand
new, mobile devices which were all brand new.
Lighting has been with us for, throughout the evolution of mankind.
so we have very visceral response to lighting.
For, example, the lighting in this room?
Is realy bad,
[LAUGH],
and could be improved.
but we have a natural, predilection towards daylight.
and bright high scotopic content during the day.
and at night we feel most comfortable, under what
are called warm light settings, especially light coming from below.
And these are things you cannot easily change.
this is stuff that's built into our DNA, so to speak.
and it gets interesting, because when you start to develop the technology
piece, you find that, at the end of the day, there's
an end consumer who really doesn't care anything about the technology.
So it's very different than some of the other high tech sectors, where
you have to instead have a new language to talk about quality of light.
The importance of what can be done with LED technology, in terms
of dynamic control of lighting, or making a luminaire disappear, so to speak.
So a lot of interesting aspect of design.
And health and well-being and this sort of, aspect.
So everybody's an expert in lighting.
And that's what we learned right away when
we started to develop a new business on it.
And tried to disrupt or supplant what people had gotten used to over the last
100 years, like the Edison bulb, which is being phased out, as you probably know.
so lighting fairly fundamental.
It consumes 20% of worldwide electricity believe it or
not, in some cases, in industrial buildings, it's more like
30% of electricity, in industrial buildings is going to lighting.
So it's not a small component of energy consumption.
It's also a very large market.
and so you have a lot of companies interested in either maintaining their
market share of lighting, in the conventional
old companies, like GE, Phillips, and Osram.
And then you have some of the new upstarts, the bigger consumer
electronics companies, trying to figure out how they can get into this market.
so it's a pretty
interesting and dynamic place.
so what I'll, I broke my video into three sections.
So, I'll talk about it LED fundamentals in the beginning.
And, and then I'll transition into lighting
specific concerns to talk a little bit more
about lighting applications, and how we need
to think about LEDs to deploy towards lighting.
And then thirdly, I'll talk about SORAA's strategy,
in particular, what we're doing over here in Fremont.
So LED fundamentals, I can probably go through this pretty quickly, and assume
that most of you guys have dealt
with this in your undergraduate semiconductor course.
But you know, basically we have a semiconductor.
A single crystal a lattice of atoms, that
specify a photonic that specify electronic band gap.
And we can dope the materials, either n-type
or p-type, to provide charge carriers that can under
applied bias, recombine in the active region
of the material, near the p-n junction.
And on the right conditions, electron hole, can recombine and give off
a photon that is equivalent to the band gap at that position.
So the neat thing about LEDs, which is very different then other
conventional lighting sources, is it's fundamentally
non-destructive, and in theoretically 100% efficiency.
it's not quite true today, but some of the numbers that I'll talk about, might shock
you in how good the LEDs are, are getting at this point.
so a very, very different situation then, then, the,
evaporating tungsten filament, or a
mercury discharge, that's exciting phosphors.
And I'll talk about that a little bit in detail, in a minute.
the other aspect we need to consider is that, for unlike a telecon application,
where we're just worried about watts, we have to worry about what our eye sees.
Because in a lighting application, what matters is what our eye sees, and so
we have to deal with luminosity.
And that's the eye response which has a shape like this.
So its peaked in the green we're most
efficient at seeing yellow-green light at about 555 nanometers.
luminosity function which is defined by CIE earlier last
century, defines 1 watt of optical power by 55 nanometers as 683 lumens.
And the rest of the curve has a shape like this, and you see there's
very little lumens in the blue, and a fall off of lumens in the red.
And so, obviously, light sources that are very peaked
in the green, are going to be very efficacious.
We're going to see them very well, but nevertheless, in order to render
colors properly, you need to have the right amount of blue and red.
And so you can't, there's this trade-off, it's a
fundamental trade-off, between light
quality, and color rendering characteristics,
and the efficacy of the light source.
How easily we're able to illuminate a room with it or a setting with it.
and so, knowing that this hasn't been lost on
the lighting community for, for the, the last century.
this slide kind of summarizes in a
situation, the situation with incandescence, fluorescence and LEDs.
So we have here the
wavelength on a logarithmic scale.
and the spectral irradiance of various sources.
For incandescent tungsten radiator, for example, is very much like a black body.
puts the vast amount of its energy in the infrared, where I can not see it.
It's basically a heater.
Again, this is a log scale, so this is a little bit misleading.
But if you look outside this visible spectrum, which is
bracketed by the dashed lines here, 95% of the incandescent
power is going into this region out here,
and so really these these lamps are heaters.
And in fact, I understand that there's a company in Germany, that in order to get
around some of the European bans on incandescent
bulbs, is selling 100 watt incandescents as heaters.
And it's somehow able to get
[LAUGH]
out from underneath these issues with banning the technology.
So, there's interesting loopholes where things can people can play.
But yeah, they're 95% heat.
Only 5% of the power's going to light.
And that's why they're really bad light
sources from an energy conservation point of view.
[COUGH]
the development of fluorescent technology was largely you
know, motivated to try and get around this problem.
To put all of the energy of the light source, where our eyes can see it.
