Michał A. Borysiewicz

Photonic structures with grating couplers based on ZnO

The paper presents investigations concerning the design and realization of photonic structures with grating couplers. The first part of the paper deals with basic theoretical information on photonic structures with grating couplers and their application in optoelectronics. The further part presents the results of numerical investigations on photonic structures with grating couplers and shows the influence of geometrical parameters on the effectiveness of the input and output of optic power into and out of this photonic structure. The paper also provides the results of experimental investigations on a wideband gap semiconductor, viz. zinc oxide ZnO, as well as its application in planar waveguide structures and photonic structures with grating couplers.

Ni-Based Ohmic Contacts to n-Type 4H-SiC: The Formation Mechanism and Thermal Stability

The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices. For the n-type SiC, Ni-based metallization is most commonly used for Schottky and ohmic contacts. Many experimental studies have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain the Schottky to ohmic transition for Ni/SiC contacts. In the present review, we summarize the last key results on the matter and post open questions concerning the unclear issues of ohmic contacts to n-type SiC. Analysis of the literature data and our own experimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientation of silicide at the heterointerface (0001)SiC//(013)-Ni2Si. Moreover, we may conclude that only δ-Ni2Si grains play a key role in determining electrical transport properties at the contact/SiC interface. Finally, we show that the diffusion barriers with free diffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics.

Surface Properties of Nanostructured, Porous ZnO Thin Films Prepared by Direct Current Reactive Magnetron Sputtering

In this paper, the results of detailed X-ray photoelectron spectroscopy (XPS) studies combined with atomic force microscopy (AFM) investigation concerning the local surface chemistry and morphology of nanostructured ZnO thin films are presented. They have been deposited by direct current (DC) reactive magnetron sputtering under variable absolute Ar/O2 flows (in sccm): 3:0.3; 8:0.8; 10:1; 15:1.5; 20:2, and 30:3, respectively. The XPS studies allowed us to obtain the information on: (1) the relative concentrations of main elements related to their surface nonstoichiometry; (2) the existence of undesired C surface contaminations; and (3) the various forms of surface bondings. It was found that only for the nanostructured ZnO thin films, deposited under extremely different conditions, i.e., for Ar/O2 flow ratio equal to 3:0.3 and 30:3 (in sccm), respectively, an evident and the most pronounced difference had been observed. The same was for the case of AFM experiments. What is crucial, our experiments allowed us to find the correlation mainly between the lowest level of C contaminations and the local surface morphology of nanostructured ZnO thin films obtained at the highest Ar/O2 ratio (30:3), for which the densely packaged (agglomerated) nanograins were observed, yielding a smaller surface area for undesired C adsorption. The obtained information can help in understanding the reason of still rather poor gas sensor characteristics of ZnO based nanostructures including the undesired ageing effect, being of a serious barrier for their potential application in the development of novel gas sensor devices.

Influence of Carbon Layer on the Properties of Ni-Based Ohmic Contact to n-Type 4H-SiC

Nickel-based contacts with additional interfacial layer of carbon, deposited on n-type 4H-SiC, were annealed at temperatures ranging from 600 to 1000°C and the evolution of the electrical and structural properties were analyzed by I-V measurements, SIMS, TEM, and Raman spectroscopy. Ohmic contact is formed after annealing at 800°C and minimal specific contact resistance of about  Ω cm2 has been achieved after annealing at 1000°C. The interfacial carbon is amorphous in as-deposited state and rapidly diffuses and dissolves in nickel forming graphitized carbon. This process activates interfacial reaction between Ni and SiC at lower temperature than usual and causes the formation of ohmic contact at relatively low temperature. However, our results show that the specific contact resistance as well as interface quality of contacts was not improved, if additional layer of carbon is placed between Ni and SiC.

Hybrid photonics structures with grating and prism couplers based on ZnO waveguides

This paper presents the results of investigations concerning input-output systems of an electromagnetic wave in the visible and near visible spectrum for their application in structures of integrated optics. The input-output structures used in described planar optical waveguides are in a form of prism and grating couplers. The first part of the paper contains numerical analysis of grating couplers aiming at an optimization of their geometrical parameters, strictly — the depth of the grooves in the grating coupler. The second part presents the practical realization, as well as experimental tests of the planar optical waveguide with the hybrid input-output system. As the input system of the electromagnetic wave, a prism coupler was used, and in the case of the output system — a photonic structure with grating coupler was applied. The investigated planar wave guides with the input-output structures were made of a wide energy band gap semiconductor — zinc oxide (ZnO).

