Doctoral College TU-D Unravelling advanced 2D materials
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Nanoscale device physics and technology

Thomas Müller, Graphenelabs

Research in the TM group focuses on the fabrication and characterization of electronic and optoelectronic devices based on two-dimensional (2D) materials, such as graphene and monolayer semiconductors, and 2D heterostructures. The group has excellent expertise and strong record in 2D materials transfer and nanodevice fabrication, and has made internationally recognized contributions on the electronic and optical properties of graphene and other 2D materials. Highlights include early photoconductivity studies of graphene and development of the first ultrafast graphene-based photodetectors [TM 1], integration of graphene into silicon chips for photonic integrated circuits [TM 2], demonstration of electrically driven light emission in an atomic monolayer p-n diode [TM 3], application of van der Waals heterostructures in photovoltaics [TM 4], and photoconductivity studies of 2D semiconductors [TM5].

PhD Project 1: Single photon light emitting diodes based on 2D materials

Co-supervisor: Peter Blaha

Goal of this project is the design and fabrication of an electrically driven single-photon source based on trap states in atomically thin transition metal dichalcogenides (TMDs). To obtain material of highest quality, TMD monolayer will be grown by CVD in house. Electrical devices will be fabricated via electron-beam lithography, deposition and etching techniques. An optimized outcoupling of the single-photon emission from the TMD monolayers is provided by nanophotonic structures, such as plasmonic nanoantennas or dielectric resonators. Photon statistics measurements will be performed. The fabricated single-photon sources are modeled by a microscopic theory to understand the electronic structure and origin of trap states in TMDs and optimize the device performance. The student will become familiar with state-of-the-art nanoscale device fabrication technologies, design of nanophotonic structures, CVD growth of nanomaterials, optical techniques for single photon emission characterization, and first-principle calculations of the electronic structure of trap states in TMDs. Theoretical aspects of this work will be co-supervised by Peter Blaha

PhD Project 2: Photodetectors based on 2D materials and heterostructures

Co-supervisor: Florian Libisch

In this project we will work with individual 2D materials (e.g. WSe2) and heterostructures of different 2D materials (e.g. graphene/WSe2/graphene heterojunctions) to realize novel photodetectors. The work involves the fabrication of test structure devices and the optical and electro-optical characterization of these devices in order to understand the different mechanisms for photocurrent generation, that govern light induced carrier interactions, exciton dynamics, phonon-electron coupling, charge transfer, plasmons and energy transfer. This work will involve state-of-the-art spectroscopic techniques at different wavelengths, including scanning photocurrent microscopy and time resolved photocurrent spectroscopy. The student will (i) gain detailed knowledge on photodetection mechanisms in new layered materials and heterostructures and identification of the key parameters defining and limiting their performance; (ii) exploit the light-induced charge carrier dynamics to tailor photodetection and photoconversion devices. This project will be co-supervised by Florian Libisch, who will guide the student in in theoretical aspects of this work.


Literature

  1. T. Mueller, F. Xia, Ph. Avouris: Graphene photodetectors for high-speed optical communications. Nature Photonics 4, 297 (2010) DOI: 10.1038/nphoton.2010.40
  2. A. Pospischil, et al.: CMOS-compatible graphene photodetector covering all optical communication bands. Nature Photonics 7, 892 (2013) DOI: 10.1038/nphoton.2013.240
  3. A. Pospischil, M.M. Furchi, T. Mueller. Solar-energy conversion and light emission in an atomic monolayer p-n diode. Nature Nanotechnology 9, 257 (2014) DOI: 10.1038/nnano.2014.14
  4. M. Furchi, A. Posposchil, F. Libisch, J. Burgdörfer, and T. Müller. Photovoltaic effect in an electrically tunable van der Waals heterojunction. Nano Letters 14, 4785 (2014) DOI:  10.1021/nl501962c
  5. M. Furchi, D. Polyushkin, A. Pospischil, T. Mueller: Mechanisms of photoconductivity in atomically thin MoS2; Nano Letters 14, 6165 (2014) DOI: 10.1021/nl502339q