ISSN 1063-7842, Technical Physics, 2011, Vol. 56, No. 6, pp. 826–830. © Pleiades Publishing, Ltd., 2011. Original Russian Text © G.K. Rasulova, P.N. Brunkov, I.V. Pentin, V.V. Kovalyuk, K.N. Gorshkov, A.Yu. Kazakov, S.Yu. Ivanov, A.Yu. Egorov, D.A. Sakseev, S.G. Konnikov, 2011, published in Zhurnal Tekhnicheskoі Fiziki, 2011, Vol. 81, No. 6, pp. 80–84. 826 Weakly coupled semiconductor superlattices attract attention of researchers due to their ability to generate stable current oscillations in the rf range from 100 kHz to 10 MHz [1–7]. Generation of current oscillations in weakly coupled superlattices (SLs) was predicted theoretically in 1994 [1] and then observed experimentally in 1995 [2, 3]. Self-sustained current oscillations in weakly coupled SLs appear at a constant voltage applied in the negative differential conductiv- ity (NDC) region of the current–voltage characteris- tic. It was shown that generation of current oscillations is associated with space–time oscillations of the elec- tric domain wall [1, 4]. The frequency of self-sustained oscillations depends on technological parameters of the superlattice structure, such as the doping level of quantum wells and the size of quantum wells and bar- riers. In our experiments, we detected generation of self- sustained oscillations of current in a GaAs/Al 0.3 Ga 0.7 As (28/10 nm) 30-period semiconductor superlattice [5, 6]. Qualitative analysis of the mechanism of generation of self-sustained oscillations in weakly coupled superlat- tices, which is associated with periodic expansion and contraction of the electric domain wall, has shown [7] that the generation of current oscillations must be accompanied with optical radiation in the far infrared spectral range. We believe that the frequency of current oscillations is determined by the residence time of trapped electrons in quantum wells (QWs) forming an extended boundary of an electric-field domain, which in turn is determined by the time of the Coulomb interaction between electrons trapped in a QW and electrons entering the QW. An extended domain wall is a system of coupled oscillators, each of which is a one-barrier tunnel diode consisting of two neighboring QWs separated by a bar- rier [7]. Inverse population of size-quantization levels is produced at the instant of domain wall expansion in the case of mismatch of miniband energy levels in the QW forming the domain wall and is due to electron trapping in QWs and their capture in the region of extended domain walls during the time equal to the period of current oscillations. Depletion of size-quan- tization levels takes place upon contraction of the domain wall (i.e., upon resonant equalization of energy levels of minibands in the QWs forming the domain wall). Thus, optical radiation must be modu- lated by the frequency of natural current oscillations in the superlattice. The wavelength of IR radiation is determined by the energy of intersubband transitions whose resonant matching ensures electron tunneling along the superlattice axis. Since the radiation power of a single structure is low and amounts to tens of nanowatts, several struc- tures (each of which is an individual self-sustained oscillator) should be combined into one. Thus, we must obtain generation of current oscillations in two or more coupled mesostructures for a single fixed con- stant voltage. This study aims at analysis of mutual fre- quency locking to two generators of self-sustained cur- rent oscillations based on a weakly coupled superlattice. The structures under investigation were grown by molecular-beam epitaxy (MBE) on an n + -GaAs substrate and had the form of a GaAs/Al 0.3 Ga 0.7 As (28/10 nm) superlattice consisting of 30 periodically alternating layers of GaAs (28 nm) quantum wells and Mutual Synchronization of Two Coupled Self-Oscillators Based on GaAs/AlGaAs Superlattices G. K. Rasulova a *, P. N. Brunkov b , I. V. Pentin c , V. V. Kovalyuk c , K. N. Gorshkov c , A. Yu. Kazakov c , S. Yu. Ivanov a , A. Yu. Egorov d , D. A. Sakseev b , and S. G. Konnikov b a Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia e-mail: rasulova@sci.lebedev.ru b Ioffe Physical Technical Institute, Russian Academy of Sciences, ul. Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia c Moscow Pedagogical University, M. Sukharevskii per. 6, Moscow, 119345 Russia d St. Petersburg Research and Education Center of Science and Technology, Russian Academy of Sciences, St. Petersburg, 195220 Russia Received December 2, 2010 Abstract—The interaction of self-oscillators based of 30-period weakly coupled GaAs/AlGaAs superlattices is studied. The action of one self-oscillator on the other was observed for a constant bias voltage in the absence of generation of self-sustained oscillations in one of the oscillators. It is shown that induced oscillations in the locking oscillators appear due to excitation of oscillations in the system of coupled oscillators forming the electric-field domain wall at the frequency of one of the higher harmonics of a forcing oscillation. DOI: 10.1134/S1063784211060211 SOLID STATE ELECTRONICS