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: jcopeland@ece.gatech.edu

Alternate URL: users.ece.gatech.edu/copeland/jac/LSA/