Spontaneous dc Current Generation in a Resistively Shunted Semiconductor Superlattice Driven by a Terahertz Field

Abstract

We study a resistively shunted semiconductor superlattice subject to a high-frequency electric field. Using a balance equation approach that incorporates the influence of the electric circuit, we determine numerically a range of amplitude and frequency of the ac field for which a dc bias and current are generated spontaneously and show that this region is likely accessible to current experiments. Our simulations reveal that the Bloch frequency corresponding to the spontaneous dc bias is approximately an integer multiple of the ac field frequency. [S0031-9007(98)05660-9] PACS numbers: 72.20.Ht, 05.45. + b, 73.20.Dx In 1928 Bloch demonstrated [1] that electrons in a periodic lattice potential with period a subject to a dc electric field E dc undergo oscillations with characteristic frequency v B eaE dc ͞h. In naturally occurring solids, observations of Bloch oscillations are precluded by the need for very high applied electric fields to reduce the Bloch oscillation period below the dephasing times arising from the ever-present scattering due to impurities and phonons. In 1970, Esaki and Tsu [2] recognized that due to their longer spatial periods, semiconductor superlattices (SSLs) can support Bloch oscillations in the terahertz (THz) domain-comparable to or faster than the corresponding scattering frequencies-even for modest field strengths (ϳ1 kV͞cm). Thus, not only should the Bloch oscillations be observable in SSLs, but SSLs could also serve as devices to produce THz radiation [2]. When, in addition to the static field E dc , an SSL is subjected to an ac field of frequency V, the static current-voltage characteristic can exhibit structures at v B nV (where n is an integer) [3,4]. In the presence of dissipation, multiphoton transitions involving different n can lead to a Bloch oscillator capable of producing radiation from almost zero to the THz frequencies. Recently, experiments involving novel electromagnetic radiation sources and coupling techniques have revealed additional effects of THz radiation fields on the dc conductivity of an SSL [5-8], including (i) THz multiphoton-assisted tunneling [5], (ii) ac-field-induced reduction of the dc current [6], (iii) absolute negative conductance [7], and (iv) resonant changes in conductivity [8].In the present Letter, we examine a question that is roughly the converse of the Bloch oscillations in an SSL: namely, can a purely ac external field applied to an appropriately configured (but unbiased) SSL create a dc bias and corresponding dc current? In technical terms, this corresponds to a spontaneous breaking of spatial reflection symmetry. Using the methods of nonlinear dynamics, we show that the answer to this question is "yes" and find the condition for spontaneous dc current generation in the circuit consisting of the SSL shunted by an external resistance. We observe that the Bloch frequency corresponding to the spontaneously generated bias across the SSL is approximately an integer multiple of the frequency of the external ac field and explain the origin of this...

Symmetry breaking in a driven and strongly damped pendulum

“…These results can be directly applied to the studies of novel mechanism of THz radiation rectification in semiconductor superlattices [25] because this system has underlying pendulum dynamics [26,30]. Note that in some cases pendulum-like equation of the third order [32,33] and a pendulum equation with a nonlinear damping term supporting symmetry of the problem [34] naturally arise in different models of semiconductor superlattices.…”

“…However, it has been shown recently that another type of solid state microstructures -semiconductor superlattices subjected to a high-frequency electric field -can demonstrate very rich nonlinear dynamics similar to dynamics of the Josephson junctions [21,22,23,24,25,26,27]. In particular, an analog of inverse ac Josephson effect has been predicted for the superlattices [23,25].…”

“…In particular, an analog of inverse ac Josephson effect has been predicted for the superlattices [23,25]. Moreover, within some reasonable approximations nonlinear dynamics of an ac-driven semiconductor superlattice in the miniband transport regime is governed by a periodically forced and damped pendulum [26,27].…”

Rectification of terahertz radiation in semiconductor superlattices in the absence of domains

“…If the governing equations remain invariant in transformation S, we say that they are symmetric or have symmetry S. In our previous works we have focused on the appearance of a spontaneous dc voltage via dynamical symmetry breaking [21,18,29,40,28]. Let u 0 be the generated dc voltage:…”

Current responsivity of semiconductor superlattice THz-photon detectors

“…19 Several recent papers show that the curious behavior of electrons in the superlattices may give rise to a rich variety of new nonlinear phenomena occurring in the THz-field irradiated superlattices. [20][21][22][23][24][25] In a number of papers Esaki-Tsu negative differential conductance was found to be experimentally realizable 26,27 and has been carefully examined [28][29][30] in the context of development of new millimeter-wave band ͑0.03-0.3 THz͒ oscillators. On the other hand, the recent observations of a strong dc current suppression indicating dynamical localization of electrons, 31 absolute negative conductance, 32,33 and Shapiro steps on the dc current-voltage curve of the THzfield irradiated superlattices 34 open the prospects for applications of the superlattices as novel solid state detectors operating in 1-10 THz-frequency band which the Bloch frequency in the superlattices normally belongs to.…”