So this grey curve here shows line admitting
phosphors, which are fairly popular in florescent bulbs.
and these are excited by a mercury discharge.
And a mercury emission is very efficient, about 80% efficient from the electrodes
going in to ignite the mercury line at 254 nanometers.
But here, we have five volt photons, that we have to convert to the visible.
Which is an average of about two and a half volt photons.
So there's a, there's a fundamental 50%
penalty in efficiency, built into the fluorescent technology.
So we're not expecting to see fluorescent
bulbs near, you know, 800% theoretical limit,
based on, at least, not based on mercury transition.
There are some other lighting technologies that I won't go into, into detail.
But if you have questions about em, we can talk about it, later.
But these are the mainstay three for, especially for
residential, and for the bulk of, commercial lighting as well.
with LEDs, we have the opportunity to put all the lighting exactly where we need it.
the most common approach, and I'll mention more details
about this, is to take a blue or violet
emitter and pump phosphors that are nearby in energy, so the stokes loss is very low.
another opportunity would be to take, you know, individual LEDs at
different colors and, and combine them together and make white light.
But the interesting thing is that of course, you
know, again on paper daily, these are the ultimate lamp.
Nick Holonyak who invented the red LED in
1962, in fact, we just celebrated the 50th year
anniversary of the LED in Illinois a couple weeks ago.
wrote to describe this in a paper back in
2000, about how the LEDs could be the ultimate lamp.
And theoretical efficiency is 100% or at least, again, possible on paper.
Another interesting thing about LEDs is that
in the case of special artifacts like art.
The Mona Lisa in the Louvre.
When you, you have to illuminate these
things, for people to enjoy them. And guess what?
They don't like IR, they don't like heat, and they certainly don't like UV.
Because the, the, articles can be destroyed
over time, by having proton energies too high,
or conditions that are too dry or too
much irradiated power that's not useful for light.
So, the LED or the Mona Lisa's been lit by LED, I think for the last already 12
years before the technology was really ready for it,
because they were so concerned about preserving these these artifacts.
And so it's it's very powerful situation to be where we can control the spectrum
exactly as we want, deliver light only where
our eye sees it, and not anywhere else.
No heat.
No harmful ultraviolet radiation.
there are basically two material systems that drive LED technology today.
There's a lot of research in other materials.
There's research into organic LEDs,
which I won't talk about.
that are pretty far behind in organic LED based technology.
These are the two mainstay material systems.
They're both compound III-V semiconductor systems.
the earlier system developed was a free phosphide system on gallium arsenide.
So gallium arsenide substrates have been around for quite
a while, driven by telecomm applications and RF applications.
And turns out, sure enough, that you can provide the rights to a geometry
of aluminum galliminio phosphide, and maintain a
lattice match to the cubic galiminarsnide lattice.
And grow, you know, defect free materials.
And with gallium and aluminum substitution, you
can change the band gap of the materials.
So you can move anywhere from you
know, aluminum indium phosphide, to indium gallium phosphide,
from the red towards the yellow, and provide LEDs in that wavelength regime.
Around two electron volts give or take.
one thing you see right away, is that the band gap engineering potential is fairly
small you quickly hit a rail with indium luma phosphide, at a fairly low
voltage 2.1 or so volts.
And if you have an emitter that's 1.9 to 2 volts, you only
have about 100 millivolts of band gap
engineering for carrier confinement, and designing the
device to operate efficiently, and that's a problem.
So there are issues with gallium gap like temperature,
high temperature performance and stuff that are not so great.
but nevertheless, the best readily LEDs today, are based
on this material system, and even into the red-orange.
all the LEDs you see in the backs of cars,
or in red traffic signals, are based on this material system.
the other material system and really the workforce
for lighting, is the gallium nitride or any
m-, gallium nitride material system.
it's a little bit different situation, so there is no native
substrate, and I'll talk about, about that a little bit later.
It's been kind of a big deal.
unlike
and silicon they can be grown from the mell, and
[INAUDIBLE]
can not be grown from the mell, and it's, proved to be a challenge for the industry.
So the industry actually ended up evolving by figuring out
ways to put down galli-nitrate on form materials, like sapphire.
And there were some very key, events in the late 1980s in Japan,
figuring out how to put down single-phase gallium nitride material on sapphire.
Figuring out how to make that material p-type, by magnesium doping, and with
those building blocks, the first wave of
LED technology on gallium nitride was developed.
And that's more less what we enjoy today, is the fruits of that work.
but there' s some but there's clearly some differences.
So, in order to get into the visible spectrum, the
violet, blue, green, we have to basically move to indium
gallium nitride. We need to reduce the bandgap energy.
And as we do that, we walk off of the gallium nitride line.
So, the gallium nitride is deposited on sapphire.
now you have gallium nitride lattice constant, and
when you start to introduce indium nitride into
the lattice, you have a bigger atom that
doesn't fit, and so you build up impressive strain.
The other thing that's interesting about NGAN, is that
this material is a worksite material, so it's not symmetric.
And so, as you grow the materials,
typically you're growing on the basal plane.
