It was also shown that the long-term ordered and therefore close-to-ideal crystals demonstrate bright luminescence and stimulated emission repeating behavior of the best nanoparticles with pronounced quantum confinement effects. Therefore, there are only two ways of preparing a material with bright luminescence from IR to UV regions: to prepare very perfect, defectless single crystals or nanocrystals with the dimensions less than electron-hole free path in this material of standard quality.
Correctness of the chosen way can be confirmed by the following comparison of optical properties of the best GaP nanocrystals and GaP perfect bulk single crystals. Jointly with the references [ 3 , 7 , 9 - 17 , 21 - 27 , 32 ] here we present a generalization of the results on long-term observation of luminescence, absorption, and Raman light scattering in bulk semiconductors in comparison with some properties of the best to the moment GaP nanocrystals.
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The combination of these characterization techniques elucidates the evolution of these crystals over the course of many years, the ordered state brought about by prolonged room-temperature thermal annealing, and the interesting optical properties that accompany such ordering. We demonstrate that long-term natural stimuli improve the perfection of our crystals, which can lead to novel heterogeneous systems and new semiconductor devices with high temporal stability.
Raman light scattering confirms high quality of the long-term ordered crystals. Nanoparticles were prepared from white P by mild aqueous or colloidal synthesis at decreased temperature, stored as the dry powder spectrum 2 or suspension in a liquid spectrum 3. Details: [15, 17]. We further improved upon the preparation of GaP nanocrystals using the known methods of hydrothermal and colloidal synthesis [ 30 - 32 ] by taking into account that the success of our activity depends on the optimal choice of the types of chemical reactions, necessary chemicals and their purity, conditions of the synthesis control accuracy, temperature, pressure, duration, etc.
The best quality GaP nanoparticles have been prepared by hydrothermal or colloidal synthesis from white phosphorus at decreased temperature o C and intense ultrasonication; it was established that the maximum shift of their luminescence to ultraviolet and the best quality in general have the nanocomposites obtained from the nanoparticles of the same dimensions stored as a suspension in a suitable liquid.
Nanocrystals of the different dimensions, stored as dry powder, demonstrate rather broad luminescent band with maximum at 2. The thoroughly washed, ultrasonicated and dried nanopowders as well as their specially prepared suspensions have been used for fabrication of blue light emissive GaP nanocomposites on the base of some optically and mechanically compatible with GaP polymers [ 15 , 17 , 30 - 32 ]. Long-term ordering leads to the creation of perfect bulk GaP crystals with considerably expanded and bright emissive band, practically the same as in the perfect GaP nanoparticles.
We explain the broadening of the luminescence band and the shift of its maximum to low photon energies in luminescence of the nanocomposite based on the GaP powder by presence in the powder of the nanoparticles with the different dimensions between 10 and nm. Meanwhile, the nanocomposites on the base of the suspensions containing only approximately 10 nm nanoparticles exhibit bright luminescence with a maximum at 3. In accord with our data [ 15 , 31 ] the shift due to the quantum confinement effects is about a few tenths of eV and, obviously, it is impossible to explain only through this effect the dramatic 1 eV expansion of the region of luminescence at K to the high-energy side of the spectrum.
Taking into account the high light absorption coefficient equal to approximately 10 5 cm -1 for photons with the energy in the vicinity of maximum at 3. Really, a big GaP single crystal, even very perfect one, in principle, cannot emit many photons in UV region, because the overwhelming majority of those photons will be immediately absorbed in the crystal; only tiny defectless 10 nm GaP spheres, transparent for this UV region, distributed in the transparent suspension or a polymer film will easily emit this UV light.
Note, our first attempts to prepare GaP nanoparticles [ 18 , 28 ] yielded room temperature luminescence with the maximum shifted only to 2. The perfect quality of the nanoparticles prepared by improved technologies is confirmed by all the used methods of characterization, while investigation of Raman light scattering evolution during 25 years since clear confirms considerable improvement of GaP single crystal quality and the existence of new interesting phenomena characterizing only very perfect crystals.
