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Alternative approaches for Preparation of AlN Nanolayers by Atomic Layer Deposition
Dallaev, Rashid ; Krčma, František (oponent) ; Kolařík, Vladimír (oponent) ; Sedlák, Petr (vedoucí práce)
Aluminum nitride (AlN) is a promising semi-conductive material with a wide band gap. Thin films of AlN find implementation in a variety of electronic and optoelectronic devices. First and foremost, the aim of the research presented within the scope of this dissertation is to introduce new precursors into ALD process for deposition of AlN thin films. The proposed precursors are superior to traditional ones either in cost-efficiency or reactivity. A part of the dissertation is devoted to enhancement of the understanding of chemical processes which take place during and after deposition. In this regard, a working solution to improving the chemical composition of the resulting films, as well as ameliorating deficiencies, for instance, oxidization, has been proposed. Another important aspect of this study has to do with a thorough analysis of hydrogen phenomenon in AlN ALD thin films. Hydrogen impurities have been investigated with the use of accurate and advanced techniques belonging to ion-beam analysis (IBA) groups.
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Extended defects in Ga and Al nitrides
Vacek, Petr ; Holec, David (oponent) ; Hospodková,, Alice (oponent) ; Gröger, Roman (vedoucí práce)
III-nitrides crystallize in the hexagonal (wurtzite) structure, whereas the cubic (zincblende, sphalerite) structure is metastable with only slightly higher energy. Their physical properties are strongly affected by the presence of extended defects that are of different kinds in the two structures. In wurtzite III-nitrides, these are primarily threading dislocations, some of which are known to generate deep defect states in the bandgap, through which they affect the electrical and optoelectronic properties of devices. On the other hand, zincblende III-nitrides contain a large density of stacking faults that facilitate local transformations into the more stable wurtzite structure. The aim of this work is to characterize the extended defects in both crystal structures using a combination of electron microscopy, atomic force microscopy, and X-ray diffraction. We demonstrate that (0001)-oriented samples of GaN/AlN and AlN grown on Si (111) substrate by metal-organic chemical vapor deposition contain a large density of threading dislocations. Their Burgers vectors are mostly parallel to the a-direction of the wurtzite lattice, followed by the Burgers vectors parallel to the a+c-direction, whereas the dislocations with Burgers vectors parallel to the c-direction are relatively rare. The probable origin of threading dislocations is discussed according to the type of the film growth. Prismatic stacking faults were found in thin AlN nucleation layers but were not present in the thicker layers. Amorphous layer composed of SiNx and partially of AlN was found at the AlN/Si interface. We propose that this amorphous layer could have a major role in the relief of misfit strain. Analysis of electrical activity of extended defects in AlN was done using electron beam induced current technique. We have found that threading dislocations cause a weak drop of induced current. However, due to their high density and uniform distribution, they have larger impact on electrical properties than V-defects and their clusters. The topographical and crystallographic defects were studied in as-grown and annealed nucleation layers of zincblende GaN grown on 3C-SiC (001) / Si (001) substrate. The sizes of surface features on as-grown samples increase with the thickness of the nucleation layer and are enhanced by annealing. The surface coverage of GaN with the thinnest nucleation layers is reduced after annealing due to diffusion and desorption (or etching by reactor atmosphere). The stacking faults found in GaN near its interface with SiC were mostly of the intrinsic type bounded by Shockley partial dislocations. The origin of these stacking faults was discussed as well as the impact of partial dislocations on the strain relief. Due to the abundance of stacking faults, their interactions were studied in detail. Based on our findings, we have developed a theoretical model of stacking fault annihilation in zincblende GaN films. This model is shown to be able to predict the decrease of the stacking fault density with increasing film thickness.
