Mietek Bakowski

Measurements of failure phenomena in inductively loaded multi-cathode GTO thyristors

The free-carrier absorption (FCA) technique is used for mapping of the carrier content in a dual-cathode gate turn-off thyristor (GTO) at different stages of the turn-off cycle. The FCA technique outputs 3-D maps based on 2-D measurements of local carrier concentration. The measurements are time resolved, thus making a transient response converted into a corresponding sequence of carrier maps. The dual-cathode device is shown to be sufficient for determining the transient behavior in a multicathode structure. The destruction mechanism and reasons for turn-off failure are investigated. The GTO device is inductively loaded and asymmetrically gate contacted in order to emulate a realistic mode of operation. The gate-driving conditions are altered, and the importance of the turn-off gain for turn-off failure is established. The case of equal ON-state cathode currents in both segments is particularly highlighted. The influence of snubber circuits is also discussed. >

Foreword Special Issue on Wide Bandgap Power Switching Devices for Energy Efficiency and Renewable Energy Integration

Wide bandgap (WBG) semiconductors, especially silicon carbide (SiC) and gallium nitride (GaN), promise transformational advances in electrical power systems, with increased power conversion efficiency for transportation and renewable energy utilization. Compared with the semiconductor silicon, SiC and GaN materials offer significantly higher electrical and thermal conductivities, increased avalanche breakdown field strength, and improved ruggedness under extreme environmental operating conditions. These basic material properties translate into more compact and lightweight power conversion systems with significant energy savings, much improved signal sensing and transmission characteristics, and longer operating life in the field.

Surface states characterization and simulation of Type-II In(Ga)Sb quantum dot structures for processing optimization of LWIR detectors

Quantum structures base on type-II In(Ga)Sb quantum dots (QDs) embedded in an InAs matrix were used as active material for achieving long-wavelength infrared (LWIR) photodetectors in this work. Both InAs and In(Ga)Sb are narrow band semiconductor materials and known to possess a large number of surface states, which apparently play significant impact for the detector’s electrical and optical performance. These surface states are caused not only by material or device processing induced defects but also by surface dangling bonds, oxides, roughness and contaminants. To experimentally analyze the surface states of the QD structures treated by different device fabrication steps, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. The results were used to optimize the fabrication process of the LWIR photodetectors in our ongoing project. The dark current and its temperature dependence of the fabricated IR photodetectors were characterized in temperature range 10 K to 300 K, and the experiment results were analyzed by a theoretic modeling obtained using simulation tool MEDICI.