Besides that, using all the noted in the presented review opportunities, including specially doped GaP and the necessary level of luminescence excitation, we can change the position of maximum and bandwidth of luminescence in wide, from infrared 1. The role and application of bound excitons in nanoscience and technology are discussed in this chapter. Bound excitons are well studied in semiconductors, especially in gallium phosphide doped by nitrogen GaP:N [ 3 , 4 , 7 , 38 , 40 , 45 ].
Doping of GaP with N leads to isoelectronic substitution of the host P atoms by N in its crystal lattice and to the creation of the electron trap with a giant capture cross-section. Note, that none of nanotechnology methods are used in the creation or selection of dimensions of these nanoparticles — only natural forces of electron—hole interaction and electron capture by the traps are necessary for the creation of these nanoparticles. As the result we get something like neutral short-lived atom analogue — a particle consisting of heavy negatively charged nucleus N atom with captured electron and a hole.
So-called zero vibrations do not destroy the possible solid phase of bound excitons having these heavy nuclei that give an opportunity to reach in GaP:N a new crystal state — the short-lived excitonic crystal appeared at the necessary level of excitation, N impurity ordering and concentration, energy of photons and temperature. Taking into account the above-mentioned preceding results, a model for the GaP:N long-term ordered crystal and its behavior at the relevant level of optical excitation for year-old ordered N-doped GaP Figure 14 can be suggested.
At the relevant concentrations of N, the anion sub-lattice can be represented as a row of anions where N substitutes for P atoms with the period equal to the Bohr diameter of the bound exciton in GaP approximately 10 nm Figure 14a. At some level of optical excitation, all the N sites will be filled by excitons, thereby creating an excitonic crystal Figure 14b , which is a new phenomenon in solid-state physics and a very interesting medium for application in optoelectronics and nonlinear optics [ 4 , 15 , 17 , 25 , 26 ].
The models of 40 years ordered GaP doped by N. The new type of crystal lattice with periodic substitution of N atoms for the host P atoms. The excitonic crystal on the base of this lattice. Thus, using bound excitons as short-lived analogues of atoms and sticking to some specific rules, including the necessity to build in the GaP:N single crystal the excitonic superlattice with the identity period equal to the bound exciton Bohr dimension, we get a unique opportunity to create a new solid state media — consisting from short-lived nanoparticles excitonic crystal, obviously, with very useful and interesting properties for the application in optoelectronics, nanoscience, and technology.
The following will discuss methods of preparation and possible application in optoelectronics of perfect GaP crystals, based on perfect GaP excitonic crystals and nanocrystals. Thus, confirmed by this semicentennial study, the impurities in doped long-term ordered GaP create a sublattice with a period that depends on their concentration.
The ordered crystals with the host lattice modified by impurities could be very useful in various optoelectronic applications. Noted here are only a few potential applications in light emissive device structures. The properties of these structures will be very stable and independent on time.
Uniform distribution of the recombination N and activator centers at the optimum concentration will yield the maximum efficiency for light emission. Further investigations of the quasi-crystalline state of excitons or bi-excitons bound to an impurity superlattice with a period equal to the Bohr dimension will be very interesting and useful because they should greatly strengthen nonlinear optical effects at low excitation intensities.
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This excitonic phase of high density of photons as an original accumulator of light also provides new opportunities for storage, transmission, and conversion of light. With significant recent progress in semiconductor thin film deposition and growth techniques in some specific cases of device optoelectronic structure preparation, there obviously will be no longer a need to wait during years for such ordering to occur. Further, the preparation of a two- or three-dimensional arrangement of N impurities in a GaP film is difficult but also possible with the help of ion lithography.
