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PROJECTSof the MOVPE Laboratory, Department of Semiconductors, Institute of
Physics
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This project aims at the development of semiconductor Quantum Dots (QDs) based on InAs/GaAs and later from GaSb, using MOVPE. Optical and electrical properties of QD structures are often determined more by the size and shape, than by the material of the QDs, because of the comparable size of QDs and de Broglie´s wavelength for electrons and holes. The type of the structure, (number of QD layers and their separation in the vertically correlated structures) will play important role in the optimisation of QD structure parameters. The above mentioned properties are determined by the technology of preparation. The QD parameters will be adjusted by changing the growth rate, precursor ratio, time regime of the growth and by other technological parameters like the substrate orientation. The dominant application of QD is in the field of light sources. In the frame of this project we want to investigate QD structures also for use in the detectors and eventually memories.
Knowledge of accurate data on vapour pressure of metal organic precursors such as carboniles, acetylacetonates or metalocenes is essential for control and modelling of growth of semiconductor and metallic layers, nanostructures and nanoparticles. These structures are indispensable in optoelectronics and high speed electronics, in preparation of new semiconductor, dielectric, magnetic and ceramic materials, in catalysis and related chemical processes. Data on vapour pressure of metal organic precursors presented in literature often exhibit a great scatter or are unknown. Static apparatuses for vapour pressure measurement developed at ICT Prague and at IP AS CR (the latter for toxic and dangerous materials) are suitable for highly reactive precursors having low vapour pressure. The project is aimed at measuring and critically assessing vapour pressure data of metal organic and related precursors containing Ni, Fe, Mn, In, Sb and Li used in MOVPE and CVD.
This project aims at the development of semiconductor Quantum Dots (QDs) with predetermined and controlled size and shape from InAs and later from GaSb, using MOVPE. Optical and electrical properties of QD structures are often determined more by the size and shape, than by the material of the QDs, because of the comparable size of QDs and de Broglie´s wavelength for electrons and holes. The type of the structure, (number of QD layers and their separation in the vertically correlated structures) will play important role in the optimisation of QD structure parameters. The above mentioned properties are determined by the technology of preparation. The QD parameters will be adjusted by changing the growth rate, precursor ratio, time regime of the growth and by other technological parameters like the substrate orientation. The dominant technology for QD preparation structures is MBE. In the frame of this project we would like to prove that MOVPE is equally suitable method for this task.
New mid-infrared sources for photonic sensors (NEMIS)
The NEMIS
project aims at the development and realisation of compact and packaged vertical-cavity
surface-emitting semiconductor laser diodes (VCSEL) for the 2-3.5µm wavelength range and
to demonstrate a pilot photonic sensing system for trace gas analysis using these new
sources. The availability of electrically pumped VCSELs with their low-cost potential in
this wavelength range that operate continuously at or at least near roomtemperature and
emit in a single transverse and longitudinal mode (i. e. single-frequency lasers) is
considered a basic breakthrough for laser-based optical sensing applications. These
devices are also mode-hop-free tuneable over a couple of nanometers via the laser current
or the heatsink temperature. They are therefore ideal and unmatched sources for the
spectroscopic analysis of gases and the detection of many environmentally important and/or
toxic trace-gases, which is a market in the order of 10 million Euro today with an
expected increase into several 100 million Euro with the availability of the new VCSELs.
The aim of the project is to optimize the morphology of QD for application in active layer of QD lasers. The proper luminescence energy (wavelength of 1.3 micrometers and 1.55 micrometers), sufficient distance of the ground and excited transitions, and good homogeneity have a great importance for the optoelectronic applications of quantum dots (QD). All these properties can be controlled by the technology of the capping layer above the QD. We will examine an impact of the growth rate of the capping layer, its composition (InGaAs, AlGaAs), and partial pressure of the arsin on the properties of produced dots. Prepared structures will be investigated by PL, MPL, TEM, and AFM. Using the proper model of quantum dots (based on the approximative separation of the coordinates and including the effects of the strain), the dots shape and size, homogeneity of the dots ensembles, and effective masses of the electrons and holes will be determined.
