Cadmium Fluoride for Optics and Optoelectronics
New Prospective Materials Based on Wide-Gap Ionic Semiconductor CdF2 for Emitters, Memory Cells, and Holographic Elements
Tech Area / Field
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Lapidus O V
Vavilov State Optical Institute (GOI), Russia, St Petersburg
- Russian Academy of Sciences / Institute of Crystallography, Russia, Moscow\nVNIIEF, Russia, N. Novgorod reg., Sarov\nRussian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg\nInstitute of General Physics named after A.M. Prokhorov RAS, Russia, Moscow\nKurchatov Research Center, Russia, Moscow
- Waseda University, Japan, Tokyo
Project summaryWide-bandgap semiconductors are of exceptional importance for contemporary optics and optoelectronics, since the materials can be used as a basis for engineering efficient and economically feasible light emitters, lasers, displays, facilities for controlling laser radiation in the visible or ultraviolet (UV) spectral ranges, etc.
The goal of the Project is to study the fundamental properties of the novel wide-bandgap semiconductor material, cadmium fluoride (CdF2), primarily by means of dielectric, magnetic, and optical spectroscopy and to analyze its potential for engineering highly efficient light emitters, memory cells, and holographic elements.
The naturally dielectric cadmium fluoride crystal can be transformed into a semiconductor state by doping and certain thermochemical treatment. Due to the ionic mechanism of chemical bonding, the CdF2 crystal displays a 7.8eV bandgap, a record for semiconductors. This gap value is about 1.5 times larger than that in diamond (5.5eV), the widest-bandgap semiconductor among traditional semiconductor materials, and more than twice the gap value in gallium nitride (3.5eV) or zinc sulfide (3.7eV). This offers fundamental potential for application of the CdF2 crystal as a light-emitting or optically nonlinear medium, capable of operating over a wide range of wavelengths. The technological possibilities for manufacturing CdF2 crystals or layers, fairly large in size and relatively low in cost, are also of considerable importance.
The Project is aimed at studying the basic properties of CdF2 semiconductor crystals, solving the problems of technology of high-quality CdF2 crystals and ceramics, and establishing the areas of efficient practical application of the material. In the course of the Project the following problems will be solved:
determination of the real structure of CdF2 semiconductor crystals, study of electronic processes and electron-vibration coupling in the crystals, analysis of the mechanisms of interaction of the crystals with electromagnetic radiation;
development of the technology of CdF2 crystal growth, elaboration of the methods of doping and the procedures of transformation of the crystals to the semiconductor state;
search for efficient applications of the wide-bandgap CdF2 semiconductor.
The following two areas of applications will be analyzed:
use of CdF2 semiconductor crystals as bulk (3D) holographic cells, capable of working online within the time range of 1s – 1ms, particularly in instruments for holographic correction of optical images. There is no alternative to CdF2 semiconductor crystals as a dynamical 3D-holographic media in the frequency range of (100 – 103) Hz. The possible use of CdF2-based holographic cells as dynamic mirrors, switches, etc. will also be studied;
development of semiconductor light emitters, single-electron transistor structures, and memory cells. A serious impediment to the application of CdF2 crystals for these purposes is the monopolar type (n-type) of conductivity. It is proposed that this impediment will be overcome by growing p-Si/n-CdF2 structures, taking into account the compatibility of cadmium fluoride with silicon. The most important problem in this area is to realize efficient flat displays on the basis of these structures. In the course of the Project this problem will be studied first. The growth of the above structures will open the way for engineering novel, advanced, components of opto- and semiconductor electronics.
For solution of the problems posed in the Project, the collaboration of 6 institutions, whose scientific expertise and potential supplement each other, is organized. The participating institutions are: (i) State Unitary Enterprise “All-Russian Scientific Center “S.I. Vavilov State Optical Institute”; (ii) A.V. Shubnikov Institute of Crystallography of the RAS; (iii) Russian Scientific Center “Kurchatov Institute”; (iv) Russian Federal Nuclear Center - All-Russian Scientific Research Institute of Experimental Physiscs (RFNC-VNIIEF); (v) Ioffe Physico-Technical Institute of the RAS; (vi) Institute of General Physics of the RAS.
Expected Results and their Application
The Project presents an applied investigation in the field of optics and optoelectronics. The main expected results of the Project are described below.
Fundamental information will be derived on the electronic structure, electronic processes, and electron-vibration coupling in CdF2 semiconductor crystals and on the processes of interaction of doped crystals with electromagnetic radiation.
Technology will be developed for the production of initial materials and for growth of high-quality doped CdF2 crystals and p-Si/n-CdF2 semiconductor structures; the work will take advantage of the achievements of modern silicon nanotechnology.
The possible use of CdF2 crystals as media for holographic correction of optical images and for online-operating optical elements will be clarified, and model experiments will be conducted.
The possible use of semiconductor р-Si/n-CdF2 structures for realizing efficient flat displays and memory cells will be clarified. Mockup structures, to be used in such devices, will be produced.
Later, the participating institutions, in collaboration with interested companies, may take part in the development of the technology of optical or optoelectronic devices, whose prototypes will be realized in the framework of the Project.
Meeting ISTC Goals and Objectives
The Project will allow scientists and engineers, who have a knowledge of equipment for nuclear and laser arms, to change the orientation of their activity to peaceful problems. The Project will support basic and applied research for peaceful goals, promote the integration of Russian scientists into the international scientific community, contribute to the solution of domestic and international problems of high optical technologies, and will facilitate the transition to market economies, meeting the demands of modern society.