Of course, nowadays this technique is a frontier of our technological possibilities, but within the nearest future some very important progress likely will be obtained also in this direction. In this case, we will get a unique opportunity to design 3-dimensional impurity superlattices with configuration, symmetry, and lattice that are optimal for application in a concrete device structure or for efficient realization of specific linear or nonlinear optical phenomena.
In any case, independently on the method of creation, the impurity modified crystal lattices, the excitonic as well as bi-excitonic phase with translational symmetry are very interesting objects, the properties and possible application of which are now under our investigation. Nonlinear optics, starting its epoch-making development from the Nobel Prize Laureate N.
Bloembergen transaction [ 49 ], with the appearance of lasers and highly supported personally by one of their inventors, the Nobel Prize Laureate A. Prokhorov, who helped the author to found in the Laser Research Laboratory in the Academy of Sciences of Moldova, since s has taken its noteworthy place in investigations of GaP [ 5 , 7 , 50 - 52 ]. Here especially important for fundamentals and application in optoelectronic device structures were investigations of direct and indirect with participation of the lattice phonons many-quantum absorption between high symmetry points of GaP Brillouin zone Figure 1 , following the increase of photoconductivity and UV photon emission.
So, exciting these high symmetry points with the help of infrared photon of a Q-switched laser, we get photoconductivity with participation of different energy bands and UV photon emission that is important equally for the investigation of band structure and for application in light frequency convertors. Addition of new opportunities due to elaboration of defectless perfect GaP bulk single crystals, its top-quality nanoparticles and multi-layered structures, discovery of the new nonlinear optic medium — excitonic crystal and its very interesting nonlinear optical phenomena [ 25 - 27 ] will surge of interest to this crystal, giving a new prospective industrial method of perfect crystal preparation, as well as opportunities for efficient realization in optoelectronics and electronics in general of remarkable properties of semiconductors due to a big commercial advantage from their fabrication.
Since the time of original preparation of gallium phosphide doped by nitrogen crystals GaP:N by the author in the s, followed by the introduction of the excitonic crystal concept in the s, the best methods of bulk, film, and nanoparticle crystal growth were elaborated.
The results of semi-centennial evolution of GaP:N properties are compiled here and in the references to this paper. Novel and useful properties of GaP including an expected similarity in behavior between nanoparticles and perfect bulk crystals, as well as very bright and broadband luminescence at room temperature, are observed.
These results provide a new approach to the selection and preparation of perfect materials for optoelectronics [ 25 ] and a unique opportunity to realize a new form of solid-state host — the excitonic crystal [ 26 , 27 ]. In spite of the fact that the time necessary for natural long-term ordering years does not lead to optimism, the collected experience and results confirm expedience of the efforts directed to the formation in GaP of the N impurity superlattice having the identity period equal to the bound exciton dimension.
As noted in Ref. Except natural aging of the relevant crystals for years, preparation of the N superlattice for excitonic crystal can be also realized by known methods of growth of multi-layer films, in particular by molecular beam and laser-assisted epitaxy [ 46 - 48 ]. The excitonic crystal, created by the long-term ordering or by the noted above methods of growth of multi-layer films, as well as the bulk top quality GaP crystals with the unique optic properties, obtained by the long-term ordering process of freshly prepared crystals, will be used in the new generation of optoelectronic devices, sometimes instead of nanoparticles and a lot of other materials.
In particular, keeping in mind the low energy of the bound exciton creation, one can expect a low threshold for the generation of non-linear optical effects in the excitonic crystal and a good opportunity to create new and very efficient optoelectronic devices. Note that semiconductor nanoparticles were introduced into materials science and engineering mainly in order to avoid limitations inherent to freshly grown semiconductors with a lot of different defects.
