A Half-Century Journey in Research— Applying Physics for the Benefit of Society —Izuo HAYASHI

Abstract
This is an outline of my technical activities
during the past half century, during which I
examined ways to apply physical concepts into photo-electronic devices for the benefit ofsociety. The original story was presented lastyear at the Kyoto Prize Ceremony, describing
my activities to the general public in layman’s
terms.
My deeply ingrained interest in naturalsciences was clearly influenced with my father. My favorite way of thinking about natural science, which I adopted during my highschool years, is to create an active physicalimage in my mind without using mathematical calculations.
My true academic activities began when
I joined the Tokyo University Physics Department. This was during Japan’s war years, andmy studies of “microwaves” under Professor
Kumagai were affected by wartime technology. However, these studies remained withme for a long time, changing shape, andeventually expanding into the study of “lightwaves”, which became the seeds for my firstvisions of semiconductor lasers.
A coincidental meeting with Dr. J. K. Galt
was the most important link between mybackground in microwaves and his idea on
semiconductor lasers.

Fig. 1:20

My interest in “electronics” beganaround the same time as my research in microwaves, when I used electronic systems
such as vacuum tube amplifiers and primitive
computers. An equal interest in “microwavelight waves” and “electronics” led me to theidea of “Photo-Electronic Integration” later in
my life, which will be described as my “dreamfor the 21st century” in the last part of thispaper.

1. Visualizing physical concepts

As I described in the abstract, I wanted tovisualize the law of physics working independently in my mind.
Suppose a piece of heavy stone is sitting on a flat ice plain. If the stone started tomove in one direction, it will keep sliding on
the ice indefinitely in the same direction. If I
want to change the direction of the stone’s
movement, a force is needed (Figure 1). Thisis a “Law of Mechanics”.
“Microwave” was my focus of interest for
many years. Microwaves are electro magnetic waves with very short wavelengths. Here I
focus the electromagnetic wave of about one
centimeter used for radar application (Fig.2).
US bombers used microwave-based radars
during the war. Wavelength measurement ofbombers was my firstjob during my wartime
research.
After the end of thewar, I joined a laboratory of Tokyo University. There was almost
no budget for research.
flat ice
Somehow we obtained
a small microwave tube,
which was used by theForce
Velocity
heavy weight
US bombers, in downtown Tokyo (at the famous Kanda black market).
In the laboratory weconducted various experiment using this tube,
An example visualizing laws of physics. This is a law of Mechanics.
and learned about the

JSAP International No.7 (January 2003)

characteristics of microwaves. Using a handmade grating (parallel wires), we were able
to measure the electric field direction (Fig.3).
And using a metal plate, we could also determine the magnetic field direction. We
discussed our findings with colleagues, andobtained a pretty good “visual image” of microwaves.
Because the basic laws of physics are unchanging, the microwave image was useful indesigning the cavity for a high power radio
frequency oscillator that was used in a cyclotron for nuclear particle experiments. Years
later, this image was also useful in understanding the characteristics of light waves insemiconductor lasers.

2. Experience in the UnitedStates— Room Temperature Operation of Semiconductor Lasers —After nearly 20 years working with Tokyo
University, I decided to go to the U.S. to study
electronics technology and to gain experiencein laboratory work over there, knowing thatsignificant advances in electronics must havemade during the war.
I spent the first year at MIT and the next
year at Bell Telephone Laboratories (BTL).
During my first few years at BTL, I studied nuclear particle radiation detectors for satellite
experiments under Dr. W. L. Brown, a department head.
Three years was the limit for overseas
studies set by Tokyo University. Dr. Brown
kindly introduced me to a few laboratories tosee if there was a place for me in BTL. After
visiting several facilities, I finally met Dr. J. K.
Galt, a laboratory head in the solid state electronics research division. Coincidentally, he
was looking for an experienced physicist to
work with semiconductor lasers. This cameas a most unexpected surprise for me.
Dr. John K. Galt had an idea that “if continuous operation of a semiconductor laser isachieved at room temperature, it will have amajor impact on communication technology”.
I was surprised and at the same timevery much delighted. I immediately resigned

