|
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
|
