PD Dr. techn. Gregor Koblmüller

Telefon
+49 89 289-12779
Raum
E-Mail
gregor.koblmueller@tum.de
Links
Visitenkarte in TUMonline
Arbeitsgruppen
Fakultät für Physik
Halbleiter-Nanostrukturen und -Quantensysteme
Funktion
Privatdozent am Physik-Department

Lehrveranstaltungen und Termine

Ausgeschriebene Angebote für Abschlussarbeiten

Characterization of doped GaAs-AlGaAs core-multishell nanowire lasers

Semiconductor nanowires (NW) are rapidly emerging as a new generation of miniaturized on-chip coherent light sources by virtue of their unique geometry. In particular, as they represent natural Fabry-Perot resonators, combined with the possibilities for direct monolithic integration on Si, NW lasers offer attractive applications in future optical interconnects and data communication.

While up to date these NW lasers are driven optically, an electrical operation of these devices is necessary for all applications. For this purpose, precise control of the doping, the development of electrical contacts, and a sophisticated mirror concept in the device are required.

The aim of this project is to explore n- and p-type doping and develop appropriate process technologies for contacting doped core-multishell NWs in different device geometries. This will allow the characterization of the devices with respect to their electrical and optoelectronic properties. Moreover, a comprehensive 2D-3D TCAD model of the NW laser will be implemented to simulate the electro-thermal performance of the device. Adjusting the simulations to the measurement results will enable the optimization of the doping profile and the heterostructure design of the NW laser. In the second part of the project, different mirror concepts will be simulated and fabricated on a freestanding NW geometry and finally characterized by optical measurements.

As a highly motivated M.Sc. student you will be closely interacting with several other student members within the Nanowire Group at the Walter Schottky Institut (WSI), and you will learn a wide scope of semiconductor-based preparation and physical characterization methods and technologies. Experience in the area of clean room fabrication or TCAD modeling are a benefit, but secondary to motivation and commitment. Applications should be sent to Jochen.Bissinger@wsi.tum.de or PD Dr. Gregor Koblmueller (Gregor.Koblmueller@wsi.tum.de). Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

geeignet als
  • Masterarbeit Physik der kondensierten Materie
  • Masterarbeit Applied and Engineering Physics
Themensteller(in): Gregor Koblmüller
Development of InGaAs-based nanowire lasers for Si photonics

At the Walter Schottky Institut we have recently gained great expertise in exploring nanowire (NW) lasers as the smallest possible semiconductor-based coherent light sources. One of their most promising features is that they can be also integrated onto silicon (Si) platform and thereby provide a nanoscale source for potential operation in Si photonic circuits.

An important step forward towards integration into Si photonic circuits is to control the emission wavelength of the nanowire laser in the technologically relevant spectral range of 1.3 – 1.55 um. For this reason it is necessary to develop new active gain materials in III-V based nanowire lasers, such as InGaAs multi-quantum well structures inside NW Fabry-Perot resonator cavities, and integrate these onto Si-based ridge waveguides.

The aim of this project is to develop long-wavelength InGaAs-based quantum wells incorporated in GaAs-based resonator cavities using sophisticated nanofabrication and characterization methodologies. Interacting closely with a PhD student you will be designing and synthesizing these laser structures using molecular beam epitaxy, and then characterizing their laser metrics by confocal micro-photoluminescence spectroscopy (uPL). The design and characterization may also be supported by state-of-the-art simulations of the laser gain spectrum and optical waveguiding properties. Ultimately, the InGaAs-based NW lasers should be integrated directly onto Si-ridge waveguides. Here, you will be actively exploiting various semiconductor processing techniques to fabricate the desired templates for direct monolithic integration. The coupling and lasing mode propagation between NW laser and Si waveguide will then be investigated by two-axis uPL experiments.

In this thesis, you will be closely working with several other student members in the Nanowire Group at WSI, led by PD. Dr. Gregor Koblmueller. Experience in the area of clean room fabrication or optical spectroscopy is a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de or Jochen.Bissinger@wsi.tum.de. Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

geeignet als
  • Masterarbeit Physik der kondensierten Materie
  • Masterarbeit Applied and Engineering Physics
Themensteller(in): Gregor Koblmüller
Fabrication and electrical characterization of high-mobility nanowire field effect transistor devices

At the Walter Schottky Institute we have an ongoing research program on the growth and nano­fabrication of high mobility III-V semiconductor based heterostructure nanowire FET devices. One of the possible applications of such small devices is their integration onto CMOS-compatible silicon platform and thereby pave the way for next generation ultrascaled nanoelectronic switches in future consumer electronics.

