The paper presents unique functional capabilities of silicon with nanoclusters of impurity atoms with various characters. It is shown that, depending on the nature of the clusters, it is possible to expand the spectral diapason of sensitivity towards the IR region and obtain silicon with anomalously high negative mag-netoresistance (Δ ρ/ρ > 100%) at room temperature. The formation of clusters of impurity atoms with different nature and concentration in the lattice of semiconductor materials is a new approach for obtaining bulk-nanostructured silicon with unique physical properties.
Practically all of the main functionalities of existing semiconductor materials have been entirely well studied and used in the sphere electronics [
The forward electronics development requires semiconductor materials with the new basic properties, fundamental parameters and physical phenomena in them. At the same time, the development of semiconductor materials science should focus on ensuring the development of new electronics industries: new directions in functional and integral electronics, the use of nanophotonic materials in nanoelectronic devices, and also photovoltaic energetics and optoelectronics.
Each of these fields required individual class of materials with certain physical properties and fundamental parameters. So, for instance, to provide cheap and highly efficient fiber-optic communication based on passive optical network technology, it would necessary to create low cost prices of LED emitters in the range of λ = 1.5 - 1.6 micron, as well as photodetectors with highly sensitive high-speed for working in this spectral region. However, at present, there are practically no existing low cost semiconductor materials and respectively technologies make it possible to massively create such devices [
The development of some nanoelectronic directions is determined due to need of developing technology for bulk nanostructured semiconductors with controlled parameters of the structure, composition, and other properties of nanoobjects. Obtaining such materials will allow a creation of new types of materials photon, as well as materials unique functionality of nanoscaled superlattices. However, the modern technology of nanostructure formation also does not allow obtaining such materials on a wide scale [
As is known, a low of efficiency of modern industrial silicon photovoltaic cells (up to 20%) is associated with inefficient use irradiation of solar energy in the region of the spectrum with the range λ = 1.2 - 3 micron (about 40% of the total solar irradiation), and also with the effect thermalization of photogenerated charge carriers associated with the absorption quants of light with the energy hν > Eg. Some calculations [
The high efficiency of multicascade photovoltaic cells which based on semiconductor compounds of АIIIВV [
There is some question arises: can we create semiconductor materials, in terms of their physical properties and fundamental parameters, to ensure the development of modern electronics and photovoltaic energetics?
Studies carried out in the last 15 - 20 years have shown the technology of “low-temperature” diffusion doping developed [
Depending on the nature of impurity atoms, it is also possible to form magnetic and multicharged atomic clusters [
The sample was a p-type single-crystalline silicon with a resistivity of ρ = 3 - 5 Ω * cm, with an oxygen concentration N = 4 × 1017 cm−3, a dislocation density of S ~ 10 cm2, and a surface orientation. Samples with nanoclusters of nickel and manganese atoms were prepared according to the technology developed [
In
From the surface of the samples obtained, 50 micron silicon was removed step by step to the middle of the sample thickness and the state of the clusters was studied using an IR microscope.
As the results showed, no significant changes were observed. This means that the clusters are distributed uniformly throughout the bulk of the crystal. At the same time, in the samples subjected to additional thermal annealing at T = 850˚C an interesting phenomenon is observed, that is, the clusters are enlarged and their ordering begins (
As is known in silicon [
The spectral dependence of the photoconductivity of the samples under study is shown in
observed in them. Firstly, the photoresponse begins at hλ = 0.12 - 0.13 eV (λ ~ 10 micron, at T = 100 K), which can not be explained from the standpoint of electron statistics. In addition, as known, manganese atoms in silicon create two donor levels with an ionization energy E1 = EC - 0.27 eV, E2 = EC - 0.5 eV [
The “low-temperature” diffusion technique developed [
Moreover, a very interesting and new phenomenon was discovered―the possibility of controlling the value of NMR over a wide range of values, including even the possibility of changing the sign of the MR (the transition from NMR to positive MR) under the influence of illumination in the region of intrinsic absorption. As was shown in
These results indicate that a photomagnetic phenomenon is observed in the materials under study, which is absent in ordinary magnetic semiconductors. Therefore, we can say that these amazing phenomena in silicon with magnetic clusters will lay the foundation for a new scientific direction in the field of semiconductor materials science with the possibility of using them for developing fundamentally new photomagnetic devices.
The developed technology of successive doping of silicon with impurity atoms of sixth group (sulfur, selenium) and iron group with subsequent heat annealing under certain thermodynamic conditions made it possible to form binary clusters in the silicon lattice, creating nuclei of a new phase in the bulk-new elementary cells in silicon. At the same time, silicon, sulfur and manganese atoms are located at the adjacent lattice sites and formed electrically neutral molecules as a type S++Mn−−. As a result, a new elementary lattice cell of the type Si2S++Mn−− is formed (
All this stimulates their self-organization and self-restructuring. The results of the research show, with an increase in the concentration of impurities, the association of elementary cells of the Si2S++Mn−− type occurs, with the formation of more complex structures that form nucleus of a new phase (nanocrystals) of sulphides, selenides or tellurides (SMn compounds) in the silicon lattice (
This is due to the fact that unlike silicon, new phases can have a direct-band structure, which increases the probability of interband optical transitions by several orders of magnitude.
Therefore, it can be argued that silicon materials with binary nanoclusters can be used as promising materials for photovoltaic energetics, allowing them to create more efficient photovoltaic cells [
There is main parameters (Isc and Vov) were investigated in a special setup, which practically completely excluded light from the incident solar radiation with a quantum energy corresponding to intrinsic absorption in silicon. Lighting of the photovoltaic cells was carried out through a 5 mm thick silicon filter made of high-resistance silicon providing absorption of radiation with hν > Eg, but transmitting more than 30% of the long-wavelength infrared solar radiation. As a control, a solar cell was used for industrial production.
As can be seen from
As can be seen from the figure, an appreciable short-circuit current appears even at hν > 0.4 eV (λ = 3 micron). All these data allow us to state that when developing optimal alloying conditions using specially selected impurity atoms, it is possible to expand the spectral region of silicon sensitivity substantially and, on this basis, to develop more efficient solar cells.
The sensitivity of photovoltaic cells made on the basis of silicon with binary
In the presence of filter | Industrial photovoltaic cell | Photovoltaic cells based on binary cluster | |||
---|---|---|---|---|---|
I | II | III | IV | ||
203 | 170 | 150 | 90 | 35 | |
NS и NMn | ? | 1016 | 3 × 1016 | 5 × 1016 | 1017 |
clusters in the long-wave part of the IR spectral region (λ = 3 micron) will allow them to be used as IR photodetectors necessary for creating pyrometric temperature with the range 500 - 900 K.
All of the results obtained give reason to believe that silicon with nanoclusters of various nature is indeed a unique material in the field of semiconductor materials science. Therefore, the main task is the further development of technologies for obtaining such materials with controlled properties and composition of clusters, as well as the study of their electrical, photoelectric optical and magnetic properties, which will allow us to correctly estimate their functional capabilities for photoenergetics and electronics.
This work was financially supported by Science and Technology projects Project Proposal for Uzbek-China Research Program “National Key R&D Program of China”, №2016YFE0120900.
Bakhadyrhanov, M.K., Sodikov, U.X., Melibayev, D., Wumaier, T., Koveshnikovm, S.V., Khodjanepesov, K.A. and Zhan, J.X. (2018) Silicon with Clusters of Impurity Atoms as a Novel Material for Optoelectronics and Photovoltaic Energetics. Journal of Materials Science and Chemical Engineering, 6, 180-190. https://doi.org/10.4236/msce.2018.64017