Heterogeneous Compositions based on Si, Ge and C
Investigation of the Growth Processes Originating from Gas Phase in Vacuum and Production of Test Heterogeneous Compositions based on IV Group Elements (Si, Ge, C) and their Solid Solutions
Tech Area / Field
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
- PHY-SSP/Solid State Physics/Physics
3 Approved without Funding
VNIIEF, Russia, N. Novgorod reg., Sarov
- Institute of Physics of Microstructures, Russia, N. Novgorod reg., N. Novgorod\nNizhni Novgorod State University name after N.I. Lobachevsky, Russia, N. Novgorod reg., N. Novgorod
- MEMC Electronic Materials S.p.A., Italy, Novara\nManchester Metropolitan University, UK, Manchester
Project summaryThe objective of the project is to study the growth processes originating from gas phase in vacuum and production of heterogeneous compositions based on IV group elements (Si, Ge, C) and their solid solutions.
The last decade was marked by the noticeable advance of Si based active elements in millimeter wavelength range. The success was basically due to heterostructures based on Si, Ge and their alloys involved. Active application of nano-dimensional heterocompositions in general cells of micro- and optoelectronics stimulated some interest to the persification of the materials used in electronics. Of special interest is implementation of carbon, significantly expanding the capabilities of the traditional Si-SiGe heterocouple at construction of silicon heterostructures.
Implementation of carbon in silicon technology as a constituent element of solid solutions is however associated with significant obstacles, stipulated, in particular, by carbide formation problem, which can not be solved without a detailed analysis of film crystallization process and study of the phenomena occurring at the surface of the growing layer.
One of the ways to solve the carbide formation problem in silicon is to find the corresponding, mainly low-temperature conditions of growth of homogenous layers of triple solid solutions Si1-x-yGexCy. Another way is to form multilayered heterostructures including Ge and Ge1-xCx intermediate layers between Si and C ones, which prevent mixture due to diffusion processes and segregation of carbide-forming components at the vicinity of heteroboundaries.
Following the above, the most attractive issue is the problem of heteroepitaxy on different substrates of quantum multilayered nano and heterostructures based on binary
Si1-yCy, Ge1-yCy and ternary Si1-x-yGexCy solid alloys, to be further used as the elements of solid-state high-frequency (including terahertz range) electronics. The most attractive applications of heterocompositions being considered herein are associated with development of non-stressed heterostructures with deeper if compared to Si/SiGe thermocouple electronic transport channels (MODFET structure) and formation of the effective cascade structures, including those with resonance-tunneling barriers based on solid solution of Si1-yCy which further might be replaced by diamond or silicon carbide barriers as the technology will be mastered. These structures could be useful for increasing the efficiency of traditional silicon devices with the transit-time effects (avalanche-transit and tunnel-transit diodes) in the millimeter wavelength range. Periodical heterosystems based on germanium are still attractive from the viewpoint of development of hot medium lasers based on them (thin-film option for such lasers has been yet implemented by no one) and long-range IR wavelength photo-receivers. The last based on transition from both mixed leves and magnetic quantification levels are being actively discussed at present.
In accordance with the above the prioritized activities pursued within the present project are:
- Search for the optimal technological conditions for growing Si1-x-yGexCy solid solutions on silicon and germanium substrates using vacuum has-phase epitaxy tecnology in the entire range of the compositions and layered periodical haterocompositions based on Si, Ge, Si1-xGex, Si1-xCx and Ge1-yCy layers. The main focus will be on study of
Ge1-yCy layers and periodical Si1-xGex/Ge1-yCy heterocopositions, including non-stressed Si(Ge)/Ge1-yCy heterostructures on silicon substrates. At the same time the diagnostic methods implied for nanocentimeter layers should be improved to control layer compositions, their thickness, the value of elastic deformation accumulated in the layers, the character of interfaces, as well as to solve the problem of specification the height of the barriers of Si1-xGex/Ge1-yCy heterojunction formed in the wide range of solid solution compositions.
- Growing both one-layered and two-layered Si(Ge)/Ge1-yCy, Si(Ge)/Si1-yCy and Si(Ge)/Si1-xGex heterocompositions to master the technological conditions for growing the structures in all the range of compositions and to define the principal capabilities of the technological equipment involved for growing far more complicated heterocompositions.
- Growing and study of the periodic heterostructures based on germanium, including SP(Ge1-yCy–Ge1-xSix)/Ge (111) and CP_Si-Ge1-yCy)/Si (100) substrates. Similar SP(Ge–Ge1-xSix)/Ge(111) and CP)Si-Ge)/Ge (111) structures were grown by the authors earlier using gas-phase hydride technology at the atmospheric pressure, which offered certain problems due to the high growth rates and hardly implementable low growth temperatures when Si substrates were involved. A lot of varying effects related to two-dimensional holes has been found and investigated with these samples. The presently developed high-vacuum equipment involving the hydride and hydrocarbon sources allow us to overcome the problems mentioned above.
