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09/02/2011
Irene's Darkness and Lighting up the Phone
CHAPTER 13 - Irene and LEDs
It was an August that I'm sure we in New Jersey will long remember. A couple weeks ago, I had just finished playing golf on our local 9-hole par 3 course and was surprised to see scores of people, most on their cell phones, standing around in the small parking lot. I assumed there must have been a fire drill in the building across the street. However, when I got home I found my wife very upset, saying that our house had been shaking and she was afraid it would collapse. Hey, we in New Jersey don't normally feel earthquakes of that intensity, let alone one as far away as Virginia.
But the earthquake was a mere blip compared to hurricane Irene, which some say the media and our political leaders "overhyped". My wife and I certainly don't share that view; and we are among the very lucky ones. We had power, unlike most in our neighborhood, including our next door neighbors, who have been out of power for 6 days and counting. While the winds were not as bad as expected, the rain was unending, landing on ground already saturated from previous deluges. Across the street, a tree fell in the neighbors' backyard but missed the house.
Not so lucky were our neighbors around the corner. A large tree fell, ending up in their bedroom just inches from their bed in which they were sleeping. Thankfully, they were not injured. However, to compound their disaster, they were without power and their finished basement was flooded without the sump pumps working. As if that weren't enough, water was pouring into their living room from their fireplace!
As for us, when I said we were very lucky, it was in relative terms. I think I mentioned in a column last year that we had installed a water management system in our basement at a cost of $14 K. The two sump pumps and French drain performed beautifully in a number of very heavy rain falls and we had carpeting installed in our basement rec room. With our power intact, the two sump pumps were doing an admirable job during the hurricane, working almost continuously pumping water, and I was feeling comfortable. Then a last band of downpours arrived; the pumps were overwhelmed and enough water came in that our carpeting was soaked. The next day we were informed that the carpeting was not salvageable and $909.50 later, we said goodbye to our soggy floor covering. Looking on the bright side, had our power gone out, we would have had several feet of water in our basement and the damage would have been much worse. And we really feel fortunate when we view those scenes of flooding in neighboring Jersey towns or especially up in Vermont.
Well, I had really planned to begin this column with some of the space news from NASA. There was the possibility of flowing water on Mars and the release of an amazing photo showing two colliding galaxies. If you saw the picture one galaxy happened to be oriented edge-on while the galaxy below it was oriented full face-on, so to speak. The two galaxies formed what NASA termed a gigantic "exclamation point".
But what really got my attention were two discoveries made by NASA's Wide-field Infrared Survey Explorer (WISE) mission. One was a so-called Trojan asteroid that orbits around the Sun in the same orbit as do we Earthlings. It's worth searching the term "Trojan asteroid and NASA" and viewing an animation showing the earth and this little thousand-foot asteroid in their orbits around the sun. The asteroid sort of spirals around our common orbit but apparently, we will never collide with it.
In addition to that cool discovery, WISE has come up with another cool finding. I mean it's a really cool discovery, a half dozen or so Y-dwarfs, star-like objects with temperatures lower than our body temperature. These "cool stars" are something that astronomers have been searching for for years. These "failed stars" are bodies that never got large enough to generate the pressures and temperatures necessary to get those nuclear fires going that keep our sun and other stars glowing for millions or billions of years.
Well, I guess I'll return to my memoirs. Last month I ended with dropping of my work on germanium and silicon and striking out on other materials such as garnets and tungstates and other materials. It was not a rewarding period, with no publishable results. However, in the early 1960s, probably 1963, I learned that Carl Frosch and Lincoln Derick had built a high-pressure apparatus that allowed them to make ingots of the compound gallium phosphide, GaP. (Frosch and Derick, you may recall from an earlier column, had one of the most valuable patents in Bell Labs history with the invention of the oxide masking technique that proved crucial to the manufacture of the ubiquitous silicon chip.)
