Materials Science Forum Vols. 778-780

Abstract: Among the different ways to improve the performances of light harvesting inside solar cells, multilayer configuration can be used. The bandgap of each single layer will contribute to absorption in a well defined wave-lengths range, enhancing the overall performances. Here, we investigate such performances in the case of solar cells made by two layers: a silicon one, and a SiC-based layer, and show the increasing of electrical working by means of computer simulations. These simulations are based on Finite Difference Time Domain (FDTD) for the optical calculations, on one side, and the Finite Element Method (FEM) for the electrical ones, on the other. The main goal is to show the enhancement of the electrical performances in heterostructure solar cells. In this paper, we investigate the influence of each different structure on the optical and electrical response. Our results show the influence of the device structures, in particular, the enhancement of the UV-ligth absorption inside the solar cell. Moreover, the difference structures allow us to show an improvement in the harvesting charge carrier by the heterojunction.

Abstract: MOS capacitor devices based on silicon carbide (SiC) are largely used as hydrogen detectors in high temperature and chemically reactive environments. A SiC MOS capacitor structure used as hydrogen sensor is analyzed by extensive simulations. The sensitivity to hydrogen detection, stability to temperature variation and dependence on interface states concentration are evaluated. The effects of structure parameters on sensors performance are also investigated. Results show that the oxide layer type and thickness and the SiC polytype have a significant influence on the detectors performance. The proposed optimum structure for high temperature hydrogen detection is based on 3C-SiC substrate and 10nm TiO₂ layer. In accordance with the simulations results, three types of masks are designed for the fabrication of SiC MOS capacitor structures.

Abstract: High temperature gas sensors for the detection of harmful gases under extreme conditions have been demonstrated. Here, we show the detection and selective response of two SiC based MIS sensor structures with HfO₂ and TiO₂ high κ dielectric layers to two different hydrogen containing gases. The structures utilise a Pt catalytic gate contact and a high-κ dielectric that was grown on a thin SiO₂ layer, which was thermally grown on the Si face of epitaxial 4H SiC. The chemical characteristics of MIS capacitors have been studied in N₂, O₂, H₂ and CH₄ ambients at 573K. The data show a positive flatband voltage shift for oxygen and methane with respect to the nitrogen baseline, whilst hydrogen shows a negative shift. The response for the TiO₂ based sensor is significantly larger than that of the HfO₂ based device for hydrogen, enabling discrimination of gases within a mixture.

Abstract: A partially electrically isolated package with a gold wire and fully isolated solution with a metallic piston, respectively, are designed and tested for high temperature sensors (400°C) based on SiC Schottky barrier diodes (SBD). Electrical behavior and sensor performance are very close for both packaging solutions. The stress due to contact pressure and higher cost are some disadvantages for pressure contact technology.

Abstract: Gas sensitive silicon carbide field effect transistors with nanostructured Ir gate layers have been used for the first time for sensitive detection of volatile organic compounds (VOCs) at part per billion level for indoor air quality applications. Formaldehyde, naphthalene, and benzene have been used as typical VOCs in dry air and under 10% and 20% relative humidity. A single VOC was used at a time to study long-term stability, repeatability, temperature dependence, effect of relative humidity, sensitivity, response and recovery times of the sensors.

Abstract: High Speed Rail (HSR) is expanding rapidly in the whole world in this decade. Almost all the high-speed trains are fed by high-voltage AC and are equipped with several large motors. In addition, High-speed trains have a strict restriction for both mass and size. Thus, HSR needs power semiconductors that can handle high-voltage and giant current. In addition, EMC problems become larger in these days, thus higher speed of switching is expected. From simple silicon diodes in 1960s, thyristors, GTO thyristors, IGBTs and until new wide gap devices such like SiC, the progress of power semiconductor and cooling system directly pulls the performance of high-speed rolling stock. In some cases, fixed installations for HSR are equipped with flexible AC transmission systems (FACTS) such as static VAR compensators (SVC), also.

Abstract: The present status of the development and commercialization of SiC and GaN power devices for power electronics applications is presented. The technology obstacles and needs as well as future trend in these power devices are also discussed.

Abstract: The message of this paper is that the silicon carbide power transistors of today are good enough to design converters with efficiencies and switching speeds beyond comparison with corresponding technology in silicon. This is the time to act. Only in the highest power range the devices are missing. Another important step towards high powers is to find new solutions for multi-chip circuit designs that are adapted to the high possible switching speeds of unipolar silicon carbide power transistors.

Abstract: Advanced high-voltage (≥10 kV) silicon carbide (SiC) devices described in this paper have the potential to significantly impact the system size, weight, high-temperature reliability, and cost of modern variable-speed medium-voltage (MV) systems such as variable speed (VSD) drives for electric motors, integration of renewable energy including energy storage, micro-grids, traction control, and compact pulsed power systems. In this paper, we review the current status of the development of 10 kV-20 kV class power devices in SiC, including MOSFETs, JBS diodes, IGBTs, GTO thyristors, and PiN diodes at Cree. Advantages and weakness of each device are discussed and compared. A strategy for high-voltage SiC power device development is proposed.

Abstract: In order for wide bandgap semiconductor power devices to be practical use in various power electronics applications, a 2in1 600V75A power package with a 200 degree Celsius heat resistance was newly developed on the premise of mass production. This package designed to specify a low inductance of less than 24nH enables SiC and GaN-based devices to be driven with a high slew rate up to 5kA/us under hard-switching condition. Furthermore, this package encapsulated by a epoxy resin of a high heat resistance and equipped with thick Cu heat spreader allow these power devices to be driven up to 200 degree Celsius and dissipate heat in large quantities (thermal resistance R_th,jc: 0.6K/W), which is found to make cooling heat sink simplified. We introduced 50ASiC-MOSFET in this package, and verified the operation on a power conditioner for Solar Photovoltaic cells up to 4kW output. A high power conversion efficiency of 97.7% was measured by our SiC power packages on downsized cooling heat sink in 1/4 volume, which was more efficient than Si-IGBT module by 1.5%.