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Non-Destructive Local Diagnostics of Optoelectronic Devices
Sobola, Dinara ; Pína,, Ladislav (oponent) ; Pinčík,, Emil (oponent) ; Tománek, Pavel (vedoucí práce)
To obtain novel materials for emerging optoelectronic devices, deeper insight into their structure is required. To achieve this, the development and application of new diagnostic methods is necessary. To contribute to these goals, this dissertation thesis is concerned with local diagnostics, including non-destructive mechanical, electrical and optical techniques for examining the surface of optoelectronic devices and materials. These techniques allows us to understand and improve the overall efficiency and reliability of optoelectronic device structures, which are generally degraded by defects, absorption, internal reflection and other losses. The main effort of the dissertation work is focused on the study of degradation phenomena, which are most often caused by both global and local heating, resulting in increased diffusion of ions and vacancies in the materials of interest. From a variety of optoelectronic devices, we have chosen two representative devices: a) solar cells - a large p-n junction device, and b) thin films - substrates for micro optoelectronic devices. In both cases we provide their detailed surface characterization. For the solar cells, scanning probe microscopy was chosen as the principal tool for non-destructive characterization of surface properties. This method is described, and both positive and negative aspects of the methods used are explained on the basis of literature review and our own experiments. An opinion on the use of probe microscopy applications to study solar cells is given. For the thin films, two interesting, from the stability point of view, materials were chosen as candidates for heterostructure preparation: sapphire and silicon carbide. The obtained data and image analysis showed a correlation between surface parameters and growth conditions for the heterostructures studied for optoelectronic applications. The thesis substantiates using these prospective materials to improve optoelectronic device performance, stability and reliability.
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Depozice Al a AlN ultratenkých vrstev na křemíkový a grafenový substrát
Řihák, Radek ; Čech, Vladimír (oponent) ; Mach, Jindřich (vedoucí práce)
Tato diplomová práce se zabývá přípravou a analýzou ultratenkých vrstev hliníku a nitridu hliníku. Vrstvy byly připraveny depozicí z efuzních cel navržených v rámci předchozí bakalářské práce autora. Jejich konstrukce a testování je v práci rovněž zahrnuta. Experimentálně byly zkoumány vlastnosti hliníkových vrstev na nativním oxidu křemíku, křemíku a grafenu. Rovněž je zde popsána příprava nitridu hliníku pomocí dusíkového iontového zdroje.
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CMOS compatible piezoelectric resonator with FET structure for graphene monolayer properties modulation
Gablech, Imrich ; Frank,, Otakar (oponent) ; Husák,, Miroslav (oponent) ; Pekárek, Jan (vedoucí práce)
This work proposes a new structure allowing characterization of graphene monolayer properties under precisely specified conditions. It combines MEMS piezoelectric resonator with Hall Bar/FET structure. This approach allows changing graphene properties separately or together via two methods. The mechanical way is based on induced strain from the resonator which is graphene monolayer situated on. It brings the opportunity to measure graphene properties induced by the changes of mechanical strain and frequency of forced vibrations without the influence from external electric field. The second way uses FET structure to influence graphene monolayer using an electric field from bottom gate. There is no limit to measure concentration in units of ppb in terms of structure design. This approach of fabrication CMOS-compatible and biocompatible tunable frequency-modulated piezoelectric MEMS resonators with graphene monolayer can be very useful in many fields for molecule level detection.
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Alternative approaches for Preparation of AlN Nanolayers by Atomic Layer Deposition
Dallaev, Rashid ; Krčma, František (oponent) ; Kolařík, Vladimír (oponent) ; Sedlák, Petr (vedoucí práce)
Aluminum nitride (AlN) is a promising semi-conductive material with a wide band gap. Thin films of AlN find implementation in a variety of electronic and optoelectronic devices. First and foremost, the aim of the research presented within the scope of this dissertation is to introduce new precursors into ALD process for deposition of AlN thin films. The proposed precursors are superior to traditional ones either in cost-efficiency or reactivity. A part of the dissertation is devoted to enhancement of the understanding of chemical processes which take place during and after deposition. In this regard, a working solution to improving the chemical composition of the resulting films, as well as ameliorating deficiencies, for instance, oxidization, has been proposed. Another important aspect of this study has to do with a thorough analysis of hydrogen phenomenon in AlN ALD thin films. Hydrogen impurities have been investigated with the use of accurate and advanced techniques belonging to ion-beam analysis (IBA) groups.
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Structural Charachterization Of Aln Thin Films Obtained On Silicon Surface By Pe-Ald
Dallaev, Rashid
The aim of this study is to investigate the hydrogen impregnations in AlN thin films deposited using plasma-enhanced atomic layer deposition technique. As of date, there is an apparent gap in the literature regarding the matter of hydrogen impregnation within the AlN layers. Hydrogen is a frequent contaminant and its content has detrimental effect on the quality of resulted layer, which is why it is relevant to investigate this particular contaminant and try to eliminate or at least minimize its quantity. Within the films hydrogen commonly forms amino or imide types of bonds (–NH2, - NH). There is only a handful of analytical methods enabling the detection of hydrogen. This particular study comprises two of them – Fourier-transform infrared spectroscopy (FTIR) and second ion-mass spectrometry (SIMS). XPS analysis has also been included to examine the surface nature and structural imperfections of the grown layer.