Project of the Group of Optical Measurements and Transport Theory, our Deapartment of Semiconductors, Inst. of Physics, AS CR Preparation of high brightness luminescent vertically stacked multiple-layer InAs quantum dots (QD) structures with defined properties; the emission wavelength, the energy difference between the QD first excited and ground states and the density of QDs. Stacked multi-layer QD structures will be prepared by Metal Organic Vapour Phase Epitaxy, using Stransky-Krastanov growth mechanism. Parameters like the number of stacked layers, the thickness of GaAs spacer layers, thickness and chemical composition of strained buffer layer will be used to control properties of vertically stacked multiple-layer InAs QDs structures. Optimised structure will be incorporated into GaAlAs/GaAs waveguide. Samples will be characterized by structural methods (X-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy (AFM)) and optical methods (luminescence, magneto-luminescence, absorption, photomodulated reflectance, elipsometry and photoconductivity). Electronic structure of QDs will be calculated and the results of calculation will be used to modelling of optical properties of prepared structures. The aim of these studies is to contribute to control preparation of stacked multiple-layer structures of quantum dots and to understand their properties in dependence on the value main parameters of these structures.
The InAs quantum dots (QDs) in GaAs embedded in AlGaAs barriers will be studied by ballistic electron emission microscope BEEM). The detailed space resolved ballistic electron emission spectroscopy (BEES) on these QDs will be the main aim of the project. The density of states and the transmissivity of individual quantum states will be mapped in QD. The special software will be developed for realization of such measurements. The samples will be prepared by MOVPE (Metal Organic Vapor Phase Epitaxy) technique and results of measurements will be compared with results measured on MBE (Molecular Beem Epitaxy) grown samples (University of Nottingham). The results contribute to increasing knowledge about QDs which are necessary for development of high efficient lasers, ultrasmall memories and single photon sources.
New materials, such as quantum-dot materials and self-organised semiconductors, are of key importance in a variety of components with high performance. The demanding technologies needed for research on those materials are the focus of this theme. As in the network theme Towards technologies for photonic large scale integration and Nanophotonics for advanced integration schemes the complexity and cost of those technologies are the key motivation for integration of research.
The precise knowledge of precise vapour pressure data of metal organic precursors is indispensable for MOVPE process optimisation - now the main epitaxial technology for optoelectronic and ultrafast electronic components. The wide scatter of the published data has not been systematically and critically assessed yet, to give the user up to date and reliable data. Because of the pyrophoric nature of metal organic precursors the most suitable measuring technique for vapour pressure is the static method. The third generation of the vapour pressure static apparatus designed at ICT Prague has a minimised electro polished internal surface, ultrahigh vacuum design with two turbomolecular pumps, precise temperature control and uses a differential pressure gauge MKS Baratron. We have recently published the true vapour pressure data of high purity DEZ, TESb, TEAl, TEGa. The measurement was carried out in the temperature range used for MOVPE. The objective of the project is to measure, critically assess and eventually update the vapour pressure data for other old and new metal organic precursors used for MOVPE.
To explain the discrepancy between the experimental results and
theoretical models of the shift of emission energies of luminescence and absorption edge
of laser structures with changing configuration of ultrathin InAs layers in the active
region.
Preparation of single- and multiple-layer structures of quantum dots (QD) with emission wavelength above 1.3 microns. QDs will be prepared by MOVPE, using Stransky-Krastanov growth mechanism. QD structures will be grown using InGaAs system. The emission wavelength will be adjusted by changing the composition of QDs and barriers, which controls the lattice constants and gap. Samples will be characterised by X-ray diffraction, optical methods and microscope techniques. The aim of these studies is to contribute to understanding of the electronic structure in QDs in dependence on the composition of QDs and barriers.
