Papers by Gottfried Strasser
2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
The integration of photonic crystals (PC) and quantum-cascade lasers (QCL) can lead to a powerful... more The integration of photonic crystals (PC) and quantum-cascade lasers (QCL) can lead to a powerful set of new devices for various applications, such as multi-wavelength laser, detector arrays, on-chip integration and spectroscopy. The PCs are artificial crystals that have allowed and forbidden bands for the propagation of light. Typically PCs are built up by a regular pattern of air holes
Technical Digest. Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference
Summary form only given. Ultrafast excitation of n-doped GaAs layers leads to THz emission from c... more Summary form only given. Ultrafast excitation of n-doped GaAs layers leads to THz emission from coherent plasma oscillations. The emission frequency of this THz source is given by the simple plasma frequency formula ωp=(ne2/m*ε)1/2 where n is the number of extrinsic electrons which are confined between the surface depletion field and the GaAs substrate. The desired frequency can be controlled
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
We report second-harmonic generation in GaAs-based quantum cascade lasers due to intersubband non... more We report second-harmonic generation in GaAs-based quantum cascade lasers due to intersubband nonlinearities. Using a distributed feedback grating we obtain single-mode second-harmonic surface emission, where no fundamental light is emitted via the surface.
Proceedings of the SPIE - The International Society for Optical Engineering, 2010
We describe the design, simulation, fabrication and operation of ring cavity surface emitting las... more We describe the design, simulation, fabrication and operation of ring cavity surface emitting lasers (RCSEL) based on quantum cascade structures for the midinfrared (MIR) and terahertz (THz) spectral range. MIR RCSELs facilitate an enhancement of optical power and a reduction in threshold current density, as compared to Fabry-Perot (FP) lasers. In continuous wave operation the maximum temperature of ring based
2010 Ieee Photonics Society Winter Topicals Meeting Series, 2010
physica status solidi c, 2008
In this article, Au/titanylphthalocyanine/n‐GaAs diodes incorporating ultrathin films of the arch... more In this article, Au/titanylphthalocyanine/n‐GaAs diodes incorporating ultrathin films of the archetypal organic semiconductor titanylphthalocyanine were investigated by ballistic electron emission microscopy/spectroscopy (BEEM/S). BEEM/S measurements were used to determine the transmission of ballistic electrons through titanylphthalocyanine as a function of energy and temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica E: Low-dimensional Systems and Nanostructures, 2000
We report on the realization of electrically pumped GaAs=AlGaAs microcylinder lasers emitting at ... more We report on the realization of electrically pumped GaAs=AlGaAs microcylinder lasers emitting at = 10 m. The design and fabrication process of the special resonator shapes (circular-and stadium-like cross section) are presented. The active material is a 30 period sequence of injectors=active regions made of GaAs=AlGaAs quantum wells. Far-ÿeld characteristics of these special resonators are compared and the dependence of directionality of the emission on the deformation is investigated. The bow-tie mode can be resolved in the far-ÿeld pattern. A transition from the bow-tie to another mode with highly directional emission along the short axis of the resonators is shown for the ÿrst time. Single-mode emission is detected for 100 m diameter circular microlasers with a side mode suppression exceeding 20 dB. The maximum working temperature of the microcylinder lasers is 165 K.
Physica B: Condensed Matter, 1999
In ballistic electron emission microscopy on Au-GaAs double barrier resonant tunneling diodes, el... more In ballistic electron emission microscopy on Au-GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low e ective mass and subsequently through a low-dimensional state. Experimentally, the resonant level in the double barrier structure becomes evident as clear step in the ballistic current measured as a function of sample bias. To analyze the spectrum, an extended transfer matrix method, together with the commonly accepted Bell Kaiser model is used. In terms of this model we show that only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.
Microelectronic Engineering, 1999
In Ballistic Electron Emission Microscopy, ballistic electrons are injected from a metallic base ... more In Ballistic Electron Emission Microscopy, ballistic electrons are injected from a metallic base contact into a semiconductor. In the this experiment, the miniband of a GaAs-AlGaAs superlattice is employed as energy filter in order to study the energetic distribution of the ballistic electrons injected into the semiconductor. It is found, that due to the large difference in electron mass between Au and GaAs, parallel momentum conservation leads to considerable electron refraction at the Au-GaAs interface. Moreover, a resonant tunneling structure directly at the sample surface can act as momentum filter for electrons injected at k,,=O.
Journal of Physics: Condensed Matter, 2012
Magneto-transport measurements are performed on two-dimensional GaAs electron systems to probe th... more Magneto-transport measurements are performed on two-dimensional GaAs electron systems to probe the quantum Hall (QH) effect at low magnetic fields. Oscillations following the Shubnikov-de Haas (SdH) formula are observed in the transition from the insulator to QH liquid when the observed almost temperature-independent Hall slope indicates insignificant interaction correction. Our study shows that the existence of SdH oscillations in such a transition can be understood based on the non-interacting model.
