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Prof. John A. Copeland ECE Georgia Tech

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 ECE Georgia Tech

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  1. LSA Diodes(breaking the 1/f2 power law for semiconductor electronic devices)in Honor ofProf. Lester F. EastmanCornell University Prof. John A. Copeland ECE Georgia Tech

  2. 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.

  3. n-GaAs Oscillator Time Line 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

  4. velocity dE dV E < 3000 v/cm: E > 3000 v/cm: dE dV Mobility = dV/dE Carrier drift velocity (107 cm/s) 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.

  5. v=107 cm/s f = v/L n-GaAs Diode from ingot 10-micron epitaxial layer

  6. 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)

  7. Modes of Operation Frequency x Length (cm/s) Carrier Density x Length

  8. Gunn Diode P=a/f2 • Kennedy and Eastman • 350 W @ 8 GHz

  9. Handheld LSA mm-wave Doppler Radar Profilometer Audio Headset 3v R RF LSA diode in waveguide to antenna.

  10. 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.

  11. 1980 Experience working with GaAs, and later mixed 3-5 compounds (e.g., GaxAl1-xAsyP1-y), led to LEDs and lasers for lightwave systems.

  12. 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/

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