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Electro Magnetic Wave of different wave lengthfrom Tokyo University and joined Dr. Galt’s
group in BTL. I started working with Dr. M.
B. Panish, who was a chemist in the group. I
conducted measurements, and he handled
crystal growth for semiconductor lasers using
GaAs. However, we did not have any idea of
how to proceed with studies targeting room
temperature lasers.
At the Semiconductor laser Conference(1967), fellows from IBM presented a study
on visible lasers using AlGaAs grown on
GaAs. Dr. Panish started immediately to growthe new material and I began studying its luminescence.
Surprisingly, a very strong luminescenceof GaAs was found underneath a thin ALGaAs layer. This was a great discovery. Instinctively I felt that this phenomenon might
be useful in the room temperature operation of semiconductor lasers. The interface
between GaAs and AlGaAs must be ideallyclean! (ref 1)
We started to put an AlGaAs on a GaAs
active layer, using the old growth technique(tipping Fig.2 in ref 1). The lasing thresholdcame down almost one tenth of the previous
value. This is called a Single Hetero Structure(SH). But this threshold was not low enoughto achieve room temperature operation (Fig.4
in ref 1). We started to install another AlGaAs layer on the other side of the active
GaAs layer, called a Double Hetero Structure(DH)(Fig.5) (ref 1).
A great deal of effort went into this DH
growth. Panish, with his assistant S. Sumsky, had to prepare a new type of growthg·Matechnique, call the “sliding boat structure”(Fig.4)(ref 1). It required many delicate adjustments, and improvements were graduallyachieved. My assistant P. Foy made laser devices from this wafer for laser threshold current measurement (Fig.5).
One and a half years later, he found apretty good wafer. We came to the laboratory even on “holiday mornings.”
We finally achieved “Continuous wave
operation (cw)”! This was a big event at BTL.
Many people came to see us. The Vice Presi-

dent of Bell came in the next day.

3. Back to Japan— Challenge for practical usage —I came back to Japan the next fall, in
1971. This time I chose a private company,
Nippon Electric Co. Ltd. (NEC), as the working place for developing applications. I was aleader, and conducted no research by myself.
A very short laser lifetime, and several
other problems were awaiting us. In addition
to the large amount of work required, some���������

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(a)(b)
Fig. 4: (a) A new ”moving seed“ multiple layer solution growth apparatus (Dec. 25, 1969). With thisapparatus three DH epitaxial layers can be grown in succession from three solutions. A slider will be
moved (push-pull) from outside. All parts are graphite. (b) A photograph of an early sliding boat. The
top and the bottom part inserts were tied by platinum wires.

JSAP International No.7 (January 2003)

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Fig. 5: The DH laser threshold current density Jth as a function of the active layer thickness d. The linear relation demonstrates an ideal DH function, the sublinear dependence at small d is due to the lossof optical confinement. (ref 1)technical breakthroughs were also necessary
before we could achieve practical applications.
In the beginning, the lifetime of the lasers was about one minute. We conductedmany trials, changing impurities, dopings,
contaminations, and other factors, but withno major effect.
This was a very difficult time for me, notknowing why we were making so little progress. I just kept telling myself, “We should be
able to achieve a long life laser.”A breakthrough occurred in 1973, whena young colleague, H. Yonezu, found “darklines” in a degraded laser (Fig.6). These lines
appeared in a small laser structure. Degradation is always associated with narrow darklines, which run along a certain crystalline orientation. Dark lines grow from dark spots,
which are caused by dislocations in the crystal. We used better substrate crystals andimproved growth techniques, and as a result
the lifetime increased gradually, from minutes
to hours and days.
At the Conference on Laser Engineeringand Application (1973), I announced a record
laser life that had exceeded the 2000-hourmark by a few hundred hours. At the conference, I met a researcher from BTL. had alsoachieved a record life of about 2000 hours.
This was an astounding revelation (ref 1).
The same progress had occurred at the sametime in two places across the Pacific, independently!
“Competition and Collaboration”
While I was in NEC, I made many friends
in other companies. At meetings I was ob-

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serving their activities, and noticed that discussions were not as productive as they could
have been. I suggested that we should discuss basic issues, even among researchers at
rival organizations.
A “Semiconductor laser family” has arisen in this field, made up of a group of people
who have developed many of application systems during 1980s. They get together every
fall and spring, around the times when Applied Physics meetings are held.

4. Dream in the 21st century

In large scale Si LSIs (finer pattern size,
DR < 0.1 µm) and higher operating speeds (f> GHz), an interconnection crisis occurs dueto the increased resistance of metal wirings.
Results of calculations are shown in Fig 7(Fig.2 in ref 2). Optical interconnections decrease the delay effectively for long connections over 10 µm.
A large numberof optical interconnections (103 – 104)
will be required for
the ULSI system.
Small size and low
HOLDER
power of semiconductor lasers is es[100]sential. A µm size
surface emitting(001)
laser with µ-watt
100 µpower has already
STRIPECONTACTbeen reported (P.
CLEAVED FACE
D. Dapkas, ref. 9
Fig. 6: “Dark-line“ defect pattern in a degraded DH laser e. Ij pattern was taken
in ref 2). Furtherwith an SEM. The stripe contact is removed after aging. (H.Yonezu et al.: A.P.L, Jan.
1974)
more, the cost of
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these lasers must be much lower than thoseavailable today.
In the abstract, I described my interestin both “Electronics” and “Microwave →Light” in the early stages of my research. Later, this led me to the idea of Photo-Electronicintegration as a dream for the 21st century.
Many problems related to devices, processes, and system structures must be solved
to make this system valuable for practical usage.
Process compatibility must be achieved.
High temperature ranges in the Si process
must be clearly delineated from low temperature zones of III-Vs and metal wire evaporation.
Several studies are being done to overcome the problem of lattice mismatches between Si and (III-V)s. H. Yonezu and others
achieved dislocation-free GaAs on Si throughthe skillful use of interface layers (ref. 4). M.
Tamura showed that a remarkable decreaseof dislocation in GaAs could achieved by annealing (Fig. 8 in ref 2).
An important message that must be reported relates to the study of optical interconnection, which was conducted by a group ofpeople carefully selected from different specialties between 1990 and 1994 (the U-OEIC
study group). The report was very insightful,and is still valuable today (ref. 3). An example of optical interconnection is the structure
shown in Fig.8 (ref.2), where an optical plateis separated from an LSI substrate. Opticalpaths can be installed freely from LSI circuits.
It will take time to achieve practical applications using these photo-electronic integrated system. A variety of new techniques must
be developed to complete the system, andthis will require the collaborative effort of en-