An important step towards high mobility nanowire-FET devices is a very good understanding of the charge carrier scattering processes due to impurities, crystal phase intermixing, alloy fluctuations and surface effects among others, which limit the mean free path. Such understanding may then provide routes towards resistance-less ballistic FETs, devices which ideally occur in 1D-like conductors such as nanowires.

The goal of this project is to explore the novel InAs/InAlAs nanowire material system towards the ballistic transport regime in a temperature range between 2K and 300K. Interacting closely with a PhD student you will be designing transistor structures for direct synthesis which you will thereafter fabricate into working FET devices. Hereby, you will utilize our state-of-the-art cleanroom facilities using a variety of techniques, including optical and electron beam lithography. The FET devices should be optimized with respect to their size (nanowire diameter), carrier density and channel length in order to access regimes for ballistic transport. The nanowire-FET measurements will then be performed at a dedicated low-noise temperature-dependent electrical transport setup, and the results compared with simulations of the transmission of charge carriers in a 1D-conductor.

In this thesis, you will be closely working with several other student members in the Nanowire Group at WSI, led by PD Dr. Gregor Koblmueller. Experience in the area of clean room fabrication or (nano)electronics, as well as experience using Matlab is a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de or Jonathan.Becker@wsi.tum.de . Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

geeignet als
  • Masterarbeit Physik der kondensierten Materie
  • Masterarbeit Applied and Engineering Physics
Themensteller(in): Gregor Koblmüller
Synthesis and characterization of novel 2D-materials heterostructures

Layered materials have been at the center of attention since the discovery of graphene as they hold great promise for uncovering new physical phenomena and for creating new applications. Transition metal dichalcogenides (TMDCs) are such materials systems possessing a wide range of energy bandgaps and band alignments which can be tuned by layer thickness and engineering the dielectric environment.

While most of the 2D-layered materials are harvested by simple exfoliation techniques,there is currently a huge desire to prepare these materials by scalable synthesis methods which should produce high-quality wafer-scale 2D crystals with tunable properties.

The aim of this project is to exploit chemical vapor deposition (CVD) as a scalable synthesis method to create van der Waals (vdW) bonded atomically thin TMDC crystals and heterostructures, primarily from the (Mo,W)S2 family of materials. Hereby, a wide spectrum of the synthesis parameters should be explored to tune the growth kinetics and thermodynamics leading to different crystal domain shapes, sizes and orientations on different substrates. A major goal should be the demonstration of heterostructure formation between MoS2/WS2 layers as well as their embedment into h-BN (hexagonal boron nitride) to engineer the interface properties that can host new types of high-efficiency quantum emitters. A wide range of complementary nano-analytical methods is available to further investigate the structure-property function relationships, including Raman and photoluminescence spectroscopy as well as advanced microscopy methods (SEM, He-Ion Microscopy).

In this thesis, you will be closely working with other student members active in 2D-Materials Research at the WSI. Experience in the area of clean room fabrication, chemistry, or optical spectroscopy is a benefit, but secondary to motivation and commitment. Applications should be sent directly to Gregor.Koblmueller@wsi.tum.de. Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

geeignet als
  • Masterarbeit Physik der kondensierten Materie
  • Masterarbeit Applied and Engineering Physics
Themensteller(in): Gregor Koblmüller

Kondensierte Materie

Wenn Atome sich zusammen tun, wird es interessant: Grundlagenforschung an Festkörperelementen, Nanostrukturen und neuen Materialien mit überraschenden Eigenschaften treffen auf innovative Anwendungen.

Kern-, Teilchen-, Astrophysik

Ziel der Forschung ist das Verständnis unserer Welt auf subatomarem Niveau, von den Atomkernen im Zentrum der Atome bis hin zu den elementarsten Bausteinen unserer Welt.

Biophysik

Biologische Systeme, vom Protein bis hin zu lebenden Zellen und deren Verbänden, gehorchen physikalischen Prinzipien. Unser Forschungsbereich Biophysik ist deutschlandweit einer der größten Zusammenschlüsse in diesem Bereich.