Materials Science Forum Vols. 740-742

Abstract: A simplified model for SiC Power diodes has been developed and implemented in Spice simulator in order to get the advantages of a modular and hierarchical structure that can be easily used for modeling of power semiconductor modules. The proposed approach is based on the lumped charge technique. One of the main targets for the proposed model is the implementation of a modeling structure starting from the evaluation and simplification of the semiconductor equations. The paper will show the implementation of the model along with an experimental evaluation of the proposed method.

Abstract: Circuit simulation is of assistance to design and evaluate a power conversion circuit. A compact and accurate power device model is indispensable for obtaining appropriate circuit simulation results. This paper studies the compact equivalent circuit modeling of SiC Schottky Barrier diode (SiCSBD) and evaluates the developed model in turn-off switching operation. Two SiCSBDs having different specification are modeled and evaluated in this paper. The results show that the switching characteristics of SiCSBDs can be modeled with the equivalent circuit, whose configurations and parameters are identified from static I-V and C-V characteristics.

Abstract: Operation of parallel-connected 4H-SiC VJFETs from SemiSouth was measured and modeled using numerical simulations. The unbalanced current waveforms in parallel-connected VJFETs were related to spread in the critical parameters of the device structure and to the influence of the parasitic inductances in the measurement circuit. The physical device structure was reconstructed based on SEM analysis, electrical characterization, and device simulations. The two hypothetical critical design parameters that were studied with respect to spread were the p-gate doping profile (Case 1) and the emitter doping (Case 2). Variation in both parameters could be related to variation in the emitter breakdown voltage, the on-state characteristics, and the threshold voltage of the experimental devices. The switching performance of the parallel-connected JFETs was measured using a single gate driver in a double pulse test and compared with simulations. In both investigated cases a very good agreement between measurements and simulations was obtained. The modeling of the transient performance relies on good reproduction of transfer characteristics and circuit parasitics.

Abstract: We developed a compact model of SiC-IGBT for circuit simulation of power conversion systems under 6.6kV / 100A/cm² bias operation at a few hundred Hz switching frequency. The model includes punch-through effects occurring at the base/buffer surface of the base region. The model allows accurate prediction of switching waveforms and energy loss improvement caused by the punch-through effect (PT-effect).

Abstract: Temperature dependence simulations of forward characteristics for 4H-SiC pin diodes with Shockley-type stacking faults are performed in order to investigate the mechanism of the TEDREC phenomena. The forward voltage drops of both n-type and p-type drift layers at room temperature increase as the length of the Shockley-type stacking fault increases. When the diodes are compared to each other at the same temperature, the differences between the forward voltage drops do not change significantly up to 150 oC, but the differences suddenly narrow in the range from 150 °C to 200 °C. The Shockley-type stacking fault prevents current from flowing at room temperature. The current, however, flows throughout the drifted diode when the temperature is raised.

Abstract: In this work, we studied the effect of surface preparation and substrate temperature during sputter deposition of Schottky contacts on N-GaN/SiC/Si substrates, looking at parameters such as on-resistance, reverse leakage, and contact barrier height. Ti, Ni and Mo were sputtered to form the contacts, and we characterized the I-V curves with the different substrate temperatures during the sputtering as shown in Figure 1. For the Ti Schottky contact, the substrate temperature of 100oC during the sputtering demonstrates the minimum series resistance with Rs about 0.04cm2, while temperatures greater than 3000C increased reverse bias leakage. The Mott-Schottky plot reveals a barrier height of 1.2V for this contact. Results for sputtered Ni contacts using different substrate temperatures will also be presented, as well as the effect of Ar sputter cleaning before contact deposition.

Abstract: Al0.35Ga0.65N/GaN- and Al0.2Ga0.8N/AlN/GaN-heterostructures high electron mobility transistors (HEMTs) with a gate length (LG) varying from 1.2 to 0.08 µm were fabricated on silicon Si(111) substrates using a 3C-SiC transition layer. Metal organic chemical vapour deposition (MOCVD) was used to growth the AlGaN-heterostructures and a low pressure chemical vapour deposition (LPCVD) to create the 3C-SiC(111) transition layer preventing Ga-induced melt back etching and Si-out diffusion. Reduced Al content and an AlN interlayer improved the device performance. The HEMTs with LG=0.08µm had a maximum drain current density of 1.25 A/mm and a peak extrinsic transconductance of 400 mS/mm. A unity current gain cut-off frequency (ƒT) of 180 GHz and maximum frequency (ƒmax) of 70 GHz were measured on these devices.

Abstract: Heteroepitaxial AlGaN/GaN on SiC/Si pseudosubstrate was used to fabricate three-terminal junction devices. Narrow bar and wide bar type active regions were fabricated. The measurement at room temperature showed predicted nonlinear behavior (previously reported about as negative type rectification). Unusual, positive type rectification for two dimensional electron gases was also observed. The electrical characteristics depend on the geometrical configuration of the devices.

Abstract: Gallium Nitride (GaN) is known to provide the opportunity of producing power transistors with remarkable electrical properties, such as low on-state resistance and low switching energies. This paper demonstrates how the use of GaN power transistors along with the possibility of raising the switching frequency can lead to a significant reduction of volume, weight and production costs of a power converter while maintaining high efficiency. A 1 kW resonant LLC converter using 600 V GaN power transistors is presented.