%% Books @book{fds167377, Author = {Luis Bonilla and Stephen Teitsworth}, Title = {Nonlinear wave methods for electronic transport in condensed matter systems}, Publisher = {Wiley - VCF}, Year = {2010}, Key = {fds167377} } %% Papers Published @article{fds325702, Author = {Ghanta, A and Neu, JC and Teitsworth, S}, Title = {Fluctuation loops in noise-driven linear dynamical systems}, Journal = {Physical review. E}, Volume = {95}, Number = {3}, Year = {2017}, Month = {March}, url = {http://dx.doi.org/10.1103/PhysRevE.95.032128}, Doi = {10.1103/PhysRevE.95.032128}, Key = {fds325702} } @article{fds248435, Author = {Dannenberg, PH and Neu, JC and Teitsworth, SW}, Title = {Steering most probable escape paths by varying relative noise intensities.}, Journal = {Physical Review Letters}, Volume = {113}, Number = {2}, Pages = {020601}, Publisher = {American Physical Society}, Year = {2014}, Month = {July}, ISSN = {0031-9007}, url = {http://dx.doi.org/10.1103/physrevlett.113.020601}, Abstract = {We demonstrate the possibility to systematically steer the most probable escape paths (MPEPs) by adjusting relative noise intensities in dynamical systems that exhibit noise-induced escape from a metastable point via a saddle point. With the use of a geometric minimum action approach, an asymptotic theory is developed that is broadly applicable to fast-slow systems and shows the important role played by the nullcline associated with the fast variable in locating the MPEPs. A two-dimensional quadratic system is presented which permits analytical determination of both the MPEPs and associated action values. Analytical predictions agree with computed MPEPs, and both are numerically confirmed by constructing prehistory distributions directly from the underlying stochastic differential equation.}, Doi = {10.1103/physrevlett.113.020601}, Key = {fds248435} } @article{fds304625, Author = {Bomze, Y and Hey, R and Grahn, HT and Teitsworth, SW}, Title = {Noise-induced current switching in semiconductor superlattices: observation of nonexponential kinetics in a high-dimensional system.}, Journal = {Physical Review Letters}, Volume = {109}, Number = {2}, Pages = {026801}, Year = {2012}, Month = {July}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23030192}, Abstract = {We report on measurements of first-passage-time distributions associated with current switching in weakly coupled GaAs/AlAs superlattices driven by shot noise, a system that is both far from equilibrium and high dimensional. Static current-voltage (I-V) characteristics exhibit multiple current branches and bistability; precision, high-bandwidth current switching data are collected in response to steps in the applied voltage to final voltages V1 near the end of a current branch. For a range of V1 values, the measured switching times vary stochastically. At short times (≲10 μs), the switching time distributions decay exponentially, while at longer times the distributions develop nonexponential tails that follow an approximate power law over several decades. The power law decay behavior is attributed to the presence of multiple switching pathways, which may arise from small spatial variations in the superlattice growth parameters.}, Doi = {10.1103/PhysRevLett.109.026801}, Key = {fds304625} } @article{fds248452, Author = {Bomze, Y and Hey, R and Grahn, HT and Teitsworth, SW}, Title = {Noise-Induced Current Switching in Semiconductor Superlattices: Observation of Nonexponential Kinetics in a High-Dimensional System}, Journal = {Physical Review Letters}, Volume = {109}, Number = {026801}, Pages = {4}, Publisher = {American Physical Society}, Year = {2012}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23030192}, Abstract = {We report on measurements of first-passage-time distributions associated with current switching in weakly coupled GaAs/AlAs superlattices driven by shot noise, a system that is both far from equilibrium and high dimensional. Static current-voltage (I-V) characteristics exhibit multiple current branches and bistability; precision, high-bandwidth current switching data are collected in response to steps in the applied voltage to final voltages near the end of a current branch. For a range of voltage values, the measured switching times vary stochastically. At short times, the switching time distributions decay exponentially, while at longer times the distributions develop nonexponential tails that follow an approximate power law over several decades. The power law decay behavior is attributed to the presence of multiple switching pathways, which may arise from small spatial variations in the superlattice growth parameters.}, Doi = {10.1103/PhysRevLett.109.026801}, Key = {fds248452} } @article{fds248436, Author = {Bonilla, LL and Teitsworth, SW}, Title = {Nonlinear Wave Methods for Charge Transport}, Journal = {Nonlinear Wave Methods for Charge Transport}, Year = {2010}, Month = {September}, url = {http://dx.doi.org/10.1002/9783527628674}, Abstract = {The present book introduces and develops mathematical techniques for the treatment of nonlinear waves and singular perturbation methods at a level that is suitable for graduate students, researchers and faculty throughout the natural sciences and engineering. The practice of implementing these techniques and their value are largely realized by showing their application to problems of nonlinear wave phenomena in electronic transport in solid state materials, especially bulk semiconductors and semiconductor superlattices. The authors are recognized leaders in this field, with more than 30 combined years of contributions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.}, Doi = {10.1002/9783527628674}, Key = {fds248436} } @article{fds248437, Author = {Bonilla, LL and Teitsworth, SW}, Title = {Nonlinear Wave Methods for Charge Transport}, Journal = {Nonlinear Wave Methods for Charge Transport}, Year = {2010}, url = {http://dx.doi.org/10.1002/9783527628674}, Abstract = {The present book introduces and develops mathematical techniques for the treatment of nonlinear waves and singular perturbation methods at a level that is suitable for graduate students, researchers and faculty throughout the natural sciences and engineering. The practice of implementing these techniques and their value are largely realized by showing their application to problems of nonlinear wave phenomena in electronic transport in solid state materials, especially bulk semiconductors and semiconductor superlattices. The authors are recognized leaders in this field, with more than 30 combined years of contributions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.}, Doi = {10.1002/9783527628674}, Key = {fds248437} } @article{fds248449, Author = {Xu, H and Teitsworth, SW}, Title = {Emergence of current branches in a series array of negative differential resistance circuit elements}, Journal = {Journal of Applied Physics}, Volume = {108}, Number = {4}, Pages = {4 pages}, Year = {2010}, ISSN = {0021-8979}, url = {http://arxiv.org/abs/1006.0434v1}, Abstract = {We study a series array of nonlinear electrical circuit elements that possess negative differential resistance and find that heterogeneity in the element properties leads to the presence of multiple branches in current-voltage curves and a nonuniform distribution of voltages across the elements. An inhomogeneity parameter rmax is introduced to characterize the extent to which the individual element voltages deviate from one another, and it is found to be strongly dependent on the rate of change of applied voltage. Analytical expressions are derived for the dependence of rmax on voltage ramping rate in the limit of fast ramping and are confirmed by direct numerical simulation. © 2010 American Institute of Physics.