Dr. Akhil Ajay

Offered Bachelor’s or Master’s Theses Topics

Selten-Erd Photoleiter zur Erzeugung und Detektion von Terahertz Strahlung

Terahertz (100 GHz - 10 THz) devices experience a fast growth of interest in recent years, where photonic systems (such as photomixers) are on the horizon to soon enable commercial or industrial THz applications. The operation of photonic systems relies, principally, on the excitation of a photoconductive material by e.g. a pulsed laser with a pulse duration much shorter that 1 ps = 1 THz-1 (typically < 100 fs). Thereby, the photoconductive material (a highly resistive semiconductor) is switched by the laser pulse to a conductive state by generating electron-hole pairs via absorption, while an applied DC bias further separates the carriers, giving rise to a current containing THz frequency components. So far, the major bottleneck hindering desired performance metrics, was the photoconductive material itself. The material needs to fulfill numerous requirements, such as e.g. high absorption coefficient at the technologically relevant 1.55 µm wavelength range, sub-ps carrier life¬time, high carrier mobility, high breakdown field strength and high resistance (low dark current). Therefore, major research efforts are needed to develop new photoconductor materials and bring such photonic systems out of basic research to real-life commercial applications. Goal of Thesis: The aim of this thesis is to develop ultrafast photoconductor materials with small band gap suitable for laser and fiber technology at 1.55 µm. In particular, we will focus on InGaAs-based materials and superlattices doped with self-assembled rare-earth (ErAs, ErSb) precipitates, which act as efficient trap sites to tune carrier lifetime while maintaining high carrier mobility. This prototype system should further allow exceptional control of carrier capture and resistance by p-compensation doping and As/Sb-alloying strategies. Thereby, you will work closely with team members of the SQNM group to learn and develop numerous methods in • the epitaxial synthesis of metal/semiconductor systems (molecular beam epitaxy) • state-of-the-art characterization of structural properties (high-resolution X-ray diffraction, TEM, He-ion microscopy, AFM) • advanced carrier transport & optical spectroscopy (Hall-effect probe, PL) Good knowledge in physics, semiconductors, as well as previous experience with lab work related to characterization of semiconductors are a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de or Akhil.Ajay@wsi.tum.de. Please include your CV, and a transcript of records (Bachelor & Master). Last date: 15 October 2021

suitable as

• Master’s Thesis Applied and Engineering Physics

Supervisor: Gregor Koblmüller