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Extended defects in Ga and Al nitrides
Vacek, Petr ; Holec, David (oponent) ; Hospodková,, Alice (oponent) ; Gröger, Roman (vedoucí práce)
III-nitrides crystallize in the hexagonal (wurtzite) structure, whereas the cubic (zincblende, sphalerite) structure is metastable with only slightly higher energy. Their physical properties are strongly affected by the presence of extended defects that are of different kinds in the two structures. In wurtzite III-nitrides, these are primarily threading dislocations, some of which are known to generate deep defect states in the bandgap, through which they affect the electrical and optoelectronic properties of devices. On the other hand, zincblende III-nitrides contain a large density of stacking faults that facilitate local transformations into the more stable wurtzite structure. The aim of this work is to characterize the extended defects in both crystal structures using a combination of electron microscopy, atomic force microscopy, and X-ray diffraction. We demonstrate that (0001)-oriented samples of GaN/AlN and AlN grown on Si (111) substrate by metal-organic chemical vapor deposition contain a large density of threading dislocations. Their Burgers vectors are mostly parallel to the a-direction of the wurtzite lattice, followed by the Burgers vectors parallel to the a+c-direction, whereas the dislocations with Burgers vectors parallel to the c-direction are relatively rare. The probable origin of threading dislocations is discussed according to the type of the film growth. Prismatic stacking faults were found in thin AlN nucleation layers but were not present in the thicker layers. Amorphous layer composed of SiNx and partially of AlN was found at the AlN/Si interface. We propose that this amorphous layer could have a major role in the relief of misfit strain. Analysis of electrical activity of extended defects in AlN was done using electron beam induced current technique. We have found that threading dislocations cause a weak drop of induced current. However, due to their high density and uniform distribution, they have larger impact on electrical properties than V-defects and their clusters. The topographical and crystallographic defects were studied in as-grown and annealed nucleation layers of zincblende GaN grown on 3C-SiC (001) / Si (001) substrate. The sizes of surface features on as-grown samples increase with the thickness of the nucleation layer and are enhanced by annealing. The surface coverage of GaN with the thinnest nucleation layers is reduced after annealing due to diffusion and desorption (or etching by reactor atmosphere). The stacking faults found in GaN near its interface with SiC were mostly of the intrinsic type bounded by Shockley partial dislocations. The origin of these stacking faults was discussed as well as the impact of partial dislocations on the strain relief. Due to the abundance of stacking faults, their interactions were studied in detail. Based on our findings, we have developed a theoretical model of stacking fault annihilation in zincblende GaN films. This model is shown to be able to predict the decrease of the stacking fault density with increasing film thickness.
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Characterization Of Aln Thin Films Deposited On Thermally Processed Silicon Substrates Using Pe-Ald
Dallaev, Rashid
The aim of this work is to study topography and chemical composition of AlN thin films deposited on Si substrates previously exposed to various time of thermal processing using plasma-enhanced atomic layer deposition technique. The samples were heated up to 500 °C for the period of 2 and 4 hours. Chemical composition of wafers and the films obtained are provided by Xray photoelectron spectroscopy (XPS). Surface topography was investigated using atomic force microscopy (AFM).
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Obtaining Thin Films Of Aln By Atomic Layer
Deposition Using Nh3 Or N2h4 As Precursors
Dallaev, Rashid
In this work we used atomic layer deposition (ALD) method to obtain thin films of AlN using tris(diethylamido)aluminum (III) (TDEAA) with hydrazine (N2H4) or ammonia (NH3) as precursors. Elemental analysis of the film deposited by ALD TDEAA /N2H4 at 200 °C showed the presence of carbon impurities ~ 1.4 at%, oxygen ~ 3.2 at.% and hydrogen 22.6 at.%. The atomic concentration ratio of N/Al was ~ 1.3. The residual impurities content with N2H4 was lower than with NH3. In general, it has been confirmed that hydrazine has a more preferable surface thermochemistry than ammonia.
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