Abstract:
The theory of the interaction of a monoenergetic flow of injected electrons with a strong high-frequency ac electric field in resonant-tunneling diode (RTD) structures with asymmetric barriers of finite height and width is generalized. In the quasi-classical approximation, electron wavefunctions and tunneling functions in the quantum well and barriers are found. Analytical expressions for polarization currents in RTDs are derived in both the general case and in a number of limiting cases. It is shown that the polarization currents and radiation power in RTDs with asymmetric barriers strongly depend on the ratio of the probabilities of electron tunneling through the emitter and collector barriers. In the quantum mode, when $\delta=\varepsilon-\varepsilon_r=\hbar\omega\gg\Gamma$ ($\varepsilon$ is the energy of electrons injected in the RTD, $\hbar$ is Planck’s constant, $\omega$ is the ac field frequency, $\varepsilon_r$ and $\Gamma$ are the energy and width of the resonance level, respectively), the active polarization current in a field of $E\approx 2.8\hbar\omega/ea$ ($e$ is the electron charge and $a$ is the quantum-well width) reaches a maximum equal in magnitude to 84% of the direct resonant current, if the probability of electron tunneling through the emitter barrier is much higher than that through the collector barrier. The radiation-generation power at frequencies of $\omega$ = 10$^{12}$–10$^{13}$ s$^{-1}$ can reach 10$^5$–10$^6$ W/cm$^2$ in this case.
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