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Low-dimensional Electron Systems Lab. (LESL)

RESEARCH

RESEARCH

SEMICONDUCTOR MATERIALS PHYSICS
& NANOSTRUCTURE ELECTRON DEVICE APPLICATIONS

  • Electrical Characterization of High-mobility Emerging Semiconductors
    (currently by YiTaek, Sanghyun, and Yongwook):
    • Transport spectroscopy; measurements of band structure information
    • Electron transport and quantum phenomena in semiconductor nanostructures
  • Vertical Electron Transport in Heterostructures Based on Van Der Waals Materials
    (currently by Sanghyun and Sanghoo):
    • Dynamic modulation of band alignment and tunneling properties
    • Ballistic transport along the vertical direction in van der Waals materials
    • Band modulation by Morie-induced superlattices
  • Nanostructure Electronic/Optoelectronic Device Applications
    (currently by Hanbyeol, Sanghoo, and Donghyeon):
    • High-performance field effect transistors
    • Multi-valued logic devices
    • Low power tunneling transistors
    • Diodes, negative differential resistors, inverters
    • IR, Vis light detectors
    • Contact property optimization etc.

TRANSPORT SPECTROSCOPY:

We have a special technique to measure electron energy (Fermi energy) as a function of electron density. The measured electron energy vs density data provide band gap, effective mass, and Fermi velocity, which are important fundamental electronic properties and critical to design of diverse electronic and optical applications. We also do manipulating electronic structure of materials for practical purposes, and probing the reconstructed electronic structure.

NOVEL QUANTUM STATES:

We are interested in various quantum phenomena such as quantum Hall effect and topological/quantum spin Hall states in two-dimensional materials. In such nanoscale materials due to the reduced dimensionality quantum effect can be pronounced. Using our non-local Fermi energy measurement technique we are capable of direct probing of energy of such quantum states. We design novel condensed matter systems, study new quantum phenomena, and explore practical nanoelectronics using emerging nanoscale materials and physics. This research includes developing new method of nano fabrication and precise characterization techniques.

QUANTUM TUNNELING and TUNNELING ELECTRONICS:

Two-dimensional (van der Waals) materials allow us to develop atomically thin nano devices, in contrast to conventional bulk materials. There are diverse choices of two-dimensional materials and their combinations, which can offer multiple functionalities. Double layer electron systems separated by an atomically thin barrier can show a variety of interesting physical phenomena including resonant quantum tunneling and unique interlayer interaction effects. We are developing new types of low-power high-speed nanoscale tunneling devices.

ELECTRON OPTICS:

In high quality graphene electrons are able to move tens of micrometers coherently without any scattering, phenomenon called ballistic transport. Electrons, as like light, then transport straight in a medium, refract at the interface where the carrier type is changed, and also can interact with other coherent electron waves. We are interested in playing with phase coherent electron waves, and developing a smart design to control electron waves effectively and substantially.

DYNAMICALLY TUNABLE PLASMONICS:

Plasmons are collective charge density oscillations in (conventionally) metals in response to incident electromagnetic field (light). Electrically tunable plasmonics is obviously more favorable then static devices. However, it cannot be easily achieved because most of conventional plasmonic materials are noble metals, of which Fermi energy is barely adjustable. In contrast, Fermi energy and corresponding plasmonic behavior of graphene are tunable using electrostatic gating. Plasmonics using two-dimensional materials (especially graphene) is thus now getting attraction, but not many systems have been suggested nor thoroughly tested. We aim to create new plasmonic heterostructures based on two-dimensional materials, where we can manipulate how much and where to populate electrons, and gain a vast plasmonic tunability.

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