Тонкі плівки оксиду диспрозію, утворені при швидкому термічному відпалі на пористих підкладках SiC

In this paper, we consider the effect of rapid thermal annealing (RTA) on the properties of Dy2O3 film formed on the surface of a substrate with a por-SiC/SiC structure. The atomic composition of the films under study was analyzed as a function of the RTA time. It is shown that the RTA method makes it possible to obtain thin Dy oxide films with a composition close to the stoichiometric one. In this case, an increase in the RTA time leads to improving the quality of film-substrate interface and increasing the optical transmission of Dy2O3/por-SiC/SiC structureУ цій роботі розглянуто вплив швидкого термічного відпалу (ШТВ) на властивості плівки Dy2O3, що утворюється на поверхні підкладки зі структурою por-SiC/SiC. Атомний склад досліджуваних плівок аналізували як функцію часу ШТВ. Показано, що метод ШТВ дозволяє отримувати тонкі плівки оксиду диспрозію зі складом, близьким до стехіометричного. У цьому випадку збільшення часу ШТВ призводить до поліпшення якості межі поділу плівка-підкладка і до збільшення оптичного пропускання структури Dy2O3/por-SiC/SiC

Comparison of properties inherent to thin titanium oxide films formed by rapid thermal annealing on SiC and porous SiC substrates

The comparative analysis of optical characteristics inherent to TiO2/SiC and TiO2/por-SiC/SiC structures has been performed. It has been shown that, in these structures regardless of the substrate structure, formation of TiO2 layers with approximately the same width 60 nm takes place. In this case the TiO2 film composition is close to the stoichiometric one. At the same time, the presence of an additional porous layer in the TiO2/por-SiC/SiC structure leads to blurring the oxide film – substrate interface but promotes an increase in the intensity of the Raman scattering signal from the oxide film

Ohmic contacts to Hall sensors based on n-InSb-GaAs(i) heterostructures

We consider ohmic contacts to the n-InSb epitaxial layers grown on a semi-insulating GaAs substrate. The ohmic contacts are formed through titanium metallization with subsequent gilding. Using the structural (AFM and XRD) and analytical (AES) techniques, we showed that thermal annealings at Т = 300 °С (for 60 s) and 360 °С (for 30 s) do not change the phase composition of the metallization. This ensures thermal stability of the contacts and Hall sensors made on the basis of Au–Ti–n-InSb–GaAs(i) structures

Role of dislocations in formation of ohmic contacts to heavily doped n-Si

We present experimental results concerning a high density of structural defects (in particular, dislocations) in the near-contact region of heavily doped n-silicon. They appear in the course of firing Au Pd Ti Pd -Si n ohmic contact at 450С for 10 min in a vacuum of ~10 Pa⁻⁴ . These defects lead to appearance of metal shunts that determine the current flow mechanism in these ohmic contacts. The calculated and experimental temperature dependences of contact resistivity, ρс(Т), are in good agreement. It is shown that ρс increases with temperature. This is characteristic of a model of ohmic contacts with a high dislocation density in the near-contact region of semiconducto

Development of high-stable contact systems to gallium nitride microwave diodes

High-stable heat-resistant low-resistance contact systems with diffusion barriers involving quasi-amorphous TiBx layers are suggested and studied. We have performed the structural and morphological investigations along with studies of Auger concentration depth profiles in the contacts both before and after rapid thermal annealing. It is found that the Au−TiBx−Al−Ti−GaN contact layers with diffusion barriers retain both a layered structure of the contact metallization and the value of contact resistivity practically unchanged up to the temperature Т ≈ 700 ºС. At the same time, the layered structure of the metallization in standard Au−Ti−Al−Ti−GaN contact systems breaks down at such rapid thermal annealing. It is shown that the contact metallization of both types demonstrates the tunnel current flow mechanism in the temperature range 225−335 K, whereas the current flow mechanism is thermionic in the range 335−380 K, the Schottky barrier height being ~0.16 eV. For the best samples under consideration, the contact resistivity was no more than 10⁻⁶ Ohm∙cm²

The features of temperature dependence of contact resistivity of Au-Ti-Pd₂Si-p⁺ ₋Si ohmic contacts

We consider the features of formation of Au-Ti-Pd ohmic contacts to p⁺₋Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 °С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metal-Si interface

Investigation of resistance formation mechanisms for contacts to n-AlN and n-GaN with a high dislocation density

