Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Patent
1995-11-02
1997-02-25
Mintel, William
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
257 21, 257 22, 257 25, 257 97, H01L 2906, H01L 310328, H01L 310336
Patent
active
056061757
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS
This document corresponds to International PCT Application PCT/GB94/00406.
The present invention relates to a quantum well device capable of operating over a range of frequencies including those corresponding to micrometer waves. For instance the device can be used to emit, amplify, modulate, detect and frequency multiply or divide micrometer radiation.
Micrometer radiation is electromagnetic radiation of wavelengths failing between infrared and millimeter wave radiation. Known sources of micrometer radiation include high temperature radiators, electron synchrotrons, backward wave oscillators and gas lasers. All of these known devices are inefficient and have low power densities and most of them are disadvantageously large and complex.
Gas lasers may be used to amplify micrometer radiation but are large, expensive and impractical for many applications. There are no other devices available for amplifying micrometer radiation.
Frequency multiplication of micrometer radiation can be carried out using Josephson junctions or non-linear dielectric materials but these known methods are inefficient.
There are a number of widely used solid state devices which operate at microwave frequencies, such as double barrier resonant tunnelling diodes, Gunn diodes and tunnel diodes, but none of these is capable of operating at micrometer wave frequencies. The high frequency working limit of such devices is limited by the properties of the materials used to fabricate the devices. Materials, i.e. semiconductors, are constantly being improved to extend this limit but it is generally accepted that existing solid state devices cannot be made to work at frequencies associated with micrometer radiation.
There are a number of important current, and potential, uses of micrometer radiation including: scientific research, particularly in the area of remote sensing and radio astronomy; instrumentation, including gas analysis; metrology, especially of voltage through the Josephson effect, of distance and of very short times; communications, including deep space communications and secure links; and radar systems, particularly with ultra compact antennas.
An object of the present invention is to provide a device which can operate at micrometer wavelengths and which obviates or mitigates the disadvantages of the known devices discussed above.
According to the present invention there is provided a quantum well device having an active region adapted in use to pass a tunnelling current of charge carriers, the active region comprising layers of material forming alternating potential barriers and potential wells arranged so as to define a first potential well at one end of the active region having regard to the direction of flow of the tunnelling current of charge carriers and a further structure, said first potential well defining a first quasi-defined energy level and the further structure defining second and third quasi-defined energy levels, the relative heights and thicknesses of the potential barriers when the device is in use being structured so that the first quasi-defined energy level has a longer lifetime than the second and third quasi-defined energy levels and there is a degree of coupling between the three quasi-defined energy levels which is strongest between the second and third quasi-defined energy levels, the arrangement being such that the transmission coefficient through the active region shows a resonance peak at each of the energies of the three quasi-defined energy levels, the transmission peak at the energy of the first quasi-defined energy level being greater than the transmission peaks at the energies of the second and third quasi-defined energy levels respectively, and the structure being such that when the device is in use the energy of the first quasi-defined energy level lies between the energies of the second and third quasi-defined energy levels but is greater or less than the average of the energies of the second and third energy levels.
In use the current of charge carrier
REFERENCES:
patent: 4894526 (1990-01-01), Bethea et al.
patent: 5355000 (1993-02-01), Delacourt et al.
P. C. Harness et al., "Double-Barrier Resonant Tunneling Structures Incorporating Superlattice Energy Filters", Journal of Applied Physics, vol. 71, No. 6, American Institute of Physics, 15 Mar. 1992, pp. 3019-3024.
M. Buttiker et al., "Traversal Time for Tunneling", Physical Review Letters, vol. 49, No. 23, The American Physical Society, 6 Dec. 1982, pp. 1739-1742.
C. Sirtori et al., "Giant, Triply Resonant, Third-Order Nonlinear Susceptibility .chi.3.sub..omega..sup.(3) in Coupled Quantum Wells", Physical Review Letters, vol. 68, No. 7, The American Physical Society, 17 Feb. 1992, pp. 1010-1013.
K. Husimi et al., "Progress of Theoretical Physics", The Physical Society of Japan, vol. 9, Apr. 1953, pp. 381-402.
Mintel William
The University of Manchester Institute of Science & Technology
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