}, Doi = {10.1063/1.3475988}, Key = {fds248449} } @article{fds248450, Author = {Xu, H and Teitsworth, SW}, Title = {On the possibility of a shunt-stabilized superlattice terahertz emitter}, Journal = {Applied Physics Letters}, Volume = {96}, Number = {2}, Year = {2010}, ISSN = {0003-6951}, url = {http://hdl.handle.net/10161/3244 Duke open access}, Abstract = {High field electronic transport through a strongly coupled superlattice (SL) with a shunting side layer is numerically studied using a drift-diffusion model that includes both vertical and lateral dynamics. The bias voltage corresponds to an average electric field in the negative differential conductivity region of the intrinsic current-field curve of the SL, a condition that generally implies space charge instability. Key structural parameters associated with both the shunt layer and SL are identified for which the shunt layer stabilizes a uniform electric field profile. These results support the possibility to realize a SL-based terahertz oscillator with a carefully designed structure. © 2010 American Institute of Physics.}, Doi = {10.1063/1.3291614}, Key = {fds248450} } @article{fds248454, Author = {Xu, H and Teitsworth, SW}, Title = {On the possibility of a shunt-stabilized superlattice THz emitter}, Journal = {Applied Physics Letters}, Volume = {96}, Number = {022101}, Pages = {3 pages}, Year = {2010}, Abstract = {High field electronic transport through a strongly-coupled superlattice (SL) with a shunting side layer is numerically studied using a novel drift-diffusion model. The bias voltage corresponds to an average electric field in the negative differential conductivity (NDC) region of the intrinsic current-field (I ¡ F) curve of the SL, a condition that generally implies space charge instability. Key structural parameters associated with both the shunt layer and SL are identified for which the shunt layer stabilizes a uniform electric field profile. These results support the possibility to realize a SL-based THz oscillator with a carefully designed structure.}, Key = {fds248454} } @article{fds248455, Author = {Heinrich, M and Dahms, T and Flunkert, V and Teitsworth, SW and Schöll, E}, Title = {Symmetry-breaking transitions in networks of nonlinear circuit elements}, Journal = {New Journal of Physics}, Volume = {12}, Number = {113030}, Pages = {32 pages}, Year = {2010}, ISSN = {1367-2630}, url = {http://dx.doi.org/10.1088/1367-2630/12/11/113030}, Abstract = {We investigate a nonlinear circuit consisting of N tunnel diodes in series, which shows close similarities to a semiconductor superlattice or to a neural network. Each tunnel diode is modeled by a three-variable FitzHugh-Nagumo-like system. The tunnel diodes are coupled globally through a load resistor. We find complex bifurcation scenarios with symmetry-breaking transitions that generate multiple fixed points off the synchronization manifold. We show that multiply degenerate zero-eigenvalue bifurcations occur, which lead to multistable current branches, and that these bifurcations are also degenerate with a Hopf bifurcation. These predicted scenarios of multiple branches and degenerate bifurcations are also found experimentally. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.}, Doi = {10.1088/1367-2630/12/11/113030}, Key = {fds248455} } @article{fds248456, Author = {Xu, H and Amann, A and Schoell, E and Teitsworth, SW}, Title = {Dynamics of electronic transport in a semiconductor superlattice with a shunting side layer}, Journal = {Physical Review B}, Volume = {79}, Number = {245318}, Pages = {14}, Year = {2009}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.79.245318}, Abstract = {We study a model describing electronic transport in a weakly coupled semiconductor superlattice with a shunting side layer. Key parameters include the lateral size of the superlattice, the connectivity between the quantum wells of the superlattice and the shunt layer, and the conduction properties of the shunt layer. For a superlattice with small lateral extent and high quality shunt, static electric field domains are suppressed and a spatially uniform field configuration is predicted to be stable, results that may be useful for proposed devices such as a superlattice-based terahertz oscillators. As the lateral size of the superlattice increases, the uniform field configuration loses its stability to either static or dynamic field domains regardless of shunt properties. A lower quality shunt generally leads to regular and chaotic current oscillations and complex spatiotemporal dynamics in the field profile. Bifurcations separating static and dynamic behaviors are characterized and found to be dependent on the shunt properties.}, Doi = {10.1103/PhysRevB.79.245318}, Key = {fds248456} } @article{fds304624, Author = {Xu, H and Amann, A and Schöll, E and Teitsworth, SW}, Title = {Dynamics of electronic transport in a semiconductor superlattice with a shunting side layer}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {79}, Number = {24}, Year = {2009}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.79.245318}, Abstract = {We study a model describing electronic transport in a weakly coupled semiconductor superlattice with a shunting side layer. Key parameters include the lateral size of the superlattice, the connectivity between the quantum wells of the superlattice and the shunt layer, and the conduction properties of the shunt layer. For a superlattice with small lateral extent and high quality shunt, static electric field domains are suppressed and a spatially uniform field configuration is predicted to be stable, results that may be useful for proposed devices such as a superlattice-based terahertz oscillators. As the lateral size of the superlattice increases, the uniform field configuration loses its stability to either static or dynamic field domains regardless of shunt properties. A lower quality shunt generally leads to regular and chaotic current oscillations and complex spatiotemporal dynamics in the field profile. Bifurcations separating static and dynamic behaviors are characterized and found to be dependent on the shunt properties. © 2009 The American Physical Society.}, Doi = {10.1103/PhysRevB.79.245318}, Key = {fds304624} } @article{fds248453, Author = {Xu, H and Teitsworth, SW}, Title = {Dependence of electric field domain relocation dynamics on contact conductivity in semiconductor superlattices}, Journal = {Physical Review B}, Volume = {76}, Number = {235302}, Pages = {11 pages}, Year = {2007}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.76.235302}, Abstract = {Numerical simulation results are presented for a discrete drift-diffusion rate equation model that describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor superlattices. We study the dependence on contact conductivity σ of current-voltage characteristics and transient current response to abrupt steps in applied voltage. For intermediate values of σ, three qualitatively distinct transient responses—each associated with a different mechanism for the relocation of a static charge accumulation layer—are observed for different values of voltage step Vstep; these involve, respectively, (1) the motion of a single charge accumulation layer, (2) the motion of an injected charge dipole, and (3) the motion of an injected monopole. A critical value of σ is identified above which the injected dipole mechanism is not observed for any value of Vstep. Furthermore, at very low σ, we find a reversed static field configuration, i.e., with the high-field domain adjacent to the emitter contact.