Frequency limit of double barrier resonant tunneling oscillators

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Abstract
The frequency limit of negative differential resistance (NDR) devices employing resonant tunneling in double barrier quantum well structures is analyzed. We show that the standard theoretical approach to resonant tunneling together with a unitarity bound leads to a lower bound on NDR which is in turn related to the maximum oscillator frequency. The bound on NDR can be achieved in devices with narrow width resonances. However, too narrow a width can cause Wigner–Eisenbud resonance time delay. These considerations indicate that devices of the type studied by T. C. L. G. Sollner, P. E. Tannenwald, D. D. Peck, and W. D. Goodhue [Appl. Phys. Lett. 45, 1319 (1984)] could oscillate up to roughly 1 THz.