Structures with high values of misfit (5-7%) and strain may result in two possible epitaxial structures according to technological parameters: quantum dots (QD) and isovalent delta-layers (IDL) - i.e. ultrathin quantum wells with thickness of only few atomic layers. The use of these structures in laser active region may lead to much better parameters compared with conventional quantum wells lasers (lower threshold current density, better temperature stability of threshold current, higher differential efficiency, higher power and lower losses). The main part of the work will be devoted to the design and MOVPE preparation of QD and IDL structures based on InAs/GaAs and InSb/GaSb, optimisation of technological parameters of preparation and increasing localization energy in QDs. Structures suitable for laser active regions in desired wavelength ranges (1300nm - the window in fibre waveguides, midinfrared region) and AlGaAs waveguide prepared without destroying the QD luminescence be the main goal. The aim will be to solve quantitatively some questions, which are at present subjects of intense discussion as energy spectra of the conducting and valence band in IDL or mutual influence of IDLs causing red shift of photoluminescence peaks. It is impossible to explain this red shift only by overlapping of electron wavefunctions. Polarization measurements should evidence the dimensionality of our structures and bring some information about the strain inside QDs.
The objective of the project is to develop a microsystem for infra red spectroscopy, that will be integrated in a cost effective optical device for the measurement of natural gas calorific power. This device targets the gas distribution network, where the quantities are large. The measurement will be based on gas composition analysis by infrared spectroscopy. The laser technology has been retained to achieve this component. Three different types of lasers will be studied within the project. The objectives of the project are to select one laser solution and to achieve the integration of the retained solution.Three European end users will test and validate the whole optical device. MOVPE prepared materials and structures for
electronics and optoelectronic devices Czech participating organisations: Charles University, Prague, Faculty of Mathematics and Physics, KMF Development of the Metal-Organic Vapour Phase Epitaxy technology (MOVPE) of thin & ultrathin layer for deposition of III-V semiconductors. Co-operating laboratories both inside/outside the Institute have mastered a wide range of characterisation techniques and have started their own programmes based on MOVPE generated structures. Concentrate our efforts: Quantum Dots, Wells. Optical waveguides, Ohmic contact. Active waveguide structures, Opitcal sensor structures, Diodes and transistors based on quantum effects. Defects in multiple QDs, strained superlattices (SL). Focus our expected publication efforts on fundamental aspects of quantum dimensional objects (QW, QD) and on behaviour of different types of AIII-BV heterointerfaces.
MOVPE prepared materials and structures for electronic and
optoelectronic devices in cooperation with: Department of
Semiconductor Physics Faculty of Mathem. and Physics, Charles University, Prague, CR During the period of the last six years Institute of Physics AV-CR has gradually developed the MOVPE (Metal-Organic Vapour Phase Epitaxy) technology of thin and ultrathin layer deposition of III-V semiconductors. Co-operating laboratories both inside as well as outside the Institute have mastered a wide range of characterisation techniques and have started their own programmes based on MOVPE generated structures. In the coming three year period of continuing co-operation of Academic and University research groups (MFF-Charles Univ., UIPL-Chem. Univ., FEL-Czech Tech. Univ., PrF-Masaryk Univ.) we would like to extend the use of our technological and characterisation expertise for the preparation of device type semiconductor structures or structures otherwise related to solving application problems. We would like to concentrate our efforts in the following fields: Quantum Dots - (QD), Quantum Wells - (QW) including strained structures for semiconductor lasers or detectors, Hall sensors - (FzU). Photovoltaic structures with QWs (MFF). Optical waveguides and ohmic contacts (VŠCHT). Active waveguide structures, Sensor structures, Resonance tunnelling (FEL). Multiple QD structures and misoriented superlattices studied by X-ray techniques, (PrF-MU). Besides we would like to focus our publication efforts on the study of quantum dimensional objects (QD, QW, SL) and practical aspects of the behaviour of different types of heterointerfaces. Quantum dots in AIIIBV
semiconductors in cooperation with: Department of Solid State Physics, Faculty of Science, Masaryk University, Brno, CR
Surface migration and reconstruction in the
kinetic of AIIIBV layer growth and a new model for the
