Superlattice space-charge-wave analyses in a modified drift-diffusion model and in a simplified balance-equation formulation |
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Authors: | XL Lei NJM Horing H L Cui KK Thornber |
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Institution: | 15. China Center of Advanced Science and Technology (World Laboratory), P.O. Box 8730, Beijing, 100080, People’s Republic of China 25. State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Metallurgy Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, People’s Republic of China 35. Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ, 07030, USA 45. NEC Research Institute, 4 Independence Way, Princeton, NJ, 08540, USA
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Abstract: | Unstable space-charge-waves in superlattice miniband transport are investigated using a modified drift-diffusion model and using a simplified one-dimensional hydrodynamic balance-equation formulation with a relaxation-time approximation. We point out that the earlier widely accepted notion, that in the small wavevector limit the space-chargewave (SCW) propagates at a phase velocity equal to the carrier drift velocity and with an amplitude-growth rate equal to the negative value of the mobility frequency, -ω c, was crucially based on the implicit assumption that the system momentum relaxation time τm is extremely small. Taking account of a finite momentum relaxation time, we find that even the drift-diffusion model would yield results significantly different from the above predictions: the phase velocity of a long-wavelength traveling SCW can be much slower than the carrier drift velocity and its amplitude-growth rate much smaller than -ωc. A hydrodynamic balance-equation formulation, which properly treats energy dissipation and further reduces the amplitude-growth rate, provides a convenient tool for improved qualitative analyses in SCW-related problem in semiconductor superlattices. |
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