1,077 research outputs found
Exciton-photon interactions in semiconductor nanocrystals: Radiative rransitions, non-radiative processes and environment effects
In this review, we discuss several fundamental processes taking place in semiconductor nanocrystals (quantum dots (QDs)) when their electron subsystem interacts with electromagnetic (EM) radiation. The physical phenomena of light emission and EM energy transfer from a QD exciton to other electronic systems such as neighbouring nanocrystals and polarisable 3D (semi-infinite dielectric or metal) and 2D (graphene) materials are considered. In particular, emission decay and FRET rates near a plane interface between two dielectrics or a dielectric and a metal are discussed and their dependence upon relevant parameters is demonstrated. The cases of direct (II–VI) and indirect (silicon) band gap semiconductors are compared. We cover the relevant non-radiative mechanisms such as the Auger process, electron capture on dangling bonds and interaction with phonons. Some further effects, such as multiple exciton generation, are also discussed. The emphasis is on explaining the underlying physics and illustrating it with calculated and experimental results in a comprehensive, tutorial manner.Funding from the Ministry of Science and Higher Education of the Russian Federation (State Assignment No 0729-2020-0058), the European Commission within the project "GrapheneDriven Revolutions in ICT and Beyond" (Ref. No. 696656), from the Portuguese Foundation for Science and Technology (FCT) in the framework of the PTDC/NAN-OPT/29265/2017 "Towards high speed optical devices by exploiting the unique electronic properties of engineered 2D materials" project and the Strategic Funding UID/FIS/04650/2019 is gratefully acknowledged
Optical and electrical properties of undoped and doped Ge nanocrystals
Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate
Structure and Spatial Distribution of Ge Nanocrystals Subjected to Fast Neutron Irradiation
The influence of fast neutron irradiation on the
structure and spatial distribution of Ge nanocrystals (NC)
embedded in an amorphous SiO2 matrix has been
studied. The investigation was conducted by means of
laser Raman Scattering (RS), High Resolution
Transmission Electron Microscopy (HR-TEM) and X-ray
photoelectron spectroscopy (XPS). The irradiation of GeNC samples by a high dose of fast neutrons lead to a
partial destruction of the nanocrystals. Full reconstruction
of crystallinity was achieved after annealing the radiation
damage at 800
0
C, which resulted in full restoration of the
RS spectrum. HR-TEM images show, however, that the
spatial distributions of Ge-NC changed as a result of
irradiation and annealing. A sharp decrease in NC
distribution towards the SiO2 surface has been observed.
This was accompanied by XPS detection of Ge oxides and
elemental Ge within both the surface and subsurface
regio
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