12/12/2002
Goodbyes
In last week''s column, I made light of an erroneous report of my demise. Two other classmates of mine were mistakenly placed in the same category. Sadly, after posting the column, I learned that a fellow student in another class was correctly listed as deceased. I hadn''t seen Ed Brame for over 50 years but we kept in touch through lengthy Christmas letters. We shared careers in chemistry, both of us taught short courses for the Center for Professional Advancement and we were both active in our professional societies. In our youthful college days, we also shared a love of basketball and once broke into the college gymnasium to shoot baskets - a daring breach of the rules, especially for Ed, a minister''s son. It turns out that we also shared episodes of internal bleeding. Unfortunately, Ed ignored the symptoms too long and died in Shanghai while on vacation with his wife.
Closer to home, last week I attended the funeral service for Andrew S. Jordan, who also died while traveling (in Canada). I first met Andrew in 1966, when he became a member of my newly formed group to provide materials support for the light emitting diode (LED) development effort at Bell Labs. It was clear from the start that Andrew was not going to be an easy individual for me to supervise. Indeed, I take credit for quickly deciding that he was one of those best left to their own devices. Andrew was not a morning person. That fact led a director in another area to suggest that I should force Andrew to report for work on time instead of allowing him to stroll in shortly before noon. Many of his afternoons were spent wandering around just chatting, another habit that annoyed managers who favored more structured work habits.
What they didn''t realize was that Andrew was a night person, whose fertile mind would take those seemingly aimless conversations and every so often turn them into gems. As his supervisor, I would often listen patiently to his ramblings, thinking to myself, "What is this guy talking about?" A couple of months later, he would turn those ramblings into a model or theory or an explanation of some problem of significance to the group. I just looked at a couple of my publications and found an example of Andrew''s contributions. It wasn''t one of his more important contributions (we''ll get to one later) but it illustrates his tenacity and his habit of coming up with something that provided new meaning to someone else''s data.
In 1960, I published a paper summarizing the available data on the solid solubilities of impurities in germanium and silicon. (Solid solubility is just a measure of how much of an impurity will dissolve in solid material, such as silicon.) One impurity was bismuth. Later, before becoming a supervisor, I found that dissolving bismuth in gallium phosphide resulted in yellow- orange light emission and my co-workers and I got a patent on the finding. I also had some solid solubility data on bismuth in gallium phosphide. The solubility data seemed shaky to me but I put it in our July 1966 Applied Physics Letter on the light emission as a sort of throwaway graph with a remark that the data were scattered.
In 1972, I switched to lithium battery work and lost contact with the semiconductor field. I was surprised when, in 1975, Andrew showed me some calculations he had performed using my 1966 bismuth-gallium phosphide solubility data. In July 1976, we published a paper in the Journal of The Electrochemical Society in which Andrew made my data look quite credible. Not only that, but he took the 1960 data on bismuth in germanium and in silicon and somehow manipulated them into a prediction of the solubility behavior of bismuth in gallium phosphide. The agreement was amazingly good.
While this achievement was gratifying to me personally, Andrew is best known in the crystal growth field, where he made a truly seminal contribution that generated worldwide interest. To lay the background for this contribution, let''s review a bit about single crystals. An ideal single crystal is one in which all the atoms are lined up perfectly atom by atom on the sites appropriate to the crystal structure of the material. As with most things in life, it''s very difficult to achieve perfection. Crystals are no exception and a real crystal will contain defects of various sorts.
One type of defect is called a dislocation. There are different kinds of dislocations, such as the so-called line dislocation. To illustrate the line dislocation, imagine a deck of 52 cards, tightly packed. Now let''s slip a 53rd card half way down in the middle of the top of the pack. This will squeeze the tops of the cards slightly out of line with the bottom parts of the cards. Now imagine the cards are planes of atoms. If we stick an extra plane of atoms into perfectly aligned planes of atoms in a crystal, that''s a line dislocation. There are other kinds of dislocations and defects but why worry? Dislocations and other defects typically degrade the electrical properties of devices such as transistors that are fabricated from these single crystals. Simplistically, you might imagine, for example, that an electron whipping along between planes of atoms from one contact to another might be slowed down or even fail to reach the other contact if it hits an atom out of place in a dislocation.
Two of those at Andrew''s funeral service were Alan Von Neida and Ron Caruso. Alan grew crystals of gallium arsenide and gallium phosphide, while Ron studied imperfections in these crystals using so-called etch pits. If you place a semiconductor crystal in an appropriate acid or an alkaline solution that attacks the crystal, the solution will preferentially attack those areas on the surface that are defective. Etch pits visible under a microscope will show up marking dislocations.
Why should dislocations occur? Enter Andrew, looking at the patterns shown in Caruso''s etch pits. Andrew decided there was something fundamental in those patterns. If you''re growing a crystal by the common crystal pulling method, you have a seed crystal that''s relatively cool and you''re pulling the crystal out of this molten gallium arsenide, for example. There are substantial temperature differences along the crystal and across the crystal as you pull the crystal out of the melt. Andrew calculated the stresses set up by these temperature differences and predicted that those stresses would lead to certain patterns of dislocations. His predicted patterns matched Caruso''s etch pit patterns.
Andrew''s elegant papers on the subject garnered international attention and inspired theoreticians worldwide to work on this problem. Attention was paid to reducing the sharp temperature gradients in crystal growth in order to reduce the number of dislocations and grow more perfect single crystals. His work also explained why gallium phosphide crystals had more dislocations than gallium arsenide crystals. (I''m indebted to Von Neida for providing details of Andrew''s work in this area.)
Andrew spanned disciplines with ease. He, like many others caught in the AT&T/Lucent spin-off and roller coaster ride, was forced to find employment outside Bell Labs. He ended up with a unit of AT&T working on reliability problems. I''m unfamiliar with those problems but understand he his work in that field was first class. Like Lance Armstrong, Andrew was first class in the way he fought and won his battle with the same type of cancer while at Bell Labs. Or take the incident in New York City when he found that his briefcase, which contained some treasured calculations, was missing upon returning to his car. It took guts to walk through that neighborhood and try to convince some unsavory characters that he wanted that briefcase. I don''t remember the details but he got his briefcase back.
I didn''t mention that Andrew was a Jew growing up in Budapest and that as a child he and his father would go shopping while bullets were flying. He, his brother and his parents escaped the Holocaust and later escaped from Soviet dominated Hungary. All ended up in America. His brother delivered a very touching eulogy at the service, beginning with "It''s hard to say goodbye to a brother." Also to a colleague and a friend. But I couldn''t help smiling, thinking that Andrew would have appreciated the time of the service, 2 o''clock in the afternoon. He never was a morning person.
Allen F. Bortrum
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