}, Doi = {10.1103/PhysRevB.76.235302}, Key = {fds248453} } @article{fds304623, Author = {Xu, H and Teitsworth, SW}, Title = {Dependence of electric field domain relocation dynamics on contact conductivity in semiconductor superlattices}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {76}, Number = {23}, Year = {2007}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.76.235302}, Abstract = {Numerical simulation results are presented for a discrete drift-diffusion rate equation model that describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor superlattices. We study the dependence on contact conductivity σ of current-voltage characteristics and transient current response to abrupt steps in applied voltage. For intermediate values of σ, three qualitatively distinct transient responses-each associated with a different mechanism for the relocation of a static charge accumulation layer-are observed for different values of voltage step Vstep; these involve, respectively, (1) the motion of a single charge accumulation layer, (2) the motion of an injected charge dipole, and (3) the motion of an injected monopole. A critical value of σ is identified above which the injected dipole mechanism is not observed for any value of Vstep. Furthermore, at very low σ, we find a reversed static field configuration, i.e., with the high-field domain adjacent to the emitter contact. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevB.76.235302}, Key = {fds304623} } @article{fds248458, Author = {Lu, SL and Schrottke, L and Teitsworth, SW and Hey, R and Grahn, HT}, Title = {Negative differential conductance and bistability in undoped GaAs/AlGaAs quantum-cascade structures}, Journal = {Journal of Applied Physics}, Volume = {100}, Number = {023701}, Pages = {6 pages}, Year = {2006}, Month = {July}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.2214362}, Abstract = {We discuss the mechanisms for negative differential conductance NDC and bistable behavior observed in the current-density–electric-field j-F characteristics of undoped GaAs/Al0.45Ga0.55As quantum-cascade structures QCSs . While the j-F characteristic of a QCS with a single period exhibits NDC without bistability, NDC and a bistable behavior are observed for a QCS with 20 periods of the same design. Calculations using a scattering-rate model neglecting any field inhomogeneities show that the interplay of resonant tunneling between the states in the QCS with resonant scattering of longitudinal optical phonons can lead to NDC in both structures. However, the bistable behavior in the QCS with 20 periods can only be explained if an inhomogeneous field distribution due to charge accumulation is taken into account in addition to the NDC. The abrupt decrease of the current density at the field strength of the bistability is attributed to a rapid decrease of the accumulated charge, which is confirmed by electric-field-dependent photoluminescence spectroscopy.}, Doi = {10.1063/1.2214362}, Key = {fds248458} } @article{fds248457, Author = {Lu, SL and Schrottke, L and Teitsworth, SW and Hey, R and Grahn, HT}, Title = {Formation of electric-field domains in GaAs/AlGaAs quantum cascade laser structures}, Journal = {Physical Review B}, Volume = {73}, Number = {033311}, Pages = {4 pages}, Year = {2006}, Month = {January}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.73.033311}, Abstract = {The current-voltage (I-V ) characteristics of GaAs/AlGaAs quantum-cascade laser structures (QCLSs) are found to exhibit current plateaus with discontinuities for voltages below threshold. The number of current discontinuities is correlated with the number of periods of the QCLS, suggesting the formation of electric-field domains that span the entire structure. A self-consistent calculation of the conduction band profile and corresponding electronic wave functions shows that the low-field domain is related to resonant tunneling between the ground state g in the active region and the lowest energy state in the adjacent, downstream injector i1. For x = 0.33 (x = 0.45), the high-field domain is formed for resonant tunneling between g and the first (second) excited state i2 (i3) in the injector region. A comparison of the experimental data with the calculated conduction band profile shows that a significant field inhomogeneity within each period shifts the voltage range, for which the resonance condition is fulfilled, to much lower voltages than expected for a homogeneous field distribution.}, Doi = {10.1103/PhysRevB.73.033311}, Key = {fds248457} } @article{fds304621, Author = {Lu, SL and Schrottke, L and Teitsworth, SW and Hey, R and Grahn, HT}, Title = {Formation of electric-field domains in GaAs Alx Ga1-x As quantum cascade laser structures}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {73}, Number = {3}, Year = {2006}, ISSN = {1098-0121}, url = {http://dx.doi.org/10.1103/PhysRevB.73.033311}, Abstract = {The current-voltage (I-V) characteristics of GaAs Alx Ga1-x As quantum cascade laser structures (QCLSs) are found to exhibit current plateaus with discontinuities for voltages below threshold. The number of current discontinuities is correlated with the number of periods of the QCLS, suggesting the formation of electric-field domains that span the entire structure. A self-consistent calculation of the conduction band profile and corresponding electronic wave functions shows that the low-field domain is related to resonant tunneling between the ground state g in the active region and the lowest energy state in the adjacent, downstream injector i1. For x=0.33 (x=0.45), the high-field domain is formed for resonant tunneling between g and the first (second) excited state i2 (i3) in the injector region. A comparison of the experimental data with the calculated conduction band profile shows that a significant field inhomogeneity within each period shifts the voltage range, for which the resonance condition is fulfilled, to much lower voltages than expected for a homogeneous field distribution. © 2006 The American Physical Society.