Ultrafast electron energy-dependent delocalization dynamics in germanium selenide

Ultrafast scattering process of high-energy carriers plays a key role in the performance of electronics and optoelectronics, and have been studied in several semiconductors. Core-hole clock spectroscopy is a unique technique for providing ultrafast charge transfer information with sub-femtosecond timescale. Here we demonstrate that germanium selenide (GeSe) semiconductor exhibits electronic states-dependent charge delocalization time by resonant photo exciting the core electrons to different final states using hard-x-ray photoemission spectroscopy. Thanks to the experiment geometry and the different orbital polarizations in the conduction band, the delocalization time of electron in high energy electronic state probed from Se 1s is ~470 as, which is three times longer than the delocalization time of electrons located in lower energy electronic state probed from Ge 1s. Our demonstration in GeSe offers an opportunity to precisely distinguish the energy-dependent dynamics in layered semiconductor, and will pave the way to design the ultrafast devices in the future.

Radiative recombination and other processes related to excess charge carriers, decisive for efficient performance of electronic devices

We present selected semiconductor (inorganic and organic) structures for which non-radiative recombination of excess charge carriers is very high, luminescence suppressed and its lifetime substantially shortened. Processes competitive with radiative energy emission are discussed. The importance of Shockley–Read–Hall recombination in materials with high impurity or defect concentration, applied in ultrafast devices, is shown. Also, charge transfer process in solar cells is discussed in the context of luminescence quenching of individual components of an active layer. A part of the shown research was a subject of our common work with Prof. Arūnas Krotkus during the period from 1994 till 2006.

Resonators induced transparency and optical switching assisted by optofluidic pump system

A tunable plasmonic induced transparency (PIT)-based light switching is proposed and investigated. The proposed structure consists of a bus waveguide, two nanoresonators and an optofluidic pump system for actively tuning the system’s transmission. By using the finite difference time domain method, it is found that the interferences between the dark and bright mode resonators can be controlled by manipulating the fluid filled in the resonator, leading to an actively tunable plasmonic switch, the transmittance can be flexibly tuned from near unity to zero. The structure in our paper has the following advantages, such as ultracompact size and easy fabrication. Our study will provide a possibility for designing the ultrafast devices in highly integrated optical circuits.