I thought it might be interesting to grow gallium phosphide from solutions in various metals. So, I got some chunks of GaP from Frosch and Derick and, with my assistant, Mike Kowalchik, took these chunks and sealed them in fused quartz tubes with gallium, a low-melting element. When heated in a furnace, the GaP dissolved in the gallium and, on cooling, the GaP precipitated back out of solution, typically in the form of relatively flat, diamond-shaped crystals. I knew that Murray Gershenzon was working with David Thomas on some sort of optical properties of GaP and gave him some of the crystals. Whoa! That changed my life.
Gershenzon and Thomas were looking at something called photoluminescence. When some materials are illuminated by a light source they will radiate light back out at different wavelengths than that of the light source. Our GaP crystals turned out to luminesce quite brightly and showed a large number of lines in the resulting spectra. John Hopfield, a Bell Labs theoretical physicist, showed that these lines were associated with pairs of impurities in the gallium phosphide. Soon, I found myself growing crystals with various pairs of impurities such as zinc-sulfur, zinc-selenium, cadmium- tellurium, etc. I learned from Thomas and his assistant, Ernie Sadowski, how to read and interpret the spectral plates with all the lines on them and found myself, a lowly chemist, co-authoring a couple of papers in the prestigious physics journal, Physical Review. In one paper, I even found an error in Hopfield's equation for the energies of the lines in the spectra. It was an insignificant error but for an experimentalist like myself, it was delightful to spot an inconsistency in a theoretical physicist's work.
Meanwhile, my old buddies, Ralph Logan and Harry White, were looking at the possibility of using GaP as a material for light-emitting diodes, LEDs. In addition, Frosch and Derick were also starting to grow GaP by a vapor growth technique. However, our solution grown crystals were proving to be superior when it came to brightness. In the early days, we had to look through a microscope to see the light coming out of our diodes. Elsewhere, at RCA and IBM, there was also work on LEDs and at RCA, a fellow by the name of Nelson had come up with a "tipping" technique for growing the p-n junctions needed to make a diode.
This tipping technique essentially involved a furnace mounted on a swivel so that you could place a tube containing a crystal or wafer of, say n-type material, at one end of the tube and the materials to make p-type material at the other end of the tube. Heat the tube so that a solution forms at that end, then tip the furnace to allow the solution to run down over the substrate; by cooling the furnace, a thin layer of p-type material grows on the substrate to form the p-n junction. Tip the furnace back so the liquid runs back off the wafer or crystal and cool the furnace down to room temperature. Remove the wafer with the p-n junction and cut it up into little pieces, attach suitable wires/contacts, and you've got LEDs.
You may recall that I said last month that I transferred out of Carl Thurmond's area so as to strike out more on my own. When my solution-grown GaP proved to be potentially useful LED material, Thurmond asked if I wouldn't set up tipping in my lab to provide the solution-grown material for a major LED effort. At first, I was reluctant. After all, the tipping method was invented at RCA and I wouldn't be doing anything new or novel. However, I agreed, partly due to the fact I would again enjoy working with Logan and White. So, once again I was the materials supplier for a device effort.
Of all the projects during my Bell Labs career, the LED effort was the most enjoyable, partly because of instant gratification. Any progress was evident almost immediately. When we made our tipped p-n junctions, we could just stick an electrical contact down on the sample and see whether the light was bright or not. It was a good indication as to whether Logan and White could make good LEDs. In contrast to my later work on lithium batteries, the main measure of success was how long a battery would cycle and it would take weeks or months to know whether I had made any progress.
Sorry, I find myself just rambling on and I think the effects of Irene have addled my brain. Before I stop, I'll complete this phase of my Bell Labs work by noting that Logan and White ended up making red LEDs that were bright enough to actually light up the push buttons on a telephone with no need for extra power other than that available on the Bell system phone lines. They made such a phone and hooked it up onto the Bell System, the first phone to incorporate LEDs.
OK, I'll stop here, listening to the sound of generators running in the houses that still have no power. Our cleaning lady is here telling us a harrowing tale of how her son and his father-in-law on Long Island foolishly braved Irene to save their boat and then rescued a man clinging to a rooftop of a building that later partially collapsed. No, Irene was not "overhyped"!
Next column, hopefully, will be posted on or about October 1.
Allen F. Bortrum
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