}, Doi = {10.1103/PhysRevB.73.033311}, Key = {fds304621} } @article{fds304622, Author = {Lu, SL and Schrottke, L and Teitsworth, SW and Hey, R and Grahn, HT}, Title = {Negative differential conductance and bistability in undoped GaAs/(Al,Ga)As quantum-cascade structures}, Journal = {Journal of Applied Physics}, Volume = {100}, Number = {2}, Year = {2006}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.2214362}, Abstract = {We discuss the mechanisms for negative differential conductance (NDC) and bistable behavior observed in the current-density-electric-field (j-F) characteristics of undoped GaAs/Al 0.45Ga 0.55As quantum-cascade structures (QCSs). While the j-F characteristic of a QCS with a single period exhibits NDC without bistability, NDC and a bistable behavior are observed for a QCS with 20 periods of the same design. Calculations using a scattering-rate model neglecting any field inhomogeneities show that the interplay of resonant tunneling between the states in the QCS with resonant scattering of longitudinal optical phonons can lead to NDC in both structures. However, the bistable behavior in the QCS with 20 periods can only be explained if an inhomogeneous field distribution due to charge accumulation is taken into account in addition to the NDC. The abrupt decrease of the current density at the field strength of the bistability is attributed to a rapid decrease of the accumulated charge, which is confirmed by electric-field-dependent photoluminescence spectroscopy. © 2006 American Institute of Physics.}, Doi = {10.1063/1.2214362}, Key = {fds304622} } @article{fds248490, Author = {Rogozia, M and Teitsworth, SW and Grahn, HT and Ploog, KH}, Title = {Relocation dynamics of domain boundaries in semiconductor superlattices}, Journal = {Physical Review B}, Volume = {65}, Number = {205303}, Pages = {1-7}, Year = {2002}, ISSN = {0163-1829}, Abstract = {The formation of static electric-field domains in doped semiconductor superlattices appears in the current-voltage (I-V) characteristics as multiple current branches separated by abrupt discontinuities. The switching dynamics of the charge-accumulation layer forming the domain boundary is experimentally investigated at dc voltages in the first plateau of the I-V characteristic for different polarities and amplitudes of the applied voltage steps. When the voltage is decreased (down jumps) from its initial dc value, the accumulation layer can directly move from its initial position to its final position, in accordance with the direction of the applied voltage step. However, when the voltage is increased (up jumps), there are two different modes of the relocation motion of the accumulation layer. For small up jumps, the accumulation layer can still move directly from its initial to its final position. When the amplitude of the transient current peak is above a critical value, a charge dipole is injected at the emitter contact, in addition to the existing monopole formed by the domain boundary. The experimentally observed switching behavior is in excellent qualitative agreement with recent theoretical work [A. Amann et al., Phys. Rev. E 63, 066207 (2001)].}, Key = {fds248490} } @article{fds248491, Author = {Rogozia, M and Grahn, HT and Teitsworth, SW and Ploog, KH}, Title = {Time distribution of the domain-boundary relocation in superlattices}, Journal = {Physica B: Condensed Matter}, Volume = {314}, Number = {1-4}, Pages = {427-430}, Year = {2002}, ISSN = {0921-4526}, url = {http://dx.doi.org/10.1016/S0921-4526(01)01387-4}, Abstract = {Static domain formation in doped, weakly coupled semiconductor superlattices results in several current branches separated by discontinuities that exhibit hysteresis. The transition from one branch to its adjacent higher and lower one is studied by time-resolved switching experiments. The distribution function of the relocation time for up and down jumps changes from a simple Gaussian to a first-passage time (FPT) form, when the final voltage on the adjacent branch approaches a discontinuity in the current-voltage characteristic. This observation indicates that for a smaller voltage distance from the discontinuity (FPT distribution) the system reaches the final state via an unstable intermediate state. In contrast, for a larger voltage distance from the discontinuity (Gaussian distribution), the system arrives directly at the final state, because the intermediate state does not exist. © 2002 Elsevier Science B.V. All rights reserved.}, Doi = {10.1016/S0921-4526(01)01387-4}, Key = {fds248491} } @article{fds304620, Author = {Rogozia, M and Teitsworth, SW and Grahn, HT and Ploog, KH}, Title = {Relocation dynamics of domain boundaries in semiconductor superlattices}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {65}, Number = {20}, Pages = {2053031-2053037}, Year = {2002}, ISSN = {0163-1829}, Abstract = {The formation of static electric-field domains in doped semiconductor superlattices appears in the current-voltage (I-V) characteristics as multiple current branches separated by abrupt discontinuities. The switching dynamics of the charge-accumulation layer forming the domain boundary is experimentally investigated at dc voltages in the first plateau of the I-V characteristic for different polarities and amplitudes of the applied voltage steps. When the voltage is decreased (down jumps) from its initial dc value, the accumulation layer can directly move from its initial position to its final position, in accordance with the direction of the applied voltage step. However, when the voltage is increased (up jumps), there are two different modes of the relocation motion of the accumulation layer. For small up jumps, the accumulation layer can still move directly from its initial to its final position. When the amplitude of the transient current peak is above a critical value, a charge dipole is injected at the emitter contact, in addition to the existing monopole formed by the domain boundary. The experimentally observed switching behavior is in excellent qualitative agreement with recent theoretical work [A. Amann et al., Phys. Rev. E 63, 066207 (2001)].}, Key = {fds304620} } @article{fds4222, Author = {K. J. Luo and S.W. Teitsworth and M. Rogozia and H. T. Grahn and L. Bonilla, J. Galan and N. Ohtani}, Title = {Controllable bifurcation processes in undoped, photoexcited GaAs/AlAs superlattices}, Series = {World Scientific}, Booktitle = {Proceedings of the 5th experimental chaos conference}, Editor = {M. Ding et al.}, Year = {2001}, Key = {fds4222} } @article{fds248441, Author = {Cantalapiedra, IR and Bergmann, MJ and Bonilla, LL and Teitsworth, SW}, Title = {Chaotic motion of space charge wave fronts in semiconductors under time-independent voltage bias}, Journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, Volume = {63}, Number = {5 II}, Pages = {562161-562167}, Year = {2001}, url = {http://arxiv.org/abs/cond-mat/0011162v1}, Abstract = {The chaos under dc voltage bias linked with multiple shedding of wave fronts were numerically simulated. Space charge wave dynamics was analyzed with a finite-dimensional model. Drift diffusion model of space charge wave propagation in semiconductors was studied. The dynamics of space charge waves and current vs time were explained by asymptotic analysis of a partial differential equation model. It was found that single or multiple wave shedding during each oscillation depend on resistivity of the injecting contacts.