LSA Diodes
(breaking the 1/f2 power law for
semiconductor electronic devices)
in Honor of
Prof. Lester F. Eastman
Cornell University
Prof. John A. Copeland
ECE
Georgia Tech
The LSA Era:1964-69
Transistors started to replace Vacuum
Tubes in audio, then RF applications.
Long distance (intercity) telephone
voice traffic and network TV, carried
by microwave radio relay towers.
Microwave circuits required travelingwave and close-spaced vacuum
tubes, expensive and unreliable.
Viet Nam War (radar uses magnetron
tubes for high pulse power).
Needed: microwave semiconductor
devices.
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n-GaAs Oscillator Time Line
1957
1961
1962
1963
1964
Eastman - receives Ph.D., joins Cornell faculty.
Ridley and Watson's paper on negative resistance in solids
C. Hilsum's paper on transferred-electron amplifier, oscillators
J.B Gunn (IBM) shows moving electric-field in n-GaAs
Eastman starts research on compound semiconductors
(GaAs, Gunn-effect, high power pulses for radar)
1965 Copeland - receives Ph.D., joins Bell Labs in Murray Hill, NJ
(GaAs, Gunn-effect, continuous power for communications)
1966 McCumber & Chenoweth's computer simulation of Gunn osc.
1967 Copeland - computer simulations show a resonant circuit
can cause a n-GaAs diode to oscillate (LSA mode) at much higher
frequency with similar power - theory says n/f critical, not length.
1967 Eastman and Copeland travel to conference in Bad
Neuheim, and visit Munich, London, Royal Radar Establishment
1967 Copeland - produced 20 mW continuous at 88 GHz.
1967 Keith Kennedy and Eastman produced high power pulses
with LSA Oscillators (350 watts at 8 GHz).
1970 Copeland receives IEEE Morris Liebmann Award for LSA
velocity
E < 3000 v/cm:
dE
dV
E > 3000 v/cm:
dE
dV
Mobility = dV/dE
Carrier
drift
velocity
(107 cm/s)
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Electric Field (kV/cm)
Electron drift velocity vs. electric field in n-type GaAs.
The ac (differential) resistance is negative for E > 3000 v/cm
Why? Brian Ridley may explain in a few minutes.
v=107 cm/s
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f = v/L
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n-GaAs Diode from ingot
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10-micron epitaxial layer
For LSA (Limited Space
Charge) operation, the
electric field must dip
for a portion of each
cycle into the positive
mobility region, to
quench any space
charge that has begun
to accumulate.
from "Gunn-Effect Devices",
B.G.Bosch and R. W.
Engelmann, John Wiley
&Sons, NY (c. 1970)
Frequency x Length (cm/s)
Modes of Operation
Carrier Density x Length
Gunn Diode
P=a/f2
- Kennedy and Eastman
350 W @ 8 GHz
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QuickTime™ and a
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QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
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Handheld LSA mm-wave Doppler Radar
Profilometer
Audio Headset
3v
R
RF
LSA diode in
waveguide
to antenna.
1968 to 2008 - Where did the research lead?
At Cornell: more coming later in this program.
At Bell Labs:
1968 - Because of the possibility of having mmwave semiconductor devices, development of a
guided millimeter-wave system began.
1971 - Corning gave Bell Labs a piece of optical
fiber to analyze, and the guided mm-wave system
development was stopped before going into
manufacture. Device research turned to GaAs
lasers, and long-wavelength lasers and
photodetectors for 1.3 to 1.5 micron wavelengths.
1980
Experience working with GaAs, and later mixed 3-5
compounds (e.g., GaxAl1-xAsyP1-y), led to LEDs and lasers
for lightwave systems.
References to my papers, which have references to
the work of many others who contributed to this field.
www.csc.gatech.edu/copeland/
These slides, old Spectrum and Electronics articles
www.csc.gatech.edu/copeland/jac/LSA/
Email: jcopeland@ece.gatech.edu
Alternate URL: users.ece.gatech.edu/copeland/jac/LSA/