Dispersion and instability of drift waves in a fine-layered semiconductor structure
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CONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Dispersion and Instability of Drift Waves in a Fine-Layered Semiconductor Structure A. A. Bulgakov^ and O. V. Shramkova^^ Institute of Radio Physics and Electronics, National Academy of Sciences of Ukraine, Kharkov, 61085 Ukraine ^e-mail: [email protected] ^^e-mail: [email protected] Submitted June 30, 2005; accepted for publication April 22, 2006
Abstract—Drift waves in a fine-layered periodic semiconductor structure subjected to an electric field that induces the drift of charge carriers of different signs are considered. It is shown that the drift waves in this structure can propagate at an angle to the direction of the current, while their properties are governed by the thickness of the layers and the propagation direction. These waves are formed of concentration waves in separate layers and, thus, are “collective” waves. The conditions for origination of instabilities and analytical relations for increments are derived. Origination of instabilities is related to the energy exchange between drift waves in separate layers. PACS numbers: 73.20.Mf DOI: 10.1134/S1063782606120037
1. INTRODUCTION In the second half of the last century, considerable advances were made in mastering a wide range of electromagnetic-wave frequencies for practical applications, and this extended to millimeter wavelengths. However, the submillimeter region of wavelengths (the terahertz region) remained unaffected by these advances. At the same time, the terahertz range can be of interest not only in already-mastered fields but also in quite new fields, for example, medicine and studies of relict radiation in the Universe. The main line in the present-day technology is related to formation of objects with sizes of several micrometers or smaller. Impressive advances in the technology have been attained in the area of formation of nanostructures with sizes of thousandths and hundredths of a micrometer. In this paper, we report the results of a theoretical study of electrodynamic properties of a fine-layered periodic semiconductor structure. In essence, such a structure is a new material that can be obtained by doping the same semiconductor (for example, GaAs). This is a so-called nipi crystal. If the thickness of the layers ranges from 0.1 µm to several micrometers, such a periodic structure represents a uniaxial anisotropic material for the terahertz range of frequencies [1, 2]. Since the thickness of the layers exceeds the mean free path of electrons (or is comparable with this path), the examination is performed using the hydrodynamic theory [3]. This approach makes it possible to derive simple ana-
lytical formulas for the increments of the instability that originates in an external electric field as natural waves propagate at an arbitrary angle relative to the direction of carrier drift. We consider the specific features of twoflux instabilities that were referred to in early publications as drift instability [4], resonance instability (Buneman instability) [5–7], and Bohm–Gross r
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