Daniel Donoval

Influence of surface oxidation on plasmon resonance in monolayer of gold and silver nanoparticles

Surface plasmon resonance of gold and silver nanoparticle (NP) layers is investigated by the experiment as well as simulations. Although the good agreement was found for gold NP film, a significant mismatch in the resonance energy for silver NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in silver NPs. As an alternative to the NP size-dependent Drude model, the analysis based on effective medium approximation for refractive index of Ag-Ag2O material system is carried out and compared with the core-shell model. Both Mies model and numerical simulation results illustrate shift of the surface plasmon resonance due to silver NP surface oxidation.Surface plasmon resonance of gold and silver nanoparticle (NP) layers is investigated by the experiment as well as simulations. Although the good agreement was found for gold NP film, a significant mismatch in the resonance energy for silver NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in silver NPs. As an alternative to the NP size-dependent Drude model, the analysis based on effective medium approximation for refractive index of Ag-Ag2O material system is carried out and compared with the core-shell model. Both Mies model and numerical simulation results illustrate shift of the surface plasmon resonance due to silver NP surface oxidation.

Fast 3-D Electrothermal Device/Circuit Simulation of Power Superjunction MOSFET Based on SDevice and HSPICE Interaction

Automated interaction of SDevice and HSPICE for fast 3-D electrothermal simulation based on the relaxation method is designed. The results are compared with device finite element model simulation and a direct method with an equivalent thermal 3-D RC network. The features and limitations of the methods are analyzed and presented. The designed electrothermal simulation based on the relaxation method is developed for Synopsys TCAD Sentaurus environment for decreasing the simulation time for complex 3-D devices. A power vertical superjunction MOSFET under an unclamped inductive switching test of device robustness is used to perform validation of the designed electrothermal simulation.

Advanced Methodology for Fast 3-D TCAD Device/Circuit Electrothermal Simulation and Analysis of Power HEMTs

This paper introduces an advanced methodology for fast 3-D Technology Computer Aided Design (TCAD) electrothermal simulation for the analysis of power devices. The proposed methodology is based on coupling finite element method (FEM) thermal and circuit electrical simulation in a mixed-mode setup. A power InAlN/GaN high-electron mobility transistor (HEMT) is used to perform validation of the designed electrothermal simulation. A new equivalent temperature-dependent nonlinear analytical large signal circuit model of HEMT is proposed. The model is implemented to Synopsys TCAD Sentaurus using compact model interface. The designed electrothermal simulation methodology is developed to shorten the simulation time for complex 3-D devices. This approach combines the speed and accuracy, and couples temperature nonuniformity to the active device electrothermal behavior. The simulation results are compared with the measured data and results of 2-D FEM simulations. The features and limitations of the methods are analyzed and presented.

Self-Heating in GaN Transistors Designed for High-Power Operation

DC and transient self-heating effects are investigated in normally off AlGaN/GaN transistors designed for a high-power operation. Electrical and optical methods are combined with thermal simulations; 2-μs-long voltage pulses dissipating about 4.5 W/mm are applied on four different transistor structures combining GaN or AlGaN buffer on an n-type SiC substrate with or without Ar implantation. Transistors with only 5% Al mass fraction in the buffer show almost a threefold increase in the transient self-heating if compared with devices on the GaN buffer. On the other hand, 2-μs-long pulses were found not to be long enough for the Ar-implanted SiC substrate to influence the device self-heating unless AlGaN composition changes. In the dc mode, however, both the buffer composition and Ar implantation significantly influence the self-heating effect with the highest temperature rise for the transistor having the AlGaN buffer grown on the Ar-implanted SiC. We point on possible tradeoffs between the transistor high-power design and the device thermal resistance.

