Zhihuan Wang

Opto-plasmonic devices: controlling light with electrons

We investigate mechanisms by which interaction of light and matter may be affected by electrons, and show how this can lead to optoelectronic devices with superior properties. In particular, confined cloud of electron gas allows sculpting a wave function that affects both emission and absorption of radiation, while its collective, plasmonic, excitation may be used for optical wave guiding, coupling and radiation. Such processes require much less energy and are much faster than classical kinetic energy-based charge transport in traditional electronics. Here we present thin-film photodetectors in which 2D electron and hole charges allow operation in hundreds of GHz, without applied bias, requiring a fraction of microwatt of optical power. The 2D channel can also be structured to provide the momentum change that is required for coupling to excitation at THz range. The confined charge is then used as a plate of (an unconventional) capacitor which changes states by a factor of >1000, in tens of fs, requiring atto-joules of energy which is also switchable by light. This opto-plasmonic capacitor finds application in threshold logic based neuromorphic systems. These thin-film devices are produced in bottom-up core-shell nanowire (CSNW) technology, resulting in resonant optical cavities whose properties are controlled by 2D and 1D charge plasma, with orders of magnitude increase in absorption and emission of light that leads to lasing at room temperature even without vertical structure. Since CSNWs can be grown on Si, they can be good candidate platforms for Photonic Integrated Circuits (PIC) and Silicon Photonics.

Light and Rate Management in Nanowires

We analyze optoelectronic properties of core-shell nanowires explaining how both light management and transition rate management need to be included in order to explain their extraordinary absorption and emission properties.