gineers from different fields of specialization.
But when this goal is finally realized, the system will be of great benefit for society in 21st
century.

still meets every year. This is the best time forme to reflect on my many years of research activity.
Finally, I would like to say that it is a greathonor to have my lifetime research activities
recognized by the very prestigious “Kyoto
Prize.” I would like to thank all the people
supported me during this 50 years of study.
Thank you very much.

Summary
Looking back, my meetings with significant people defined milestones of my life longcareer.
Hiroo Kumagai was my life-long teacher.
He introduced me not only to techniques suchas those related to microwaves, but also provided me with my physics background in thelaboratory.
John Galt provided me with the theme ofsemiconductor lasers. This has become a central part of my career in photo-electronics integration.
I also learned from many colleagues about
important techniques for practical applications.
I am an ordinary researcher, not a great
inventor or a scholar. However, I have always
enjoyed the highest level of collaboration, because I have tried to give of myself without
asking much in return.
Even so, I have reaped many great rewards, not only in terms of physical gain, butalso in the human relationships with the people
with whom I have collaborated. The “semiconductor laser family” described in section 3

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Acknowledgements• Teachers and friends at Gakushuin High School• Supporters and friends at Kumagai Laboratory• Supporters and friends at Science and Engineering Institute and the Institute for Nuclear Studyof the University of Tokyo• Supporters and friends at the Nuclear Science
Laboratory, Massachusetts Institute of Technology• Bell Laboratories
Dr. J. K. Galt (department chief) and Dr. W. L.
Brown (section chief) of the Basic Research Department
Supporters and friends at the Basic Research
Department and the Research and Development
Department• Supporters and friends at the Central ResearchLaboratories and other NEC laboratories involved in semiconductor and opto electronic research• Supporters, friends, at the “Semiconductor Laser Friends” at NEC, Hitachi, Mitsubishi, Fujitsu,
Toshiba and Matsushita

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10-11
11 ) Izuo HAYASHI: IEEE Transactions on Electron
Devices ED31, 1630 (1984).
2 ) Izuo HAYASHI: OYO BUTURI 65, 824(1996). (inJapanese)3 ) Masataka HIROSE and 15 members: U-OEIC Research Study 1992-1995 in Japanese (Optoelectronic Industry and Technology Development
Association, 1-20-10 Sekiguchi, Bunkyo-ku, Tokyo 112-0014, Phone: +81-3-5225-6431).
4 ) K. MOMOSE and H. YONEZU et al.: J.of Appl.
Phys. 79, 4151(2001).

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• Supporters and friends at the Optoelectronics
Joint Research Laboratories, and at the Ministryof Trade and Industry project• Supporters and friends at the Optoelectronics
Technology Research Laboratory• Supporters at the U-OEIC Study Group (Optoelectronic Integration System), Optoelectronic
Industry and Technology Development Association• The Japan Society of Applied Physics• The Engineering Academy of Japan• The Japan Physical Society• IEEEAnd many others who have supported me.
M. B. Panich, H. C. Casey, A. Y. Cho, C. T. Hwang,
J. Dyment, J. W. Goodman, Shigeki Suwa, Seishi
Kikuchi, Yukimatsu Takeda, Michiharu Nakamura,
Minoru Oda, Yoshibumi Katayama, Masataka Hirose, Ryoichi Ito, Jumpei Tsujiuchi, Hiroo Yonezu, Yasuo Nannichi, Koro Kobayashi, and Hirofumi Rangu,
and many other individuals.

LD

Amp

PD

PD

LD:Laser Diode
PD:Photo detector
Te = Delay time of LD, PD andassociated circuits (driver and amp)

Fig. 7: Signal Delay of Optical versus Electrical Interconnections
on the microprocessor. Optical interconnection delay includes
electrical circuits delay Te=100ps in addition to that of the light.
(A. Iwata)

Optical Plate
IC Chip
MCM Substrate

Fig. 8: Optical interconnection circuits can be installed freely
from LSI circuits in MCM substrate.

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