Revised theory of current transport through the Schottky structure

Abstract A new treatment of the theory describing carrier transport across the rectifying metal-semiconductor interface is presented. Besides the thermionic emission or drift-diffusion mechanisms of current flow, the generation-recombination processes in the analyzed structure have also been taken into account. Our approach is based on the direct solution of Poisson and continuity equations for electrons and holes. This leads to a more general expression for the total current flow through the interface which describes not only the thermionic emission/drift-diffusion current but also the generation-recombination current and injection of holes into the quasi-neutral semiconductor region. The comparison of simulated characteristics based on the approach of Crowell and Sze and on our approach with experimental characteristics measured on a real Schottky structure shows very good agreement of all characteristics in the forward direction and also for a low reverse bias. However, for higher reverse voltages the discrepancy between experimental and simulated characteristics based on the model of Crowell and Sze could be clearly seen while the fit of experimentally measured points by our model is extremely good until the leak current affects the experimental characteristic. This very good correlation was reached due to the generation of electrons and holes within the space charge region which becomes more significant at higher reverse voltages. Generated electrons and holes are separated by an electric field in the analyzed structure. Then the additional hole current is flowing through the interface from semiconductor to metal and the additional electron current flowing through the reference ohmic contact which contributes to the total current.

Near-UV Irradiation Effects on Pentacene-Based Organic Thin Film Transistors

We irradiated Organic Thin-Film Transistors using light sources with peak wavelength in the near-UV spectrum. Organic Thin-Film Transistors have been found very sensitive to near UV rays. Irradiation generates negative trapped charge due to photogeneration, as well as neutral defects, which degrade the mobility and transconductance. We observed noticeable degradation even with 400-nm wavelength, which lies between visible and UV-light. Stronger variations were observed with the shortest wavelength, with a transconductance drop of -85% after 33000-s irradiation with 310 nm UV. We found that the mobility degradation is permanent after storing the devices in vacuum at least for 50 days.

Measurement Systemwith Hall and a Four Point Probes for Characterization of Semiconductors

One of the biggest challenges of communication networks is the video transmission in real time. It requires high demands on the available network capacity and transport mechanisms. Availability of smart mobile devices with batteries, which keep the terminal working for several hours, caused an increased interest in the research of the deployment of video transmission in wireless transmission systems. The presented paper deals with the transmission of video encoded with H.264/AVC (Advanced Video Coding) video coding standard through wireless local area network (WLAN) using the programming environment OPNET Modeller (OM). The test network studied in this work was prepared by combining real and simulated networks, which allows interesting possibilities when working with the OM tools. Such an approach to working with OM allows a detailed video streaming analysis, because the video output was noticeably not only in the form of statistics, but we can see the real impact of transmission failures. Using the OM simulation environment allows to design the transmission systems, which would be difficult to establish in laboratory conditions.

Enhanced permanent degradation of organic TFT under electrical stress and visible light exposure

Abstract We subjected OTFTs to electrical stress under various illumination conditions, in the visible-light range. Negligible intrinsic degradation is observed without stress and light permanent effects of light without stress on OTFT properties are very modest. When light and stress are applied simultaneously, the degradation is much stronger, than stress alone. We found that the acceleration factor is over 2 if blue light is shed on the devices.

Low-energy UV effects on Organic Thin-Film-Transistors

We subjected Organic Thin-Film-Transistors with different gate dielectrics interface treatment to visible light and low energy UV irradiation. Devices with silicon nanoparticles only feature a remarkable temporary charge trapping, regardless the irradiation wavelength. On the contrary, devices without silicon nanoparticles feature temporary trapped charge under visible light, and permanent mobility degradation if they are irradiated with a wavelength shorter than 420nm.

Organic TFT with SiO 2 -parylene gate dielectric stack and optimized pentacene growth temperature

We show that the performances of low cost pentacene-based organic thin-film-transistors can be optimized adjusting the pentacene growth temperature. A performance gain exceeding 10 is obtained if the pentacene is grown with a substrate temperature of 50°C instead 90°C. The saturation drain current is not a monotonic function of the pentacene growth temperature. C-V measurements performed in dark conditions show a negligible hysteresis, but the hysteresis is strongly enhanced if the C-V measurements are performed in light, indicating the presence of photon-activated border traps.