Papers by Author: Yaroslav Koshka

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Authors: Bharat Krishnan, Joseph Neil Merrett, Galyna Melnychuk, Yaroslav Koshka
Abstract: In this work, the benefits of the low-temperature halo-carbon epitaxial growth at 1300oC to form anodes of 4H-SiC PiN diodes were investigated. Regular-temperature epitaxial growth was used to form an 8.6 μm-thick n-type drift region with net donor concentration of 6.45x1015 cm-3. Trimethylaluminum doping, in situ during blanket low-temperature halo-carbon epitaxial growth, was used to form heavily doped p-type layers. Forward I-V characteristics measured from diodes having different anode areas indicated that the new epitaxial growth technique provides anodes with low values of the series resistance, even without contact annealing. At room temperature, a 100 μm-diameter diode had a forward voltage of 3.75 V at 1000A/cm² before annealing and 3.23 V after annealing for 2 min at 750°C. The reverse breakdown voltage was more than 680 V (on average) in the devices without edge termination or surface passivation.
Authors: Bharat Krishnan, Siva Prasad Kotamraju, Galyna Melnychuk, Neil Merrett, Yaroslav Koshka
Abstract: Low-temperature halo-carbon homoepitaxial growth is suitable for selective epitaxial growth of 4H-SiC using SiO2 mask. A possibility of achieving high values of doping in combination with the selective growth makes it an alternative to ion implantation for selective doping in SiC. In this work, TMA doping in situ during a blanket low-temperature epitaxial growth was utilized to produce heavily Al doped SiC layers for Ohmic contact formation to p-type SiC. Nearly featureless epilayer morphology with Al atomic concentration exceeding 3x1020 cm-3 was obtained after growth at 13000C with the growth rate of 1.5 µm/hr. Ni TLM contacts with a thin adhesion layer of Ti were formed. The as-deposited metal contacts were almost completely Ohmic even before annealing. The specific contact resistance of 2x10-2 Ohm-cm2 and 6x10-5 Ohms-cm2 was achieved without and with contact annealing respectively. The resistivity of the epitaxial layers better than 0.01 Ohm cm was measured for Al atomic concentration of 2.7x1020 cm-3.
Authors: Michael S. Mazzola, Jeff B. Casady, Neil Merrett, Igor Sankin, W.A. Draper, D. Seale, V. Bondarenko, Yaroslav Koshka, J. Gafford, R. Kelly
Authors: Galyna Melnychuck, Yaroslav Koshka, S. Yingquan, Michael S. Mazzola, C.U. Pittman
Authors: Sashi Kumar Chanda, Yaroslav Koshka, Murugesu Yoganathan
Abstract: A room temperature PL mapping technique was applied to establish the origin of resistivity variation in PVT-grown 6H SiC substrates. A direct correlation between the native defect-related PL and resistivity was found in undoped (V-free) samples. In vanadium-doped samples with low vanadium content, the resistivity showed a good correlation with the total PL signal consisting of contributions from both vanadium and native point defects. Well-known UD1 and UD3 levels were revealed by low-temperature PL spectroscopy. Some correlation was observed between these low-temperature PL signatures and the resistivity distribution.
Authors: Hrishikesh Das, Galyna Melnychuk, Yaroslav Koshka
Abstract: Dislocations were investigated in the halo-carbon low-temperature epitaxial growth and low-temperature selective epitaxial growth (LTSEG) conducted at 13000C. The origin of triangular defects was investigated in low-temperature epilayers grown at higher growth rates with HCl addition. Due to the conversion of substrates’ basal plane dislocations (BPD) into threading dislocations, the concentration of BPDs was about an order of magnitude lower than the concentration of threading dislocations at moderate growth rates. An additional order of magnitude conversion of BPDs into threading dislocations was observed at higher grow rates achieved with HCl addition. In LTSEG epilayers, dislocation concentration away from the mesa walls was comparable to the blanket (i.e., regular non-selective) growth. High concentrations of BPDs were found only at mesa edges located on the “upstream” side with respect to the step-flow direction. No substrate defects could be traced to the triangular defects. Instead, the disturbances causing the triangular defect generation are introduced during the epitaxial process.
Authors: Lin Cheng, Janna R. B. Casady, Janice Mazzola, Jeff B. Casady, Yaroslav Koshka, V. Bondarenko
Authors: Siva Prasad Kotamraju, Bharat Krishnan, Franziska Christine Beyer, Anne Henry, Olle Kordina, Erik Janzén, Yaroslav Koshka
Abstract: A reduced growth pressure (down to 10 Torr) was employed for the low-temperature chloro-carbon epitaxial growth. More than two times lower H2 flow rate became possible. The optimal input H2/Si and C/Si ratios were also lower. A significant reduction of the net free donor concentration resulted from the use of the low pressure, delivering partially compensated epilayers with the net free donor concentration below 7x1013 cm-3. Deep levels were characterized in the low-temperature epilayers for the first time. No Z1/2 or EH6/7 centers could be detected by DLTS. No strong D1 photoluminescence signature was observed. The high purity of the obtained epitaxial layers made it possible to use the low-temperature chloro-carbon epitaxial growth to fabricate drift regions of Schottky diodes for the first time. Promising values of the reverse breakdown voltage and the leakage current were obtained from the fabricated devices.
Authors: Bharat Krishnan, Yaroslav Koshka
Abstract: Recombination-induced passivation (RIP) experiments were conducted on p-type SiC after plasma treatment in deuterium. Higher sensitivity of SIMS to deuterium allowed us to confirm that recombination-induced athermal migration of hydrogen is indeed a driving mechanism for the RIP phenomenon. Hydrogen (or deuterium) athermally migrates from the plasma-induced hydrogen- or deuterium-reach near-surface layer down to more than a micron in depth, which under certain conditions creates a sufficiently thick layer of the n-type conductivity in the originally ptype epilayer. Thermal admittance spectroscopy was applied to investigate the defect levels in the top portion of the bandgap of the RIP-induced n-type layer. A few different levels located close to the conduction band of the originally p-type material were investigated.
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