Abstract: We present detailed mixed-mode simulations of a DC-DC converter based on 4H-SiC DMOSFETs. The mixed-mode modeling enables the use of complex physics based models for the interface trap occupation and surface mobility that are typical for 4H-SiC devices, and apply them to a practical circuit application such as a DC-DC boost converter. The mixed mode simulations are performed for a reduced DC-DC converter circuit to evaluate the performance of the DMOSFET when it has an inductive load. The current inside the device and its power dissipation during switching are evaluated numerically. Further, the mixed-mode device simulation shows that the majority carriers (electrons) inside the 4H-SiC DMOSFET require a finite time to go from the ON (strongly inverted) to the OFF (depleted) state, thereby causing power dissipation and heating during the turn-off period. The peak power is dissipated in the JFET region of the device which indicates that maximum heat and therefore maximum temperature may be generated there.
Abstract: Starting with the production of Infineon´s first silicon carbide (SiC) Schottky diodes in 2001, a lot of progress was achieved during recent years. Currently, a 3rd generation of MPS (merged pn Schottky) diodes is commercially available combining tremendous improvements with respect to surge current capability and reduced thermal resistance. In this work we present the implementation of SiC switches in power modules and a comparison of these units with the corresponding Si-based power modules. Also the frequency dependence of the total losses of the 1200V configurations using Si-IGBTs or SiC-JFETs as active device is shown, indicating that modules solution with a state of the art SiC JFET outperforms all other options for switching frequencies of 20 kHz and beyond. Additionally a total loss vs. frequency study will be presented. Furthermore, it is show that the switching losses of JFET based modules can be further reduced by reducing the internal distributed gate resistivity.
Abstract: In this paper the system improvements of PV-inverters with SiC-transistors are demonstrated. The basic characteristics of engineering prototypes of normally-off SiC-JFETs and SiC-MOSFETs were measured and their differences in the application are considered. To demonstrate the improvement in PV-inverter performance, a 5 kW single-phase and a three-phase full bridge inverter with normally-off SiC-JFETs were developed at Fraunhofer ISE. Different switching frequencies up to 144 kHz were applied and the impact on production costs and inverter performance was rated under the aspects of an industrial product development. This means, the influences on the efficiency and power density. In this work, a world record in PV-inverter efficiency of 99 % was achieved in a single-phase inverter and for the three-pase inverter, the power density was tripled with respect to commercially available state of the art PV-inverters.
Abstract: The optimal control parameters for semiconductor switches at the development state with new materials and structures are often unidentified. By using those sample switches with a gate control set by investigating one switch only, parasitic influences might lead to increased switching losses in half bridges [1, 2]. The focus of this paper is on an effect at turn on by using for example normally on JFET as high and low side switch. At this an increased current peak might occur which leads to higher switching losses. By adjusting the gate voltage losses can be economized.
Abstract: AlN substrates are produced by Physical Vapor Transport (PVT) growth of AlN bulk single crystals followed by post growth processing of the crystals (calibration, slicing, lapping, and polishing). The AlN substrates are suitable for epitaxial growth. The substrates may be used for development of devices such as ultra violet (UV) light emitting diodes (LEDs) and laser diodes (LDs), Piezo-Electric Transducers, SAW devices, RF Transistors, etc.
Abstract: Free standing AlN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AlN microrods, which evolve from the apex of SiC pyramids grown on the SiC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AlN single crystals with a thickness up to 400 µm and low dislocation density.
Abstract: h-BN layers were deposited on α-SiC substrates by CVD at high temperature (1500-1900°C) using B2H6 and NH3 diluted in Ar. Growth rates were in the 6-10 µm/h range. In all the conditions studied, the BN as deposited layers were found to be translucent to light, some having a light whitish aspect and other a more yellowish one. It was also observed that the deposit was not always adhesive. µ-Raman and TEM characterization showed that the layers were nano-crystalline with crystallite size < 10 nm. The growth rate was found temperature and N/B ratio dependent due to an N limited growth regime which is more pronounced above 1700°C.
Abstract: Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.
Abstract: Amorphous pseudobinary (SiC)1 x(AlN)x thin films have been produced by radio frequency dual magnetron sputtering from bulk SiC and AlN targets. For each target the emission characteristic, i.e. the spatial variation of the deposition rate was determined, in order to predict thickness distribution and spatial composition variation for the (SiC) (AlN) alloy. Impedance spectroscopy shows a high resistivity of the films in the SiC rich region, decreasing significantly towards the AlN rich region.
Abstract: Within the scope of the Harrison’s bond orbital model the spontaneous polarization, high- and low frequency dielectric constants are obtained in an analytical form. Theoretical results are in a reasonable agreement with the experimental data available and the numerical calculations based on the ab initio methods.