LSA Diodes (breaking the 1/f 2 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.
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Prof. John A. Copeland
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.
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
E < 3000 v/cm:
E > 3000 v/cm:
Mobility = dV/dE
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.
f = v/L
n-GaAs Diode from ingot 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)
Carrier Density x Length
LSA diode in waveguide
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.
References to my papers, which have references to the work of many others who contributed to this field.
These slides, old Spectrum and Electronics articles
Alternate URL: users.ece.gatech.edu/copeland/jac/LSA/