ZnO layers deposited by Atomic Layer Deposition

The structure of 40 nm thick epitaxial ZnO layers grown on single crystalline sapphire and GaN substrates by atomic layer deposition has been studied using transmission electron microscopy. The growth is carried out between 150°C and 300°C without any buffer layer using di-ethyl zinc and water precursors. The ZnO layer on sapphire is found to be polycrystalline, which is probably due to the large misfit (~15 %) and the relatively low deposition temperature. However, the small misfit (~1.8 %) between the ZnO layer that is deposited on GaN at 300°C resulted in a high quality single crystalline layer

THERMAL DECOMPOSITION OF COMPOUND SEMICONDUCTORS COVERED WITH THIN METALLIC LAYERS

The aim of these investigations was to study the processes taking place during the heat treatment of compound semiconductor structures covered with thin metallic layers. This situation models the heat treatment of metallized wafer in the device technology. To investigate these samples a liquid nitrogen cooled UHV system was constructed, and the volatile component loss during the heat treatment was measured with a quadrupole mass spectrometer. The output signals are collected and evaluated by microcomputers. Special care was taken for the precise measurement of the sample to ensure the exact determination of the large peaks in volatile component loss. This method is suitable not only to measure the evaporation of the volatile component during annealing as a function of temperature, but to provide samples annealed in well- controlled circumstances for later investigations. As an example the measurement of the resistance of selected alloyed samples will also be shown

Determination of the thickness distribution of a graphene layer grown on a 2" SiC wafer by means of Auger electron spectroscopy depth profiling

Auger electron spectroscopy (AES) depth profiling was applied for determination of the thickness of a macroscopic size graphene sheet grown on 2 inch 6H-SiC (0001) by sublimation epitaxy. The measured depth profile deviated from the expected exponential form showing the presence of an additional, buffer layer. The measured depth profile was compared to the simulated one which allowed the derivation of the thicknesses of the graphene and buffer layers and the Si concentration of buffer layer. It has been shown that the C made buffer layer contains about 30% unsaturated Si. The depth profiling was carried out in several points (diameter 50m), which permitted the constructing of a thickness distribution characterizing the uniformity of the graphene sheet

Kvantitatív elektronmikroszkópia = Quantitative transmission electron microscopy

A projekt keretében kvantitatív transzmissziós elektronmikroszkópos módszereket fejlesztettünk, majd e módszerek használhatóságát anyagtudományi problémák megoldása során demonstráltuk. "Imaging plate (IP)" segítségével végzett nagy pontosságú (egy millió szürkeségi fokozatot megkülönböztető) méréseinket használtuk mind a valós térbeli (HRTEM) képi információ, mind pedig a reciprok térbeli diffrakciós információ kisérleti rögzítésére. Új módszert dolgoztunk ki az elektron diffrakciós (ED) ábrák, valamint HRTEM képek kvantitatív feldolgozására nanokristályos vékonyrétegek kvalitatív és kvantitatív fázisanalízise, valamint egyes kristály szemcsék indexelése céljából. A méréseket szerkezeti modellekből számolt mennyiségekkel (HRTEM szimuláció, kinematikus diffrakció) hasonlítottuk össze. Inhomogén, összetett szerkezeti modellek megalkotását (atomi koordináták számítását) is saját fejlesztésű programunk segíti. Módszereinket a következő problémák megoldásánál használtuk: grafén sík-darabokat tartalmazó CNx-szerkezetek kialakulása; félvezetők (Ge, Si) és fémek reakcióinak kezdeti szakaszai; légköri eredetű koromszemcsék és vulkanikus szilikátok felépítése; beágyazottan izolált Co-szemcsék előállítása és fázisszelekciója; SiC poláros tulajdonságainak hatása a növekedésre; Cu/Mg multirétegekben az intermetallikus nukleációjának aszimmetriája. Eredményeinket nemzetközi konferenciákon és iskolákon mutattuk be és 11 referált folyóiratcikkben közöltük (kumulatív impakt faktor 27,24). | We developed quantitative transmission electron microscopy methods within the framework of the project and demonstrated the utility of them in solving problems from materials science. With the help of imaging plates, experimental images from real space (HRTEM) and from reciprocal space (diffraction patterns) were recorded with high accuracy (with one million gray levels). We developed a new method to process both the electron diffraction (ED) patterns and the HRTEM images quantitatively to result in both qualitative and quantitative phase analysis and to index patterns from individual crystal grains. The measured quantities were compared to similar ones (simulated HRTEM images and calculated kinematic diffraction), calculated from structural models. Construction of a structural model for inhomogeneous, complex structures is helped by a computer program also developed in this project. These methods helped us in solving the following problems: development of CNx structures from curved gaphene-sheets; initial stages of reaction between semiconductors (Ge, Si) and metals; structure of airborne soot particles and of volcanic silicates; formation of embedded, isolated Co nanoparticles and the phase selection during their formation; effect of the polarity of SiC on the growth; asymmetry in the nucleation of the intermetallic in Cu/Mg multilayer systems. Or results were presented at international conferences and schools and published in 11 papers in referenced journals (with cumulative impact factor of 27.24)