Journal of Luminescence, 2000
We show that interaction-assisted modes of transport play a role in the energy relaxation of exci... more We show that interaction-assisted modes of transport play a role in the energy relaxation of excitons in disordered GaAs quantum wells. Semitransparent gold "lms are found to induce a blue shift in the photoluminescence spectrum of disordered wells. We interpret the result in terms of a long-range electromagnetic hopping coupling suppressed by image dipoles in the gold. The results are supported by Monte Carlo simulations of electromagnetically-assisted exciton hopping using hop rates modi"ed by the gold layer.
Journal of Crystal Growth, 2009
We present the growth and characterization of InAs quantum dots on AlxGa1−xAs surfaces for inters... more We present the growth and characterization of InAs quantum dots on AlxGa1−xAs surfaces for intersubband devices. This requires the quantum dot energy levels in the AlxGa1−xAs matrix to be above the GaAs bandedge. Using standard As4 fluxes (beam equivalent pressure 8e−6Torr), inhomogeneous broadening of the quantum dot size distribution increases with increasing Al content in the AlxGa1−xAs matrix. Reducing the
York-We investigate the THz Hall conductivity through measurement of the Faraday effect at 84 cm ... more York-We investigate the THz Hall conductivity through measurement of the Faraday effect at 84 cm −1 near the cyclotron resonance (CR) in a two dimensional electron gas formed at a GaAs/(AlGa)As interface. Motivated by predictions of novel step-like features in the optical Hall conductivity (σ xy) by Morimoto et.al. (Phys. Rev. Lett. 2009), we measure the THz σ xy as a function of filling factor and temperature using polarization modulation techniques (Grayson, Phys. Rev. Lett. 2002). We observe plateaus in the Faraday rotation near integer filling factors of 1, 2 and 3 which we attribute to the THz integer quantum Hall effect. In electron density dependent studies, we observe a slight non-monotonic shift of the plateaus as a function of filling factor at magnetic fields above CR. A comparison of this effect with the shift in temperature shows that this cannot be explained by a simple electronic heating effect. This research was funded through NSF-DMR1006078.
Form Approved OMB NO. 0704-0188 Public Reporting burden for this collection of information is est... more Form Approved OMB NO. 0704-0188 Public Reporting burden for this collection of information is estimated to aveVge 1 hour per response, including the rime for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports,
Physica E: Low-dimensional Systems and Nanostructures, 2002
ABSTRACT
Microelectronic Engineering, 1999
A systematic study of electron transport in undoped GaAs/GaAlAs superlattices is presented. Hot e... more A systematic study of electron transport in undoped GaAs/GaAlAs superlattices is presented. Hot electron spectroscopy is used to measure the superlattice transmisstance at different bias conditions. At zero bias the measured transfer ratio a=&& is used to determine the miniband positions and the miniband widths. The transmittance of a five period superlattice is found to be independent of the direction of the electric field, while for a superlattice larger than ten periods, a dependence of the transmission on the electric field direction is observed. The onset of scattering induced miniband transport is clearly evident. From the experimental data a coherence length of 150 nm is derived. The limiting mechanism is found to be interface roughness scattering.
Applied Surface Science, 1991
High-purity GaAs layers of 8 to 80 #m thickness on semi-insulating substrates have been investiga... more High-purity GaAs layers of 8 to 80 #m thickness on semi-insulating substrates have been investigated. From the ls-2p transition of shallow donors the dopants are identified and the exact transition energies determined. Using the relation Aw oc ~ from cyclotron emission measurements the total ionized impurity density N I was determined. In homogeneous samples a good agreement between the impurity density determined from the cyclotron resonance linewidth with total impurity density values obtained from Hall mobility data is found. The photoconductivity and transmission measurements show the same linewidth on impurity dependence for the different types of shallow donors.
AIP Conference Proceedings, 2011
ABSTRACT We investigated a 2 nm thin InAlN/AlN barrier after recessing of a GaN cap on top of it ... more ABSTRACT We investigated a 2 nm thin InAlN/AlN barrier after recessing of a GaN cap on top of it and Ir gate metallization. Detailed analysis of the recess process revealed practically no damage until the formation of an etch-resistant barrier layer producing nitrogen vacancies and hence defect assisted tunneling through the thin barrier. Annealing of the Ir-based gate stack showed a reduction of the electrical distance between the gate and the channel. The effect was linked to an oxygen-containing interface layer between the Ir metal and the InAlN layer where oxygen diffused into Ir at elevated temperatures. Resulting devices showed state-of-the-art normally-off performance.
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Papers by Gottfried Strasser