1. We ignore here the developments in high-speed transistors. For example, Rodwell, M, Lee, Q., Mensa, D., Guthrie, J., Martin, S.C., Smith, R.P., Pullela, R., Agarwal, B., Jaganathan, S., Mathew, T., and Long, S, (1999) Transferredsubstrate HBT integrated circuits, Solid-State Electr.
43, 1489–1495.
2. Quantum cascade lasers: Tredicucci, A., Gmachl, C., Capasso, F., Sivco, D.L., Hutchinson, A.L., and Cho, A.Y. (1999) Long wavelength superlattice quantum cascade lasers at lambda approximately= 17 μm, Appl. Phys. Lett., 74, 638–640; Capasso, F., Gmachi, C., Kohler, R., Paiella, R., Tredicucci, A., Hutchinson, A.L., Sivco, D.L., Baillargeon, J.N., Cho, A.Y., and Liu, H.C., (2000) High performance quantum cascade lasers for the lambda =4 to 17 μn region and their chemical sensing applications in Conference Proceedings. 2000 International Conference on Indium Phosphide and Related Materials, IEEE, Piscataway, NJ, USA, pp.262-265. Photo-mixer: Verghese, S., Mclntosh, K.A., and Brown, E.R. (1997) Optical and terahertz power limits in the low-temperature-grown GaAs photomixers, Appl. Phys. Lett., 2743-2745. Harmonic generation: T. Crowe, this volume. Resonant tunneling diodes (RTD’s): Brown, E.R., Soderstrom, J.R., Parker, C.D., Mahoney, L.J., Molvar, K.M., and McGill, T.C. (1991) Oscillations up to 712 GHz in InAs/AlSb resonant-tunneling diodes, Appl. Phys. Lett., 58, 2291-2293. RTD arrays: Reddy, M.; Martin, S.C.; Molnar, A.C.; Muller, R.E.; Smith, R.P.; Siegel, P.H.; Mondry, M.J., Rodwell, M.J.W., Kroemer, H., and Allen, S.J., Jr. (1997) Monolithic Schottky-collector resonant tunnel diode oscillator arrays to 650 GHz, IEEE Electr. Dev. Lett.
18, 218-221. Superlattice electron device (SLED): Schomburg, E., Scheuerer, R., Brandi, S., Renk, K.F., Pavel’ev, D.G., Koschurinov, Yu., Ustinov, V., Zhukov, A., Kovsh, A., Kop’ev, P.S. (1999) InGaAs/InAlAs superlattice oscillator at 147 GHz, Electr. Lett.
35, 1491-1492.
3. Gronqvist, H., Kollberg, E.,and Rydberg, A. (1991) Quantum-well and quantumbarrier diodes for generating submillimeter wave power, Micro. and Opt. Tech. Lett.
4, 33–38.
4. Tucker, J.R. (1979) Quantum limited detection in tunnel junction mixers. IEEE J. Quant. Electr.
QE-15, 1234–1258.
5. Ktitorov, S.A., Simin, G.S., and Sindalovski, V.Y. (1971) Bragg reflections and the high-frequency conductivity of an electronic solid-state plasma, Fizika Tverdogo Tela
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