}, Doi = {10.1103/PhysRevE.63.056216}, Key = {fds248441} } @article{fds248487, Author = {Rogozia, M and Teitsworth, SW and Grahn, HT and Ploog, K}, Title = {Statistics of the domain boundary relocation time in semiconductor superlattices}, Journal = {Physical Review B - Rapid Communications}, Volume = {64}, Number = {041308}, Pages = {1-4}, Year = {2001}, ISSN = {0163-1829}, Abstract = {Static domain formation in doped semiconductor superlattices results in several current branches separated by abrupt discontinuities that exhibit hysteresis. The transition from one branch to its adjacent one is studied by time-resolved switching experiments. The mean value of the relocation time increases by more than one order of magnitude, when the final voltage on the adjacent branch is reduced to a value approaching the discontinuity. At the same time, the distribution function of the relocation time changes from a simple Gaussian to a first-passage time form.}, Key = {fds248487} } @article{fds304619, Author = {Rogozia, M and Teitsworth, SW and Grahn, HT and Ploog, KH}, Title = {Statistics of the domain-boundary relocation time in semiconductor superlattices}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {64}, Number = {4}, Pages = {413081-413084}, Year = {2001}, ISSN = {0163-1829}, Abstract = {Static domain formation in doped semiconductor superlattices results in several current branches separated by abrupt discontinuities that exhibit hysteresis. The transition from one branch to its adjacent one is studied by time-resolved switching experiments. The mean value of the relocation time increases by more than one order of magnitude, when the final voltage on the adjacent branch is reduced to a value approaching the discontinuity. At the same time, the distribution function of the relocation time changes from a simple Gaussian to a first-passage time form.}, Key = {fds304619} } @article{fds4224, Author = {S.W. Teitsworth}, Title = {Quantum chaos effects in mechanical wave systems}, Series = {Springer-Verlag}, Booktitle = {Proceedings of the 16th Sitges conference}, Editor = {D. Reguera et al.}, Year = {2000}, Key = {fds4224} } @article{fds248488, Author = {Olafsen, LJ and Daniels-Race, T and Kendall, RE and Teitsworth, SW}, Title = {Photoluminescence of n-i-n GaAs/AlAs single quantum well structures under electric field bias}, Journal = {Superlattices and Microstructures}, Volume = {27}, Number = {1}, Pages = {7-14}, Year = {2000}, ISSN = {0749-6036}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000085519800006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {GaAs/AlAs single quantum well structures designed with well thickness near the type-I/type-II crossover show distinctive photoluminescence peaks corresponding to both type-I and type-II recombinations. Photoluminescence measurements as a function of applied electric field and temperature ranging from 23 to 180 K and current-voltage measurements are presented for two MBE-grown structures clad with Si-doped Al0.45Ga0.55As layers on n+-GaAs [100] substrates. The large and field-dependent energy separation between type-I and type-II luminescence peaks is understood to arise from the build-up of electrons at the X point in the AlAs barrier.}, Doi = {10.1006/spmi.1999.0811}, Key = {fds248488} } @article{fds248489, Author = {Luo, KJ and Teitsworth, SW and Kostial, H and Grahn, HT and Ohtani, N}, Title = {Controllable bistabilities and bifurcations in a photoexcited GaAs/AlAs superlattice}, Journal = {Applied Physics Letters}, Volume = {74}, Number = {25}, Pages = {3845-3847}, Year = {1999}, Abstract = {Self-sustained photocurrent oscillations and bifurcation process have been demonstrated on an undoped photoexcited GaAs/AlAs superlattice. The effects of carrier density, varied by changing the laser intensity, on the transition between static and oscillating domains are investigated. Within a certain range of intermediate intensities, the time-average photocurrent vs voltage plot exhibits a controllable bistability region near the edge of the first photocurrent plateau and the oscillations disappear via a subcritical Hopf bifurcation (HB) with increasing DC bias. Below this range, the oscillations disappear via a supercritical HB, while above it, a homoclinic connection is observed.}, Key = {fds248489} } @booklet{Luo98, Author = {Luo, KJ and Grahn, HT and Teitsworth, SW and Ploog, KH}, Title = {Influence of higher harmonics on Poincaré maps derived from current self-oscillations in a semiconductor superlattice}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {58}, Number = {19}, Pages = {12613-12616}, Year = {1998}, Abstract = {The effect of higher harmonics on the shape of Poincaré maps (first return maps) derived from current self-oscillations has been investigated in a semiconductor superlattice system driven by a dc + ac voltage bias. In addition to the intrinsic fundamental frequency, a number of higher harmonics with comparable amplitude are observed. The current oscillation traces are simulated according to the power spectra in order to determine, the effect of the higher harmonics on the Poincaré maps. The calculated Poincaré maps for quasiperiodic oscillations as well as frequency locking are clearly distorted by the presence of the higher harmonics. The shape of the distorted Poincaré maps agrees with the experimentally observed ones. The calculation also reveals that the phase shift between the different frequency components of the current has an important effect on the shape of the Poincaré maps. © 1998 The American Physical Society.}, Key = {Luo98} } @booklet{Blue97, Author = {Blue, LJ and Daniels-Race, T and Kendall, RE and Schmid, CR and Teitsworth, SW}, Title = {Dependence of current-voltage characteristics on Al mole fraction in GaAs/Al_{x}Ga_{1-x}As asymmetric double barrier structures}, Journal = {Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures}, Volume = {15}, Number = {3}, Pages = {696-701}, Year = {1997}, Abstract = {The effect of barrier Al mole fraction, 0.2≤x≤0.8. on tunneling currents has been studied for a set of asymmetric GaAs/AlxGa1-xAs double barrier structures. The barrier widths of each sample were scaled so that barrier transmission coefficients for different samples should be approximately equivalent at the first resonant tunneling peak. Structures were grown by molecular beam epitaxy; by adjusting Ga and Al cell temperatures, the full range of Al mole fractions could be achieved in AlxGa1-xAs barrier layers while maintaining a nearly constant growth rate of about 1 μm/h. Current-voltage measurements are in agreement with theoretical estimates and indicate good sample quality. © 1997 American Vacuum Society.}, Key = {Blue97} } @booklet{Bergmann96, Author = {Bergmann, MJ and Teitsworth, SW and Bonilla, LL and Cantalapiedra, IR}, Title = {Solitary-wave conduction in p-type Ge under time-dependent voltage bias.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {53}, Number = {3}, Pages = {1327-1335}, Year = {1996}, Month = {January}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9983592}, Key = {Bergmann96} } @booklet{Banoo96, Author = {Banoo, K}, Title = {Phonon scattering in novel superlattice-asymmetric double barrier resonant tunneling structure}, Journal = {Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures}, Volume = {14}, Number = {4}, Pages = {2725-2730}, Year = {1996}, Abstract = {The scattering effects (specifically LO-phonon scattering) in a 45 Å AlAs/80 Å GaAs/33 A AlAs asymmetric double barrier resonant tunneling (ADBRT) structure with a short period GaAS/Al0.3Ga0.7As superlattice incorporated on one side of the double barrier have been studied and characterized. Enhanced levels of current conduction were produced in the ADBRT due to the superlattice miniband electron transport under forward bias. And the effect of the said superlattice on the phonon scattering phenomena exhibited by the entire device was subsequently examined. Magnetic field fan diagrams at 4.2 K under reverse bias showed a new feature at an energy of 22 meV that could be explained on the basis of previously unreported GaAs LO-phonon scattering processes from the first excited emitter level. Finally, quenching of phonon-assisted tunneling in reverse bias on decreasing the period of the superlattice was also observed. © 1996 American Vacuum Society.