In-plane surface plasmonics integrated with THz Quantum cascade lasers for high collimation

We report planar integration of tapered Terahertz (THz) quantum cascade lasers (QCLs) with spoof surface plasmon (SSP) structures. The SSP structure consists of one plasmonic coupler and periodically arranged scatters. The resulting surface-emitting THz beam is highly collimated with a beam divergence as narrow as 3.6°×9.7°. As the beam divergence is inverse proportional to the light emission area, this low divergence indicates a good waveguiding property of the SSP structure, while the low optical background of the beam implies a high coupling efficiency of the THz wave from the laser cavity to the SSPs. Since all the structures are in-plane, this scheme provides a promising platform where the well-established SP techniques can be employed to engineer the THz QCL beam with high flexibilities

Growth of Low-Density Vertical Quantum Dot Molecules with Control in Energy Emission

In this work, we present results on the formation of vertical molecule structures formed by two vertically aligned InAs quantum dots (QD) in which a deliberate control of energy emission is achieved. The emission energy of the first layer of QD forming the molecule can be tuned by the deposition of controlled amounts of InAs at a nanohole template formed by GaAs droplet epitaxy. The QD of the second layer are formed directly on top of the buried ones by a strain-driven process. In this way, either symmetric or asymmetric vertically coupled structures can be obtained. As a characteristic when using a droplet epitaxy patterning process, the density of quantum dot molecules finally obtained is low enough (2 × 108 cm−2) to permit their integration as active elements in advanced photonic devices where spectroscopic studies at the single nanostructure level are required

Patterning the second-order optical nonlinearity of asymmetric quantum wells by ion implantation enhanced intermixing

The change in the second-order nonlinear susceptibility of an asymmetric quantum well (AQW) superlattice induced by ion beam-enhanced intermixing has been measured. The surface-emitted second-harmonic intensities radiated from implanted and masked areas of an AQW waveguide were measured and compared for incident wavelengths between = 1480 and 1600 nm. Intermixing resulted in a 60 meV blueshift of the AQW band edge and a uniform suppression of the AQW second-order susceptibility, while the masked AQWs were unchanged

Self-organized quantum rings:physical characterization and theoretical modeling

\u3cp\u3eAn adequate modeling of self-organized quantum rings is possible only on the basis of the modern characterization of those nanostructures. We discuss an atomic-scale analysis of the indium distribution in self-organized InGaAs quantum rings (QRs). The analysis of the shape, size and composition of self-organized InGaAs QRs at the atomic scale reveals that AFM only shows the material coming out of the QDs during the QR formation. The remaining QD material, as observed by Cross-Sectional Scanning Tunneling Microscopy (X-STM), shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and determines the observed ring-like electronic properties of QR structures. A theoretical model of the geometry and materials properties of the self-organized QRs is developed on that basis and the magnetization is calculated as a function of the applied magnetic field. Although the real QR shape differs strongly from an idealized circular-symmetric open-ring structure, Aharonov-Bohm-type oscillations in the magnetization have been predicted to survive. They have been observed using the torsion magnetometry on InGaAs QRs. Large magnetic moments of QRs are shown to originate from dissipationless circulating currents in the ground state of an electron or hole in the QR. Examples of prospective applications of QRs are presented that do and do not utilize the topological properties of QRs.\u3c/p\u3