However, it was shown [ 15 ] that this reason becomes unessential if, when justified, perfect long-term ordered semiconductor crystals are applied in electronics. Independently on their dimensions they demonstrate very interesting for application properties. Therefore, using the long-term ordered, perfect GaP crystals or similar on behavior and properties material in the electronic industry instead of the elaboration of very expensive and labor-consuming technologies for diverse materials and their nanoparticles with limited for application spectral region and other parameters, we get a big commercial advantage from their fabrication and application for details please see the paper [ 25 ].
All the obtained results presented here and included in summary reviews [ 15 , 17 , 25 - 27 ] may sufficiently change the approach to the selection of materials necessary for electronics, to make cheaper and simpler technology for the preparation of the selected materials and device structures based on them. This study of long-term convergence of bulk- and nanocrystal properties brings a novel perspective to improving the quality of semiconductor crystals. The unique collection of pure and doped crystals of semiconductors grown in the s provides an opportunity to observe the long-term evolution of properties of these key electronic materials.
During this half-centennial systematic investigation we have established the main trends of the evolution of their optoelectronic and mechanical properties. It was shown that these stimuli to improve the quality of the crystal lattice are the consequence of thermodynamic driving forces and prevail over tendencies that would favor disorder and destruction. Our long-term ordered and therefore close to ideal crystals repeat the behavior of the best nanoparticles with pronounced quantum confinement effect.
For the first time, to the best of our knowledge, we have observed a new type of the crystal lattice where the host atoms occupy their proper equilibrium positions in the crystal field, while the impurities, once periodically inserted into the lattice, divide it in the short chains of equal length, where the host atoms develop harmonic vibrations. In GaP it leads to the change in the value of the forbidden energy gap, to the appearance of a crystalline excitonic phase, and to the broad excitonic energy bands instead of the energy levels of bound excitons.
The high perfection of this new lattice sharply decreases non-radiative electron-hole recombination, increases efficiency and the spectral range of luminescence, and promotes the stimulated emission of light due to its amplification inside the well-arranged, defect-free crystal. The development of techniques for the growth of thin films and bulk crystals with ordered distribution of impurities and the proper localization of host atoms inside the lattice are our high priority. Semiconductor nanoparticles were introduced into materials science and engineering mainly to avoid limitations inherent to freshly grown semiconductors with a lot of different defects.
Here and in other publications we show that this reason becomes unessential if we will apply in electronics, when it is justified, perfect long-term ordered semiconductors, which demonstrate independently on their dimensions very interesting for application properties. Especially important for application in the new generation of light emissive devices are the predicted and investigated by us crystalline state of bound excitons in GaP:N, the discovered in the framework of the STCU Project [ 16 , 32 ] dramatic expansion of luminescence region in GaP perfect bulk single crystals as well as in the best prepared GaP nanocrystals and based on them composites with transparent polymers.
Using the long-term ordered GaP or similar on behavior and properties material in the electronic industry instead of elaboration of very expensive and labor-consuming technologies for diverse materials with their limited for application spectral region and other parameters, we get a big commercial advantage from their fabrication and application. So, the results of this long-term evolution of the important properties of our unique collection of semiconductor single crystals promise a novel approach to the development of a new generation of optoelectronic devices.
Besides the long-term ordering, the combined methods of laser-assisted and molecular beam epitaxies [ 46 - 48 ] will be applied to fabrication of device structures with artificial periodicity; together with classic methods of the perfect crystal growth, they can be employed to realize impurity ordering that would yield new types of nanostructures and enhanced optoelectronic device performance. For the first time we demonstrate that well-aged GaP bulk crystals as well as high quality GaP nanoparticles have no essential difference in their luminescence behavior, brightness, or spectral position of the emitted light.
The long-term ordered and therefore close to ideal crystals repeat the behavior of the best nanoparticles with pronounced quantum confinement effect. These perfect crystals are useful for application in top-quality optoelectronic devices and are a new object for the development of fundamentals of solid state physics. Of course, waiting for improvement of the crystal quality for tens of years can be justified only in exceptional cases, but we propose to turn this perennial procedure of long-term ordering into the necessary one for the preparation of the top quality material for industrial electronics, which due to its unique properties will be used in electronic devices instead of a lot of various materials.
