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Nanotechnology and nanoscale materials and devices exhibit fascinating prospects for innovations in the 21th century. Ultra thin layers or tiny crystals show unusual properties which can be tailored in a controlled way to match the requirements for new electronic applications. Within this promising research field, the design of nanoscale materials, structures and devices as well as their microscopic understanding are key issues. Applications in micro- or optoelectronics are more and more dominated by nanostructures. In addition, also completely new research fields, like, e.g., spintronics (the use of the spin degree of freedom as an information carrier in semiconductors) or quantum information technology (the use of quantum mechanical properties for information processing) have emerged.
Within this field, the research activities at the chair of electronic materials and nanostructures can be divided into 3 areas:
Functional and Failure Analysis of Micro- and Optoelectronic Devices
Modern micro- and optoelectronic devices contain functional layers and structures with characteristic sizes down to the Sub-100 nm range. Therefore, experimental techniques are required that allow for probing current flows and potential distributions on a nanometer scale.
Using different scanning probe techniques (e.g., Kelvin force microscopy, conductive atomic force microscopy, current/voltage contrast measurements) we investigate the local potential drop as well as the local current flow in light emitting diodes, laser diodes and microelectronic circuits. In addition, innovative nanoscale devices such as nanoparticle sensors or nanowhisker LEDs are studied. Using suitable preparation and measurement techniques we are able to determine vertical as well as lateral current and voltage distributions with a spatial resolution on the order of a few tens of nanometers. The well-established techniques of high resolution electron microscopy and spatially and time-resolved optical spectroscopy contribute to a comprehensive analysis by revealing structural and optical properties of the devices.
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Completed projects
Nano-Optoelectronics and Quantum Information Technology
By decreasing the size of semiconductor crystals in all three dimensions down to a few nanometers, one obtains quantum dots with properties that have to be described quantum mechanically. The discrete energy level structure, which can be adjusted simply by varying the quantum dot size, and the modified density of states open fascinating aspects for innovative applications. Light emitting devices with tailored wavelengths and laser diodes with reduced threshold can be realized, as well as quantum dot based devices which are able to deliver single photons ‘on demand’ or to store single electrons. Device concepts based on single electrons, photons or spins are the basis for a new kind of information technique, the ‘quantum information technology’. Here, quantum mechanical properties, like, e.g. the spin of an electron, are used to represent an information unit.
Using high resolution (transmission) electron microscopy, time- and spatially resolved optical spectroscopy and scanning probe techniques we investigate semiconductor quantum objects, like single or coupled quantum dots or nanoparticles. In our cleanroom (class 100) we develop device concepts for optoelelectronic applications and quantum information technology. Current topics of interest are single spin memories and single photon sources based on epitaxially grown quantum dot heterostructures, and nanoparticle based light emitters for printable optoelectronics.
Recent publications
Current projects
Completed projects
Hybrid Materials for Spintronics
In conventional microelectronics, the charge of electrons is used as an information carrier. An innovative concept in information technology is based on the idea of using the quantum mechanical property ‘spin’ of a charge carrier for representing information units. The carrier spin is already used in read heads of modern hard disks: In nanometer-thin ferromagnet-isolator layer sequences the current flow depends on the relative orientation between the carrier spins and the magnetization of the ferromagnet.
‘Spintronics’ (in a narrower sense) describes the usage of the carrier spins in semiconductors, which allows one to envision completely new device concepts. Central issues are spin injection into semiconductors as well as spin lifetimes and spin coherence times, spin transport and spin manipulation in semiconductors.
We work on new materials and material combinations with the focus on concepts for local spin manipulation in semiconductors. In magnetically doped quantum dots and nanoparticles we study the local interaction between carrier spins and magnetic impurities. In addition, we develop nanoscale ferromagnet-semiconductor hybrids in order to locally manipulate incoherent or coherent spin states in a semiconductor via the magnetic fringe fields. Alternatively, local magnetic fields are generated by microscopic coils, which enable us to switch spin states electrically. The research activities require an intense interaction between sample development by electron beam lithography in our clean room and analysis using modern techniques of time- and spatially resolved magneto-optics.
Recent publications
Current projects
Completed projects
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