So you have an elongated hexagonal lattice, and
as you grow layers you with different material properties,
you have spontaneous and piezoelectric polarization fields that build
up in the structure, so the bandgap is distorted.
We've built in fields that are pushing carriers around in ways that
are complicated, and make understanding device physics of a gam device fairly,
can be confusing and also result in performance limitations.
but nevertheless gallium nitride based devices with indium gallium nitride
active emitters emit all the way from 365 nanometers, up to 550 or so nanometers.
And you can get all of those emitters in those wavelength regimes.
there's also a lot of work on DUB, I wont
talk about that, but either a base on Gallium Nitride or
even more likely Aluminum Nitride spanning this regime.
And there is interesting appli-, applications
like water purification disinfection at very short
wavelengths like 276 nanometers or so that
are also available with this material system.
as I mentioned before, one could make white
by mixing red, green, blue, yellow LEDs, for example.
And of course, you could, if they were on different
track drivers, you could have a spectrum that's changing with time, or with
music, or during a time of the day however you want to do it.
And there's some, certainly, products out there that make use of this.
in terms of just producing a high quality
static white, it is fairly complicated to do that.
you need more than one driver.
And an application as cost-sensitive as lighting.
because people like, don't like to pay money for lighting
if they don't have to.
it can be difficult to have
a, a, inexpensive solution based on multi-primary.
Much more common ly done to produce white light, is using down-conversion materials.
So what we mean by down conversion is, take a blue or violet photon of three
volts or so, to 1 8th 3 volt's,
and down convert that to the visible, using phosphors.
And so a typical this is from a paper by
Phillips a few years ago, when I was there just
shows a cartoon of what we have. We have an LED chip on a package.
And in this case it's a blue emitter.
and it's surrounded by, particles of a,
two phosphors, a red phosphor and green phosphor.
And by mixing the primary blue light, and the secondary emmision
from the red and green phosphors, you can have white light.
And, with the right choice of materials, you
can build up a wide range of spectra there.
And the beautiful
thing about this device is very simple. You have one LED.
One driver the down-conversion is happened, you know,
happens built in in the assembly of the device.
And with the right kind of materials, you can, you
can provide interesting spectrum that are useful for lighting applications.
and so by far, 90 plus percent of white LEDs today are using this approach.
So, LED luminous efficacy now.
This is lumens per electrical watt has
increased exponentially over the last several decades.
So again, 50 years ago the first emitter was
demonstrated by Nick in the GE Research Labs in 1962.
0.2 lumens per watt or so, they were extremely inefficient.
but the material systems continue to be developed.
the eventually, the gallium
arsenide substrates were removed to provide
for a fully transparent lumen gallium
[INAUDIBLE]
phosphite emitters.
And so you had red emitters now, red
and orange emitters approaching 100 lumens per watt performance.
you had the inground materials which came on really in the
90's with their performance coming up rapidly behind the red emitters.
And around last decade, you have several
emitters now crossing the 100 lumen watt barrier.
As a reference point, you know,
incandescent bulb that you're all familiar with, 60
watt bulb, is about 15 lumens per watt.
Again, this is this 95% here.
tungsten halogen is a little bit better
because the filaments run a little bit hotter,
a little bit brighter and you see more efficiency there, but it's not much more.
It's on the order of 20 lumens per watt at the source level.
Fluorescents good fluorescents can approach about 100 lumens per watt.
A more typical number for a compact
fluorescent, you're going to source something like 50.
there's also a high-intensity discharge lamps which
are getting traction, especially in retail sectors.
They're pretty ra-, efficient sources.
More than a 100 lumens per watt, and they put out a ton of light.
They u-, they use fairly complicated electronic
ballasts, to be able to ignite the discharge.
And they have interesting burning characteristics.
The color can change over time.
The light output is, like, kind of non-uniform over time.
and they're tend to be large.
So in small applications it, they don't work nearly as well.
the US Department of energy has a road map on taking LEDs
out to 200 and 200 and 250 lumens per watt or so.
Before they asymptotically roll over, and as a
reference point a theoretical limit for any reasonable spectrum.
based on colorant rendering that we would all consider
reasonable for illumination, is about 40 lumens per watt.
So you're not going to see a source better than that, that's truly white.
Yeah I think that's it for that slide.
So you know, and haven't really gone much into the lighting stuff yet.
I'll go into that in the next section.
but you know, even before the end of the last
decade, you see LED's penetrating massively into all of these applications.
The cellphone market,
displays, LCD TV's, jumbo trons like AT&T Bell Park the back of automobiles.
also, you know, cell phone flash for a camera phones,
were a driver, believe it or not, for LED technology.
the market was, at the end of last year, about $12.5 billion, again, with
a vast majority of the applications not
being illumination, but being all these other things.
LCD backlighting being a very, very large one.
the compact fluorescent the, I should say the cold cathode fluorescent tubes, really
started to fall away with LEDs around the middle of the last decade.
because the LEDs had basically were getting better and better, in terms
of efficiency, cost was going down, and it allowed very thin form factors.
So you see all these advertisements for really thin LCD TVs.
That's possible, it's made possible, by LEDs.
The fluorescent technology could not
enable that.
[MUSIC].