}, Key = {Banoo96} } @booklet{Delacruz95, Author = {de la Cruz RM, and Teitsworth, SW and Stroscio, MA}, Title = {Interface phonons in spherical GaAs/AlxGa1-xAs quantum dots.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {52}, Number = {3}, Pages = {1489-1492}, Year = {1995}, Month = {July}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9981202}, Key = {Delacruz95} } @booklet{Turley95, Author = {Turley, PJ and Wallis, CR and Teitsworth, SW}, Title = {Selection rule for localized phonon emission in GaAs/AlAs double-barrier structures}, Journal = {Journal of Applied Physics}, Volume = {78}, Number = {10}, Pages = {6104-6107}, Year = {1995}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.360551}, Abstract = {Phonon-assisted tunneling (PAT) has been studied in detail for two similar GaAs/AlAs double-barrier structures. Calculations of the PAT current - including effects of optical-phonon localization - are in good agreement with experimental data, and the emission rate for certain phonon types is found to depend sensitively on GaAs well width. We find that GaAs-like modes clearly dominate in structures with wider wells, while GaAs and AlAs-like modes contribute equivalently in narrower well structures. A simple overlap integral - involving the phonon potential and electronic wave functions - provides an effective selection rule for determining which types of phonons are preferentially emitted. © 1995 American Institute of Physics.}, Doi = {10.1063/1.360551}, Key = {Turley95} } @booklet{Turley94, Author = {Turley, PJ and Teitsworth, SW}, Title = {Phonon-assisted tunneling from a two-dimensional emitter state.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {50}, Number = {12}, Pages = {8423-8432}, Year = {1994}, Month = {September}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9974860}, Key = {Turley94} } @booklet{Wallis94, Author = {Wallis, CR and Teitsworth, SW}, Title = {Hopf bifurcations and hysteresis in resonant tunneling diode circuits}, Journal = {Journal of Applied Physics}, Volume = {76}, Number = {7}, Pages = {4443-4445}, Year = {1994}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.357343}, Abstract = {Conditions for Hopf bifurcations and associated current oscillations are presented for a standard model of a resonant tunneling diode circuit. We derive a simple analytic formula for the Hopf bifurcation type (subcritical or supercritical) and discuss how this affects circuit operation, e.g., whether or not hysteresis and bistability are observed in current-voltage curves.}, Doi = {10.1063/1.357343}, Key = {Wallis94} } @booklet{Bonilla94, Author = {Bonilla, LL and Bergmann, MJ and Cantalapiedra, IR and Teitsworth, SW}, Title = {Onset of current oscillations in extrinsic semiconductors under DC voltage bias}, Journal = {Semiconductor Science and Technology}, Volume = {9}, Number = {5 SUPPL}, Pages = {599-602}, Year = {1994}, ISSN = {0268-1242}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:A1994NM75300054&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We present a model which describes the onset of current instabilities and space-charge domains in extrinsic semiconductors (especially p-Ge) under DC voltage bias. Just above the onset voltage for current instability we have found numerically small-amplitude fast oscillations due to the periodic motion of solitary waves which decay before reaching the receiving contact. For slightly larger applied voltages there is an abrupt and slightly hysteretic transition to slower large-amplitude solitary waves similar to those in the Gunn effect. An amplitude oscillatory modes that become linearly unstable at onset.}, Doi = {10.1088/0268-1242/9/5S/054}, Key = {Bonilla94} } @booklet{Teitsworth94, Author = {Bhattacharya, PK and Li, W and Wallis, CR and Turley, PJ and Teitsworth, SW}, Title = {Magnetotunnelling measurements of localized optical phonons in GaAs/AlAs double-barrier structures}, Journal = {Semiconductor Science and Technology}, Volume = {9}, Number = {5 SUPPL}, Pages = {508-511}, Year = {1994}, ISSN = {0268-1242}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:A1994NM75300029&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We have measured current-voltage characteristics at liquid-helium temperature and for magnetic fields up to 7 T (parallel to the current flow) for three similar asymmetric GaAs/AlAs double-barrier structures, all of which possess large phonon-assisted tunnelling currents. Confined longitudinal optical (LO) phonons on the GaAs well layer and LO-like symmetric interface phonons treated within a dielectric continuum picture suffice to account for the measured currents. Phonon-assisted tunnelling current levels as well as magnetotunnelling data are found depend sensitively on well and barrier widths.}, Doi = {10.1088/0268-1242/9/5S/029}, Key = {Teitsworth94} } @booklet{Cantalapiedra93, Author = {Cantalapiedra, IR and Bonilla, LL and Bergmann, MJ and Teitsworth, SW}, Title = {Solitary-wave dynamics in extrinsic semiconductors under dc voltage bias.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {48}, Number = {16}, Pages = {12278-12281}, Year = {1993}, Month = {October}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10007580}, Key = {Cantalapiedra93} } @booklet{Turley93, Author = {Turley, PJ and Wallis, CR and Teitsworth, SW and Li, W and Bhattacharya, PK}, Title = {Tunneling measurements of symmetric-interface phonons in GaAs/AlAs double-barrier structures.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {47}, Number = {19}, Pages = {12640-12648}, Year = {1993}, Month = {May}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10005459}, Key = {Turley93} } @booklet{Delacruz93, Author = {Cruz, RMD and Teitsworth, SW and Stroscio, MA}, Title = {Bottleneck effects due to confined phonons in quantum dots}, Journal = {Superlattices and Microstructures}, Volume = {13}, Number = {4}, Pages = {481-}, Year = {1993}, ISSN = {0749-6036}, url = {http://dx.doi.org/10.1006/spmi.1993.1090}, Abstract = {A generalization of the three-dimensional Fröhlich hamiltonian for a polar semiconductor is presented which describes the interaction between charge carriers of a zero-dimensional electron gas and longitudinal optical (LO) phonon modes confined in three spatial dimensions. This hamiltonian is used to calculate the scattering rate of electrons by LO phonons in a GaAs quantum box which is free-standing in vacuum. The suppression of scattering through a phonon bottleneck effect is discussed in terms of the selection rules. © 1993 Academic Press. All rights reserved.