I am glad to note that the broad discussion and dissemination of our joint results stimulate the development of our further collaboration with reliable partners from the USA, Russia, Italy, Romania, France, and other countries. I express my cordial gratitude to my teachers, the late world-known scientists: Professor Nina A. Prokhorov, Professors Rem V. Khokhlov, and Sergei I. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.
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Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract This chapter demonstrates the growth of perfect and contamination-free gallium phosphide GaP crystals and discusses the influence of crystallization conditions on their quality and properties. Keywords GaP long-term ordering excitonic crystal perfect semiconductors for optoelectronics. Introduction Single crystals of semiconductors grown under laboratory conditions naturally contain a varied assortment of defects such as displaced host and impurity atoms, vacancies, dislocations, and impurity clusters.
Growth Technology for Perfect GaP Bulk and Nano-Crystals Single crystals of gallium phosphide, in principle, can be obtained in several ways [ 1 , 3 , 7 ]. The method for obtaining gallium phosphide from solution-melt, chosen by us, has several significant advantages: A significant temperature reduction of the process and the presence of large amounts of solvent dramatically reduce crystal pollution by material of the container. The light sources creating on their basis have high efficiency. Optical Properties of Perfect, Long-term Ordered GaP:N Crystals It is necessary to note that the very important for optoelectronics long-term ordering and considerable improvement of the semiconductor crystal lattice and accompanying phenomena have been discovered and observed over decade time scales only with the help of the same unique collection of samples.
Tak D. Eugene M.
Topological phenomena in magnets and superconductors in the presence of quenched randomness due to impurities and lack of crystallinity. Leon Cohen. Kelle L. Low mass stars and brown dwarfs, optical and near-infrared spectroscopy, cool atmospheres, stellar content of the Solar Neighborhood.
Lev Deych. Theoretical analysis of solar cell systems, theoretical optomechaniscs, and physics of semiconductor nanostructures. Andrew F. The structure and representation theory of Lie groups, and Lie algebras; and their application to physics. Adrian Dumitru. Cherice M. Efrain Ferrer. Andrea Ferroglia. Theoretical high energy physics: I study the phenomenology of the strong and weak interactions in processes measured at high energy colliders by applying fixed order perturbatin theory and resummation methods.
Mark D. Kathleen E. Sriram Ganeshan.
Semiconductor Physics, Quantum Electronics & Optoelectronics
Dmitry A. Random-field and random-anisotropy magnets; relaxation and decoherence, including spin-lattice interaction, superradiance and phonon bottleneck magnetomechanical effects in nanomagnets; quantum transitions including Landau-Zener effect; spin tunneling in molecular magnets, including fronts of tunneling; magnetic deflagration; structure and dynamics of small magnetic particles, including internal spin waves; collapse of skyrmions in ferro- and antiferromagnets.
Swapan K. Contact Nick if you are interested. Learn More. Nature Photonics Cover October Welcome Sajal! Sept Sajal Dhara joins the group as a post-doc. Levi receives his PhD! Aug Congratulations Levi! He is the first person to a receive their PhD from Nick's group. Levi will continue as a post-doc.
One on optical trapping and the other on 2D materials. Near-field detection of optical plasmons published July Kenny's work on detecting optical plasmons with 2D materials is published. Congratulations Kenny! Kenny passes proposal exam July Congratulations Kenny on passing your thesis proposal exam! Welcome Robby! July Robby Petit joins the group to work on optical trapping.
Nature Nanotechnology June Welcome Necdet! June Necdet Basaran joins the group.
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THe had a second presentation with collaborators from RIT. Near-field measurement of graphene strain published Jan Congratulations Ryan on your paper published in Nanotechnology on the near-field measurement of strain in graphene. Check it out!