Yaroslav Koshka

Chloride-based CVD growth of silicon carbide for electronic applications.

Chloride-Based CVD Growth of Silicon Carbide for Electronic Applications Henrik Pedersen,* Stefano Leone, Olof Kordina, Anne Henry, Shin-ichi Nishizawa, Yaroslav Koshka, and Erik Janz en Department of Physics, Chemistry and Biology, Link€oping University, SE-581 83 Link€oping, Sweden National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan Department of Electrical and Computer Engineering, Mississippi State University, Mississippi State, Mississippi 39762, United States

Cryogenic and high temperature performance of 4H-SiC vertical junction field effect transistors (VJFETs) for space applications

In this paper, we present an investigation on the different aspects of the performance of a 600V, 3A 4H-SiC vertical-trench junction field effect transistor (VJFET) at cryogenic and high temperatures. Some critical device physics related factors that affect the DC characteristics and switching performance of the device are explored. In particular, the experimental low-temperature performance of 4H-SiC VJFETs (down to 30K or -243/spl deg/C) is presented for the first time to our knowledge.

Photoconductivity in Porous GaN Layers

The first observation of photoconductivity (PC) in porous GaN layers fabricated by surface anodization of 0.6 μm thick GaN layers grown by HVPE on 6H-SiC substrates is reported. PC was studied at room temperature and a strong photoresponse was observed in anodized GaN layers, whereas no photoconduction in initial (not anodized) epitaxial layers was detected. Both the buildup and the decay of the PC in anodized GaN demonstrated exponential behavior with two time constants of 1.8 and 100 s, respectively. PC spectra of anodized GaN showed a steady increase of the photoresponse as the photon energy was increased from 2.5 to 3 eV. Room and low temperature (15 K) photoluminescence studies were also performed on initial and anodized structures. EBIC measurements showed formation of a barrier on the GaN/SiC interface after anodization. Photoresponse in anodized GaN layers is ascribed to a decrease in carrier concentration in the anodized semiconductor.

Effect of HCl addition on gas-phase and surface reactions during homoepitaxial growth of SiC at low temperatures

A complex influence of HCl addition on gas-phase and surface reactions during the low-temperature halo-carbon homoepitaxial growth of 4H-SiC was investigated. The addition of HCl was employed to reduce the undesirable effects of homogeneous gas-phase nucleation leading to formation of silicon clusters in the gas phase. It was established that dissociation of silicon clusters by HCl is efficient even at untraditionally low homoepitaxial growth temperature below 1300 °C. The information about the spatial distribution of this dissociation process along the gas flow direction was obtained. It was established that the influence of HCl is more complicated than the simple model suggesting that the enhanced dissociation of silicon clusters in the gas phase leads to an additional supply of silicon species for the epitaxial growth. While the growth rate does significantly increase at least for some HCl flow rates, complex changes in the effective silicon-to-carbon ratio in the growth zone of the reactor indicate th...

Structure, paramagnetic defects and light-emission of carbon-rich a-SiC:H films

The effect of vacuum annealing on local structure reconstruction, evolution of photoluminescence (PL) and paramagnetic defects in carbon-rich a-Si1−xCx:H films (x=0.7) was studied. Strong enhancement of visible (white-green) PL was observed after annealing in the temperature range of 400–500 °C. Such enhancement was correlated with increasing of the concentration of carbon-hydrogen bonds in Si:CHn accompanied with increase in the fluctuation of the interatomic potential. Complete disappearance of PL, “graphitization” of the carbon precipitates, and a strong increase in the concentration of the paramagnetic states were observed after annealing at 650 °C and above. The enhancement and the degradation of PL after different-temperature treatments are explained by the following competing effects: (1) enhancement of the radiative recombination due to passivation of paramagnetic defects with hydrogen and increase of localization of photoexcited electron-hole pairs due to formation of new Si:CH and (2) enhancem...