calculation of the point defects concentration in cooperation with: Institute of Radio Engineering and Electronics, Academy of Sciences, CR The basic theory of the Burton-Cabrera-Frank (BCF) has been developed to describe the growth mechanisms when single atoms or molecules are adsorbed from its vapour, than migrate to the surface steps and along steps to the kinks. In the case of deposition AIIIBV compounds by Mo VPE or MBE and their modifications the situation is more complex. A rough estimate of Xs ( mean displacement before reevaporation) gives different values for different substances composing the layer and composition of adsorbed molecules, which is different for different growth condition. The aim of the project is the theoretical description of the more complex surface migration and reconstruction processes. Finally, the point defect concentration in MO VPE grown layers we will try to calculate since the LPE formalism is not sufficiently accurate at MO VPE growth condition. Preparation of AIIIBV type
II Semiconductor Heterointerfaces and their Characterisation
in cooperation with: Ioffe Physicotechnical Institute St. Petersburg, Russia The idea of the project is to make use of selected physical characterisation techniques (low temperature luminescence, X-ray diffraction, Raman spectroscopy, X-ray microanalysis, scanning electron and atomic force microscopy and transport measurements) for the study and optimisation of the heterointerfaces in epitaxial layers, heterostructures, multiple quantum wells and superlattices of AIIIBV semiconductors, namely binary, ternary and quaternary compounds (in the GaSb/InAs/GaAs/AlAs systems). These structures will be prepared using the one and only LP-MOVPE machine in the Czech Republic (AIXTRON 200). The main interest will be focused on the recombination processes at heteroboundaries of type I. and type II., using photo and electroluminescence measurements and their theoretical analysis. New physical concepts for optimisation of coherent light sources for the mid infrared region (2-5microns) should be the practical results. This project will make use of the equipment and expertise gained during the work on preceding EC and GA CR projects in last four years. Hodnocení GA AV: (1998 - 2001) "Preparation and characterisation of GaSb based MOVPE epitaxial layers and structures" The aim of the project is to characterise and optimise the growth of GaSb based semiconductor layers from different precursors using Metal-Organic Vapour Phase Epitaxy (MOVPE). These materials may be suitable mainly for the preparation of detectors and laser diodes emitting in the mid-infrared range. As precursors, the following materials will be used: trimethylgallium (TMGa) or triethylgallium (TEGa), arsin (AsH3) or tertiarybutylarsin (TBAs), trimethylaluminium (TMAl) or tristertiarybutylaluminium (TTBAl) and trisdimethylaminoantimony (TDMASb) or triethylantimony (TESb), while the suitability of using the given precursors will be discussed and compared from the viewpoint of mutual compatibility during growth as well as from the viewpoint of their thermal decomposition and thus also the quality of the layer prepared. We can expect that the layers, prepared from newly developed precursors which thanks to weaker chemical bonds of metal-organic radical show lower decomposition temperature, could be of better quality than the currently prepared layers. Sample growth will be performed under various technological conditions, while specification will be gradually performed of separate layers prepared from different precursors using helium temperature photoluminescence, Hall effect, different microscopic techniques, X-ray diffraction and Raman spectroscopy.
Advanced Room Temperature Mid-infrared
Antimony-based Lasers by MOVPE in cooperation with: EPICHEM, Bramborough, UK Detectors operating in the mid-infrared require efficient light sources, those based on antimonides will be investigated. The consortium will develop the optimum precursor system to allow MOVPE growth of laser structures. Low temperature precursors are required due to the low melting point of InSb employed in the structure. The main basic research problem is connected with the increasing role of nonradiative recombination processes with increasing operating temperature. Since the goal of the project is to approach the limits of room temperature operation, the recombination processes have to be understood in great detail. Investigation of device design and comparison with MBE material will also be performed. Monitoring for CH4 and CO2 in the atmosphere and in combustion engine exhaust are the main areas for final device use.
Support for Advanced
Room Temperature Mid-infrared Antimony-based Lasers by MOVPE Research structures for Microelectronics prepared
by Metalorganic Vapour Phase Epitaxy
Souhrn výsledků: Hodnocení GA ČR:
Control of Enviromental Pollution by Tunable
Diode Laser Absorption Spectroscopy in the Spectral Range 2 - 4 µm in cooperation with: UM2 University of Montpellier,
France
METOVAPCO (1995 - 1996) in cooperation with: DAS Dresden, Germany |
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e-mail address: mailto:movpe@fzu.cz
Project of the 
European Community 