Visible and Deep-Ultraviolet Raman Spectroscopy as a Tool for Investigation of Structural Changes and Redistribution of Carbon in Ni-Based Ohmic Contacts on Silicon Carbide

Three samples of 4H polytype of silicon carbide (4H-SiC) covered with the following sequence of layers: carbon/nickel/silicon/nickel/silicon were investigated with micro-Raman spectroscopy. Different thermal treatments of each sample result in differences of carbon layer structure and migration of carbon atoms thorough silicide layer. Two ranges of Raman shift were investigated. The first one is placed between 1000 and 2000 . The main carbon bands D and G are observed in this range. Analysis of the positions of these bands and their intensity ratio enables one to determine the graphitization degree of carbon layer. Additional information about the changes of the carbon layer structure was derived from analysis of 2D band placed around 2700 . Application of deep ultraviolet excitation delivered information about the structure of carbon layer formed on the free surface of silicides and the distribution of the carbon inside the silicide layer.

Room temperature sputter deposited catalyst-free nanowires with wurtzite/zinc blende ZnO superstructure and their application in electromechanical nanogenerators on polymer and paper substrates

Catalyst-free growth of ZnO nanowires using reactive magnetron sputtering at room temperature is reported. We discuss the growth of the nanowires using reactive magnetron sputtering as a function of argon and oxygen flow values changing at a set ratio of 10:2. A transition from nanostructured Zn to nanowire ZnO growth is observed at 20 sccm Ar and 4 sccm O2. Densification and improved alignment of the nanowires is visible for increasing flow values up to 50 sccm Ar and 10 sccm O2. Nanowires exhibit stacking fault regions of zinc blende ZnO in wurtzite ZnO. The regions encompass the whole width of the nanowires and their quantum well behavior is manifested in the photoluminescence spectra. The nanowires were subsequently deposited on paper and PET substrates and electromechanical nanogenerators were fabricated. Manual pressing and depressing of the devices induced voltages of 50 μV and 2 μV for the devices on PET and paper substrates, respectively.

Microstructure Characterization of Si/Ni Contact Layers on n-Type 4H-SiC by TEM and XEDS

Distribution of chemical composition in nickel-based ohmic contacts to n-type 4H-SiC was investigated with XEDS mapping performed on plan-view and cross-sectional TEM samples. Obtained results indicate that local deviations in stoichiometry from that of Ni2Si phase significantly contribute to degradation of surface morphology.

Enhancement of Ru–Si–O/In–Ga–Zn–O MESFET Performance by Reducing Depletion Region Trap Density

In this letter, we investigated the effect of magnetron cathode current (I_c) during reactive sputtering of In-Ga-Zn-O (a-IGZO) channel layer on properties of metal-semiconductor field-effect transistors with Ru-Si-O Schottky gate electrode. One can observe that as I_c increased from 90 to 150 mA channel mobility (μ_ch) and subthreshold swing (S) improved from μch = 7.5 cm²/V·s and S = 580 V/dec to μch = 8.8 cm²/V ·s and S = 420 V/dec, respectively. This enhancement in transistors performance was attributed to the reduction of charge density in the depletion region of Ru-Si-O/In-Ga-Zn-O Schottky contacts, which we assigned to the densification of a-IGZO films fabricated at higher I_c.

Structure of Carbonic Layer in Ohmic Contacts: Comparison of Silicon Carbide/Carbon and Carbon/Silicide Interfaces

The structure of carbonic layer in three samples composed of 4H polytype of silicon carbide and the following sequence of layers: carbon/nickel/silicon/nickel/silicon was investigated with Raman spectroscopy. Different thermal treatment of the samples led to differences in the structure of carbonic layer. Raman measurements were performed with visible excitation focused on two interfaces: silicon carbide/carbon and carbon/silicide. The results showed differences in the structure across carbon film although its thickness corresponds to 8/10 graphene layers.