}, Doi = {10.1006/spmi.1993.1090}, Key = {Delacruz93} } @booklet{Turley92, Author = {Turley, PJ and Teitsworth, SW}, Title = {Theory of localized phonon modes and their effects on electron tunneling in double-barrier structures}, Journal = {Journal of Applied Physics}, Volume = {72}, Number = {6}, Pages = {2356-2366}, Year = {1992}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.351577}, Abstract = {The role of localized phonon modes in phonon-assisted tunneling in GaAs/AlAs double-barrier resonant tunneling structures is considered for a range of temperatures and magnetic fields. Phonon modes are calculated using a dielectric continuum model and electron-phonon Hamiltonians are presented for the most important modes. Formulas for phonon-assisted tunneling currents are derived that express the inherently three-dimensional process in a simple one-dimensional form. It is found that the excess current due to phonon-assisted tunneling in typical structures is caused primarily by two types of localized modes: confined modes in the well and symmetric interface modes, with interface modes dominating in structures with narrow wells. Current peaks broaden with increasing temperature, and for temperatures ≳20 K the resolution of features due to distinct phonon types is very difficult. The application of a magnetic field parallel to the current flow leads to a complex spectrum of sharp current peaks corresponding to various inter-Landau-level transitions which occur during phonon-assisted tunneling.}, Doi = {10.1063/1.351577}, Key = {Turley92} } @booklet{Kim92, Author = {Kim, KW and Bhatt, AR and Stroscio, MA and Turley, PJ and Teitsworth, SW}, Title = {Effects of interface phonon scattering in multiheterointerface structures}, Journal = {Journal of Applied Physics}, Volume = {72}, Number = {6}, Pages = {2282-2287}, Year = {1992}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.351569}, Abstract = {In this paper, the commonly used but idealistic formulation of quantized optical-phonon modes for a heterostructure system with only two heterojunctions (i.e., single quantum-well structures) is extended to the more realistic case of multiheterointerface structures. By applying the macroscopic dielectric continuum approach, dispersion relations and interaction Hamiltonians for interface-phonon modes are derived for a double-barrier structure and scattering rates based on these results are used to determine the range of practical validity of the idealistic model using interaction Hamiltonians appropriate for single quantum wells with infinite barrier widths. It is found that when the dimensions of the structures are larger than approximately 30 Å, this simplified description can be applied to multiheterointerface structures in general with reasonable accuracy.}, Doi = {10.1063/1.351569}, Key = {Kim92} } @booklet{Turley91, Author = {Turley, PJ and Teitsworth, SW}, Title = {Effects of localized phonon modes on magnetotunneling spectra in double-barrier structures.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {44}, Number = {23}, Pages = {12959-12963}, Year = {1991}, Month = {December}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9999478}, Key = {Turley91} } @booklet{Turley91a, Author = {Turley, PJ and Teitsworth, SW}, Title = {Phonon-assisted tunneling due to localized modes in double-barrier structures.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {44}, Number = {15}, Pages = {8181-8184}, Year = {1991}, Month = {October}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9998750}, Key = {Turley91a} } @booklet{Turley91b, Author = {Turley, PJ and Teitsworth, SW}, Title = {Electronic wave functions and electron-confined-phonon matrix elements in GaAs/AlxGa1-xAs double-barrier resonant-tunneling structures.}, Journal = {Physical Review B - Condensed Matter and Materials Physics}, Volume = {44}, Number = {7}, Pages = {3199-3210}, Year = {1991}, Month = {August}, ISSN = {0163-1829}, url = {http://www.ncbi.nlm.nih.gov/pubmed/9999916}, Key = {Turley91b} } @booklet{Bonilla91, Author = {Bonilla, LL and Teitsworth, SW}, Title = {Theory of periodic and solitary space charge waves in extrinsic semiconductors}, Journal = {Physica D: Nonlinear Phenomena}, Volume = {50}, Number = {3}, Pages = {545-559}, Year = {1991}, ISSN = {0167-2789}, Abstract = {We present a theory of the existence and stability of traveling periodic and solitary space charge wave solutions to a standard rate equation model of electrical conduction in extrinsic semiconductors which includes effects of field-dependent impurity impact ionization. A nondimensional set of equations is presented in which the small parameter β = (dielectric relaxation time) / (characteristic impurity time) ≫ 1 plays a crucial role for our singular perturbation analysis. For a narrow range of wave velocities a phase plane analysis gives a set of limit cycle orbits corresponding to periodic traveling waves. while for a unique value of wave velocity we find a homoclinic orbit corresponding to a moving solitary space charge wave of the type experimentally observed in p-type germanium. A linear stability analysis reveals all waves to be unstable under current bias on the infinite one-dimensional line. Finally, we conjecture that solitary waves may be stable in samples of finite length under voltage bias. © 1991.}, Key = {Bonilla91} } @booklet{Teitsworth89, Author = {Teitsworth, SW}, Title = {Physics of space charge instabilities and temporal chaos in extrinsic photoconductors}, Journal = {Applied Physics A: Solids and Surfaces}, Volume = {48}, Number = {2}, Pages = {127-136}, Year = {1989}, Abstract = {This paper reviews experimental and theoretical work carried out on space charge instabilities and temporal chaotic behavior in cooled extrinsic p-type Germanium photoconductors. Measured dc current-voltage (I-V) characteristics of these devices are strongly nonlinear for moderate electric field ≥0.1 V/cm due to field dependence of the rates of free hole capture and impurity impact ionization. Below the threshold field for impurity breakdown, Ge samples behave like damped nonlinear oscillators, exhibiting characteristic chaotic response when driven by a time-periodic voltage. Above impurity breakdown, we observe voltage-controlled negative differential resistance (NDR) in the I-V curves accompanied by spontaneous current oscillations due to moving space charge domains with velocities 103 to 104 cm/s. Measurements are well explained by a simple rate equation model in which negative differential behavior in the impact ionization rate plays a crucial role. Related work on semiconductor chaos and possible future directions for research are also mentioned.}, Key = {Teitsworth89} } @booklet{Teitsworth86b, Author = {Teitsworth, SW and Westervelt, RM}, Title = {Subharmonic and chaotic response of periodically driven extrinsic Ge photoconductors.