LSA Diodes (breaking the 1/f 2 power law for semiconductor electronic devices) in Honor of Prof....
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Transcript of LSA Diodes (breaking the 1/f 2 power law for semiconductor electronic devices) in Honor of Prof....
LSA Diodes(breaking the 1/f2 power law for
semiconductor electronic devices)
in Honor of
Prof. Lester F. EastmanCornell University
Prof. John A. CopelandECE
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 traveling-wave 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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1957 Eastman - receives Ph.D., joins Cornell faculty. 1961 Ridley and Watson's paper on negative resistance in solids
1962 C. Hilsum's paper on transferred-electron amplifier, oscillators
1963 J.B Gunn (IBM) shows moving electric-field in n-GaAs 1964 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
n-GaAs Oscillator Time Line
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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.
E < 3000 v/cm:
E > 3000 v/cm:
dEdV
dEdV
velocity
Electric Field (kV/cm)
Carrierdrift velocity(107 cm/s)
Mobility = dV/dE
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n-GaAs Diode from ingot 10-micron epitaxial layer
v=107 cm/s
f = v/L
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)
Carrier Density x Length
Fre
quen
cy x
Len
gth
(cm
/s)
Modes of Operation
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- Kennedy and Eastman 350 W @ 8 GHz
Gunn DiodeP=a/f2
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Handheld LSA mm-wave Doppler Radar
Profilometer
LSA diode in waveguideto antenna.
Audio Headset
3v R
RF
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 mm-wave 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.
Experience working with GaAs, and later mixed 3-5 compounds (e.g., GaxAl1-xAsyP1-y), led to LEDs and lasers
for lightwave systems.
1980
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: [email protected]
Alternate URL: users.ece.gatech.edu/copeland/jac/LSA/