We studied temperature dependences of the resistivity, Pc(T) , of Pd-Ti-Pd-Au ohmic contacts to wide-gap semiconductors n - GaN and n - AlN with a high dislocation density. BothPc(T) curves have portions of exponential decrease, as well as those with very slight Pc(T) dependence at higher temperatures. Besides, the Au-Pd-TiPd-n-GaN contacts have a portion of Pc(T) flattening out in the low-temperature region. This portion appears only after rapid thermal annealing (RTA). In principle, its appearance may be caused by preliminary heavy doping of the near-contact region with a shallow donor impurity as well as doping in the course of contact formation owing to RTA, if the contact-forming layer involves a material atoms of which serve as shallow donors in III N compounds. The obtained Pc(T) dependences cannot be explained by the existing mechanisms of current transfer. We propose other mechanisms explaining the experimental Pc(T) curves for ohmic contacts to n - GaN and n -AlN

Mechanism of current flow and temperature dependence of contact resistivity in Au-Pd-Ti-Pd-n⁺ -GaN ohmic contacts

We present the results of structural and morphological investigations of interactions between phases in the layers of Au-Pd-Ti-Pd-n⁺-GaN contact metallization that appear at rapid thermal annealing (RTA). It is shown that formation of ohmic contact occurs in the course of RTA at Т = 900°C due to formation of titanium nitride. We studied experimentally and explained theoretically the temperature dependence of contact resistivity ρс(Т) of ohmic contacts in the 4.2-380 K temperature range. The ρс(Т) curve was shown to flatten out in the 4.2-50 K range. As temperature grew, ρс decreased exponentially. The results obtained enabled us to conclude that current flow has field nature at saturation of ρс(Т) and the thermofield nature in the exponential part of ρс(Т) curve

Thermomagnetic studies of thermoexfoliated graphite-transition metal composites

Thermal stability and magnetic susceptibility of thermoexfoliated graphite-metal (TEG-Me) composites have been investigated in the temperature range 300-850 K. The TEG-Me (Co, Ni) composites have been produced by the metal cation reduction in aqueous medium with sodium tetrahydroborate. The structure and phase composition of the products was characterized using X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectrometry. The results of these investigations show that the metal in the green composites must exist in the bound state as Me—B and Me—H. The gradual heating (up to 850 K) or annealing (at 825 K) of the TEG-Me composites results in the appearance of ferromagnetic properties. Thermal cycling of TEG-Me composites results in a decreased magnetic susceptibility due to oxidation of metallic particles

Thermoexfoliated graphite — transitional metal nanocomposites

Composite materials (CM) have been obtained by chemical deposition of metal on graphite surface. It has been shown that TEG-nanoscaled transition metal CM can be prepared both by long-term salt decomposition on TEG surface and simultaneous reduction in hydrogen flow and by preliminary salt decomposition to metal oxide by thermal shock at high temperature. The application of "thermal shock" regime at the salt decomposition stage and metal oxide formation has been shown to result in metal particle formation possessing the size ten fold smaller than that in a case of "direct reduction". The metal particle size distribution obeys Gauss law and practically does not depend on metal component content.Путем химического осаждения металла на поверхность графита получены композитные материалы (КМ). Показано, что КМ, содержащие терморасширенный графит (ТРГ) и наночастицы переходного металла, можно получить как путем длительного разложения соли на поверхности ТРГ с одновременным восстановлением в токе водорода, так и путем предварительного разложения соли до оксида металла в режиме высокотемпературного термоудара. Показано, что применение режима термоудара на стадии разложения соли и образования оксида металла позволяет получить частицы металла на порядок меньшего размера, чем в случае "прямого восстановления". При этом распределение частиц металла по размеру соответствует закону Гаусса и практически не зависит от содержания металлического компонента.Шляхом хімічного осадження металу на поверхню графіту одержано композитні мaтepiaли (КМ). Показано, що КМ, які містять терморозширений графіт (ТРГ) та наночастинки перехідного металу, можна одержати як шляхом тривалого розкладу солі на поверхні ТРГ з одночасним відновленням у потоці водню, так і шляхом попереднього розкладу солі до оксиду металу в режимі високотемпературного термоудару. Показано, що застосування режиму термоудару на стадії розкладу солі та утворення оксиду металу дозволяє одержати частинки металу на порядок меншого розміру, ніж у випадку "прямого відновлення". При цьому розподіл частинок металу за розміром відповідає закону Гаусса і практично не залежить від вмісту металевого компоненту