}, Journal = {Physical Review Letters}, Volume = {56}, Number = {5}, Pages = {516-519}, Year = {1986}, Month = {February}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10033212}, Doi = {10.1103/PhysRevLett.56.516}, Key = {Teitsworth86b} } @booklet{Teitsworth86, Author = {TEITSWORTH, SW and LYNN, BA and WESTERVELT, RM}, Title = {CHAOTIC DYNAMICS IN A SIMPLE-MODEL OF EXTRINSIC PHOTOCONDUCTORS}, Journal = {Physica Scripta T}, Volume = {T14}, Pages = {71-75}, Year = {1986}, ISSN = {0281-1847}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:A1986H841100014&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Doi = {10.1088/0031-8949/1986/T14/012}, Key = {Teitsworth86} } @booklet{Teitsworth86a, Author = {Teitsworth, SW and Westervelt, RM}, Title = {Nonlinear current-voltage characteristics and spontaneous current oscillations in p-Ge}, Journal = {Physica D: Nonlinear Phenomena}, Volume = {23}, Number = {1-3}, Pages = {181-186}, Year = {1986}, ISSN = {0167-2789}, Abstract = {We report an experimental measurement of nonlinear dc current-voltage (I-V) characteristics in p-type Ge extrinsic photoconductors at liquid He temperatures which exhibit a region of voltage-controlled negative differential resistance (NDR) above the threshold for impurity breakdown, accompanied by a spontaneous current oscillation of frequency fs ∼ 5 to 10 kHz. The dc I-V characteristics are well explained in terms of a simple rate equation model and, it is argued, the spontaneous current oscillations are due to moving space charge waves which arise from a negative differential rate of impurity impact ionization. © 1986.}, Key = {Teitsworth86a} } @booklet{Westervelt86, Author = {WESTERVELT, RM and TEITSWORTH, SW and GWINN, EG}, Title = {CHAOTIC DYNAMICS IN GE PHOTOCONDUCTORS}, Journal = {Physica Scripta T}, Volume = {T14}, Number = {C}, Pages = {65-70}, Year = {1986}, ISSN = {0281-1847}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:A1986H841100013&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {Experimental tests are presented of universal predictions of the circle map for the response of driven nonlinear oscillators, using a spatio-temporal instability associated with impurity impact ionization in liquid He cooled p-type Ge. Both the measured power spectrum and the spectrum of dimensions f (α) for drive at the critical amplitude for winding number equal to the golden mean are found to be in quantitative agreement with theory. © 1987.}, Doi = {10.1088/0031-8949/1986/T14/011}, Key = {Westervelt86} } @booklet{Westervelt86a, Author = {Westervelt, RM and Teitsworth, SW}, Title = {Nonlinear dynamics and chaos in extrinsic photoconductors}, Journal = {Physica D: Nonlinear Phenomena}, Volume = {23}, Number = {1-3}, Pages = {187-194}, Year = {1986}, ISSN = {0167-2789}, Abstract = {We present an experimental and theoretical analysis of the nonlinear response of cooled extrinsic Ge photoconductors of the type used to detect far-infrared radiation. State of the art p-type Ge devices with nearly ideal noise performance in the absence of drive show characteristic subharmonic and chaotic nonlinear phenomena when periodically driven, with a corresponding degredation in noise performance by a factor ≈ 104. A systematic series of experiments and corresponding simulations of a standard model of extrinsic photoconductors, including measurings and simulations of the I-V curves, transient and small signal response, as well as the response to periodic drive, identify the physical transport processes responsible: the nonlinear electric field dependence of the rates of free hole capture and impact ionization due to carrier heating at relatively modest applied electric fields E > 0.1 V/cm. © 1986.}, Key = {Westervelt86a} } @booklet{Westervelt85, Author = {Westervelt, RM and Teitsworth, SW}, Title = {Nonlinear transient response of extrinsic Ge far-infrared photoconductors}, Journal = {Journal of Applied Physics}, Volume = {57}, Number = {12}, Pages = {5457-5469}, Year = {1985}, ISSN = {0021-8979}, url = {http://dx.doi.org/10.1063/1.334822}, Abstract = {Physical mechanisms responsible for nonlinear phenomena and anomalous transient response of cooled extrinsic far-infrared photoconductors are discussed. A simple model describing carrier generation, trapping, and impact ionization is presented, which describes the transient response on fast time scales 10-3 to 10-4 sec, neglecting changes in space charge. Carrier heating by a dc electric field produces relatively fast, damped oscillatory response to external excitation. A small-signal analysis of these equations is a test of stability. An analysis of the role of ideal electrical contacts and space charge is also presented. The very slow (∼1 sec) overshoot and transient response commonly observed in cooled extrinsic photoconductors is explained by the dynamics of trapped space charge near the injecting electrical contact. A small-signal analysis determines the characteristic time constants for these processes, which are typically ∼1 sec. Calculated examples of the recombination and ionization coefficients, dc I-V curves, differential equation flow diagrams, and transient response are presented for parameters typical of p-type Ge photoconductors doped with shallow acceptor levels, and suggestions for the design of more stable photoconductors are presented.}, Doi = {10.1063/1.334822}, Key = {Westervelt85} } @booklet{Teitsworth84, Author = {Teitsworth, SW and Westervelt, RM}, Title = {Chaos and broadband noise in extrinsic photoconductors}, Journal = {Physical Review Letters}, Volume = {53}, Number = {27}, Pages = {2587-2590}, Year = {1984}, ISSN = {0031-9007}, url = {http://dx.doi.org/10.1103/PhysRevLett.53.2587}, Abstract = {A simple model is studied describing low-temperature free-carrier dynamics in extrinsic photoconductors due to capture by impurity atoms and impact ionization. Numerical results are presented which exhibit period doubling, chaotic behavior, and elevated effective noise temperatures. Photoconductor properties necessary for chaotic behavior are discussed. © 1984 The American Physical Society.}, Doi = {10.1103/PhysRevLett.53.2587}, Key = {Teitsworth84} } @booklet{Teitsworth83, Author = {Teitsworth, SW and Westervelt, RM and Haller, EE}, Title = {Nonlinear oscillations and chaos in electrical breakdown in Ge}, Journal = {Physical Review Letters}, Volume = {51}, Number = {9}, Pages = {825-828}, Year = {1983}, ISSN = {0031-9007}, url = {http://dx.doi.org/10.1103/PhysRevLett.51.825}, Abstract = {Self-generated nonlinear oscillations and chaos are found in the conductance of liquid-He-cooled far-infrared photoconductors made from ultrapure Ge. Complex behavior includes a period-doubling cascade to chaotic oscillation with increasing applied electric field, quasiperiodic oscillation, frequency locking, and intermittent switching between modes of oscillation. A rate-equation model is presented which includes impurity impact ionization and space-charge injection. © 1983 The American Physical Society.}, Doi = {10.1103/PhysRevLett.51.825}, Key = {Teitsworth83} } %% Preprints @article{fds199873, Author = {M. Heymann and S. W. Teitsworth and J. Mattingly}, Title = {Rare transition events in non-equilibrium systems with state-dependent noise: application to stochastic current switching in semiconductor superlattices}, Year = {2012}, Abstract = {Using recent mathematical advances, a geometric approach to rare noise-driven transition events in nonequilibrium systems is given, and an algorithm for computing the maximum likelihood transition curve is generalized to the case of state-dependent noise. It is applied to a model of electronic transport in semiconductor superlattices to investigate transitions between metastable electric field distributions. When the applied voltage V is varied near a saddle-node bifurcation at Vth , the mean life time T of the initial metastable state is shown to scale like log T \propto |Vth − V |^{3/2}.}, Key = {fds199873} }