Assessment of "Normally On" and "Quasi On" SiC VJFET's in Half-Bridge Circuits

The successful development of the silicon carbide vertical junction field effect transistor (VJFET) has provoked discussion about the role of “normally on” devices in modern power electronics. In this paper we report on the application of trench SiC VJFETs with blocking voltages up to 1000 V and saturated drain currents up to 4 A that have been engineered to exhibit “normally on,” “normally off,” and “quasi-on” operation. “Normally on” is defined as drain current saturation at, or close to, zero gate bias. “Quasi-on” is defined by a zero gate bias drain current significantly reduced from the final saturated value, but still well above the leakage current observed at pinch off. The quasi-on state can be exploited to manage abnormal operation of a pure VJFET-switched half-bridge circuit without resorting to normally off devices. The flexibility afforded by exploiting the safe operating area of the quasi-on VJFET is illustrated with a design example involving a halfbridge circuit.

Gamma and Proton Irradiation Effects on 4H-SiC Depletion-Mode Trench JFETs

4H-SiC vertical depletion-mode trench JFETs were fabricated, packaged, and then irradiated with either 6.8 Mrad gamma from a 60Co source, a 9x1011 cm-2 dose of 4 MeV protons, or a 5x1013 cm-2 dose of 63 MeV protons. 4H-SiC Schottky diodes were also fabricated, packaged and exposed to the same irradiations. The trench VJFETs have a nominal blocking voltage of 600 V and a forward current rating of 2 A prior to irradiation. On-state and blocking I-V characteristics were measured after irradiation and compared to the pre-irradiation performance. Devices irradiated with 4 MeV proton and gamma radiation showed a slight increase in on resistance and a decrease in leakage current in blocking mode. Devices irradiated with 63 MeV protons, however, showed a dramatic decrease in forward current. DLTS measurements were performed, and the results of these measurements will be discussed as well.

Effect of hydrogenation on Al-related photoluminescence in 6H–SiC

Interaction of hydrogen with Al acceptors in SiC is investigated using low-temperature photoluminescence (PL) spectroscopy. Hydrogenation is performed in hydrogen plasma using a standard inductively coupled plasma etching system. Appearance of H-related PL peaks after hydrogenation is accompanied with a significant reduction in relative intensity of Al bound exciton (Al–BE) PL. A gradual quenching of the remaining Al–BE photoluminescence is observed in hydrogenated samples under excitation with above band gap light, resulting in a complete disappearance of Al–BE PL emission. High-temperature annealing completely restores the shape of the PL spectrum to its prehydrogenation form.

Homoepitaxial Growth of 4H-SiC Using CH3Cl Carbon Precursor

The results of the initial experiments with halogenated carbon precursor chloromethane (CH3Cl) for epitaxial growth of 4H-SiC are presented. The growth rate for mirror-like morphology was easily increased up to about 7 µm/hr at C-rich conditions without detectable surface morphology degradation. Further increase of the silane flow resulted in island formation. The growth with the traditional silane-propane system at the same conditions (and optimized Si/C ratio) produced a very different result, with the growth rate decreasing from upstream to downstream, and morphology degradation taking place for much lower growth rate than in CH3Cl growth. Consequently, the epitaxial growth with chloromethane appears to have significantly different kinetics of the gas-phase precursor decomposition and different mechanisms of the surface reactions, which favors the step-flow growth. In addition, these preliminary data indicated that the maximum achievable growth rate corresponding to the good surface morphology may be noticeably larger for the CH3Cl+SiH4+H2 growth system.

Optically induced formation of the hydrogen complex responsible for the 4B0 luminescence in 4H-SiC

Formation of a boron-related defect responsible for the 4B0 emission line in the low-temperature photoluminescence spectrum of 4H SiC has been investigated. The 4B0 luminescence was absent in as-grown epitaxial layers. This line appeared after hydrogenation along with other hydrogen-related lines and disappeared after high-temperature annealing. This is an indication of involvement of hydrogen in formation of the corresponding radiative recombination center. Prolonged excitation of the hydrogenated epitaxial layers with above-band gap light caused not only previously reported enhanced passivation of Al acceptors but also additional strong nonmetastable increase of the 4B0 luminescence due to recombination-enhanced formation of the corresponding defect complex.