AlNiGe kao nov namjenski materijal za kontakte na n–GaAs

Al(150 nm)/Ni(30 nm)/Ge(40 nm) layers have been deposited onto n-type GaAs by thermal evaporation. The samples have been annealed for 20 minutes in flowing forming gas H2:N2 (30%:70%). The alloying behaviour of the specimens has been investigated by electron microscope. The contacts show a bilayer structure in the case of as-deposited samples. The top layer is pure Al and the second one is Ni-Ge. The metal-semiconductor interface is sharp. Annealing at 400 °C resulted in the formation of florets on the surface assumed to be AlGe eutectic; meanwhile, randomly distributed pits of size 10 nm have been grown into the GaAs. The samples annealed at 450 °C show bilayer structure. The top layer is pure Ge and the second one consists of Al-Ni(Ge). On samples annealed at 500 °C thick alloyed layer has been found with deep pyramidal pits of size 0.25 µm. The interface region between GaAs and the pits contains substantial amount of Al. Contrary to the published results, I-V (current-voltage) characteristics of the annealed specimens show that the contacts remained rectifying at each applied annealing process. The temperature dependence of parameters evaluated from either current-voltage or capacitance-voltage characteristics prove that the characteristic form of conductance is the anomalous thermionic-field emission.Slojevi Al(150 nm)/Ni(30 nm)/Ge(40 nm) termički su napareni na GaAs n–tipa. Uzorci su otpuštani u plinskoj smjesi H2(30%)+N2(70%) na 400 ◦C, 450 ◦C i 500 ◦C i njihovo legiranje je ispitivano elektronskom mikroskopijom. Suprotno objavljenim rezultatima, I − V krivulje pokazuju da spojevi zadržavaju ispravljačko svojstvo nakon otpuštanja na svim primijenjenim temperaturama. Temperaturna ovisnost parametara koji su bili određeni na osnovi ovisnosti struje o naponu ili kapaciteta o naponu potvrđuju da je vodenje struje posljedica anomalne termionske emisije polja

PALLADIUM BASED CONTACTS TO GaAs AND InP

Au(85nm)/Pd(55nm) and Pd(55nm) metallizations were deposited on GaAs(lOO) and InP(100) substrates. The samples were heat treated in a scanning electron microscope (SEM) equipped with a quadrupole mass spectrometer. The simultaneous observation of the volatile component loss (in situ) by Evolved Gas Analysis (EGA) and the change in surface morphology by SEM during the heart treatment using a heating rate of 30°C/min were carried out. The interaction of the metallization with compound semiconductor substrates was observed after the heat treatment by transmission electron microscopy (TEM) using samples prepared by cross-sectional technique. In the course of the present work a large volatile component (arsenic and phosphorus) loss was observed for the samples coated by single layer metallization (at 410° C for Pd/GaAs and at 580°C for Pd/InP) and two peaks were registered in the case of Au/Pd metallization. In the latter case the cause of the second evaporation peak is the interaction between diffused gold and compound semiconductor. The SEM images of the surfaces demonstrate a significant change of the surface morphology at the singularities of the EGA curves. The grains grown into the semiconductors are shown by the cross-sectional images of the heat treated samples

AlNiGe kao nov namjenski materijal za kontakte na n–GaAs

Al(150 nm)/Ni(30 nm)/Ge(40 nm) layers have been deposited onto n-type GaAs by thermal evaporation. The samples have been annealed for 20 minutes in flowing forming gas H2:N2 (30%:70%). The alloying behaviour of the specimens has been investigated by electron microscope. The contacts show a bilayer structure in the case of as-deposited samples. The top layer is pure Al and the second one is Ni-Ge. The metal-semiconductor interface is sharp. Annealing at 400 °C resulted in the formation of florets on the surface assumed to be AlGe eutectic; meanwhile, randomly distributed pits of size 10 nm have been grown into the GaAs. The samples annealed at 450 °C show bilayer structure. The top layer is pure Ge and the second one consists of Al-Ni(Ge). On samples annealed at 500 °C thick alloyed layer has been found with deep pyramidal pits of size 0.25 µm. The interface region between GaAs and the pits contains substantial amount of Al. Contrary to the published results, I-V (current-voltage) characteristics of the annealed specimens show that the contacts remained rectifying at each applied annealing process. The temperature dependence of parameters evaluated from either current-voltage or capacitance-voltage characteristics prove that the characteristic form of conductance is the anomalous thermionic-field emission.Slojevi Al(150 nm)/Ni(30 nm)/Ge(40 nm) termički su napareni na GaAs n–tipa. Uzorci su otpuštani u plinskoj smjesi H2(30%)+N2(70%) na 400 ◦C, 450 ◦C i 500 ◦C i njihovo legiranje je ispitivano elektronskom mikroskopijom. Suprotno objavljenim rezultatima, I − V krivulje pokazuju da spojevi zadržavaju ispravljačko svojstvo nakon otpuštanja na svim primijenjenim temperaturama. Temperaturna ovisnost parametara koji su bili određeni na osnovi ovisnosti struje o naponu ili kapaciteta o naponu potvrđuju da je vodenje struje posljedica anomalne termionske emisije polja