- Growing and study of transistor heterostructures based on Si and SiGeC solid solutions grown on the silicon substrates. This endeavor (related to development of high-frequency modulation-doped field-effect transistor MODFET) is a prioritized one for many laboratories world-wide due to the significance of the problem. We intend to succeed in producing such heterostructures focusing especially on the use of Ge1-xCx layers with high carbon content.
- Investigation of crystalline lattice structure, deformation characteristics as well as the structure of extended defects formed using X-ray structural analysis, metal graphic and electronic graphic methods, scanning and transmission electron microscopy; investigation of the energy-band structure parameters of the Ge1-yCy and Si1-x-yGexCy layers as well as the electron states at Si(Ge)/Ge1-yCy and Si(Ge)/Si1-yCy interfaces by optical and electrical methods; theoretical analysis of the observed dependencies to determine parameters of the electron-hole gas in the layers and characteristics of barriers generated at heterointerfaces.
The activities under the project will result in further understanding of the basic growth regularities and development the technology providing growth in vacuum from gas phase of the brand new complex multilayered heterostructures based on the entire range of IV group elements for some applications in micro- and nanoelectronics.
Previously the problems of heteroepitaxy were studied by the project team in NNGU, disposing of gas phase and molecular-beam epitaxy facilities. However, the main attention in our previous activities was focused on growing Si-Ge heterostructures and the problem of doping the same. As a consequence, the process of carbide formation was considered as a parasite effect, preventing the growth of perfect monoclrystal layers. As it follows, the capabilities for implementation of carbide-containing compositions were not foreseen for the equipment involved.
However, the methods for substrate surface treatment preceding epitaxy were mastered quite thoroughly, including such non-traditional materials as germanium, sapphire, fionite and others. Significant attention was also paid to investigation of every possible phenomena occurring in nanostructured materials, and to theoretical developments related to interaction of molecular and atomic substance flows with the surface.
In the last few years during ISTC Project #2372 fulfillment the technological facility implementing purely gaseous sources, equipped with the sufficient number of gas lines employing hydrides and hydrocarbons as the operational substances was commissioned in IMP RAS (Nizhniy Novgorod) with the active participation of RFNC-VNIIEF. The facility provides film growth under the operating gas pressures from 10-6 Torr to 10 mTorr. To produce the extremely low vacuum, the installation is equipped with the diffusion pump featuring high pumping speed and some preparatory activities for installation of a turbo-molecular pump are being done (the capability to install the additional sublimation and magnetic discharge pumps is available). Pyrolysis of the input substances is done either at the heated substrate (T = 400 – 1200oC) or at the additional element heated up to 1500oC. As a follow-up step we foresee to install some additional elements for production of low-temperature plasma, contributing to accelerated pyrolysis on the substrate (like UV lamps, ions accelerating the of electric potential between the substrate heater and the additional furnace, resonance UHV sources). The decreased pyrolysis temperature can be achieved by adding the high-molecular elements featuring the lower activation energy of molecule decay.
To modify the crystalline properties of heterostructures, the latter can be irradiated with the average energy ions generated by the implanting setup located in NNGU with further burnout of the plates, including the local one, by powerful optical VNIIEF-developed laser radiation.
The project team is adequately experienced in forming both multilayered heterostructures, including the quantum ones, based on silicon and germanium and in studying their characteristics by different methods, including the methods of structural investigations: transmission and scanning electronic microscopy, X-ray and diffraction analysis, Auger and mass spectrometry, and the methods to analyze their electronic characteristics: optical, electro-physical, paramagnetic resonance etc. The well-established cooperation with another groups, including the foreign ones, involved into the similar activities is pursued. The team also has some experience in growing the diamond microcrystalline films on nickel as well as diamond microcrystals and silicon carbide films on silicon. In particular, we have demonstrated the leading role of the effect of silicon sublimation at high-temperature (~1000oC) growth of SiC (111) films on Si (111) with only carbon hydride component involved. The differences characteristic to formation of the carbide phase when the above mentioned method of SiC films growth at silicon surface and growing of the same from the mixture of silane and hexane at lower epitaxy temperatures (700C) is implemented were revealed. Some members of the team were long involved into a study of crystal lattice modification of Si films by ion beams, including the structural transformations in films yielding super-thin diamond layers as a result of the effect induced by hypersonic pressure pulses, excited at irradiation of plates (on the reverse side) by nitrogen average energy ions. The activities devoted to technological supplies and the metric of the structures being grown were accompanied by the theoretical work on the kinetics of growth processes accomplished at molecular-beam epitaxy facility based on gas sources.
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