Characterization of tungsten–nickel simultaneous Ohmic contacts to p- and n-type 4H-SiC

Ohmic contacts to p- and n-type 4H-SiC using refractory alloyed W:Ni thin films were investigated. Transfer length measurement test structures to p-type 4H-SiC (NA = 3 × 1020 cm−3) revealed Ohmic contacts with specific contact resistances, ρc, of ~10−5 Ω cm2 after 0.5 h annealing in argon at temperatures of 1000 °C, 1100 °C, 1150 °C, and 1200 °C. Contacts fabricated on n-type 4H-SiC (ND = 2 × 1019 cm−3) by similar methods were shown to have similar specific contact resistance values after annealing, demonstrating simultaneous Ohmic contact formation for W:Ni alloys on 4H-SiC. The lowest ρc values were (7.3 ± 0.9) × 10−6 Ω cm2 for p-SiC and (6.8 ± 3.1) × 10−6 Ω cm2 for n-SiC after annealing at 1150 °C. X-ray diffraction shows a cubic tungsten–nickel–carbide phase in the Ohmic contacts after annealing as well as WC after higher temperatures. Auger electron spectroscopy depth profiles support the presence of metal carbide regions above a nickel and silicon-rich region near the interface. X-ray energy dispersive spectroscopy mapping showed tungsten-rich and nickel-rich regions after annealing at 1100 °C and above. W:Ni alloys show promise as simultaneous Ohmic contacts to p- and n-SiC, offering low and comparable ρc values along with the formation of WxNiyC.

Source:IOPscience
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Features of the formation of non-vertical profiles on the surface of 4H-SiC by the reactive-ion etching

The features of the formation of non-vertical profiles on 4H-SiC by reactive-ion etching (RIE) using various masking coatings are studied. The formation of 4H-SiC mesa structures was carried out using automated airlock reactive-ion etching and plasma etching system "Caroline PE 15" with the ICP-source of plasma in a gas mixture of SF6, O2 and Ar. Using photoresist AZ4533 as a mask, mesa structures with a wall inclination angle of more than 130° were obtained at the etching rate of 4H-SiC was ~0.5 μm/min. The developed technology of dry etching can be further used in the preparation of avalanche photodiodes or power electronics devices.

Source:IOPscience
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Defects in low-energy electron-irradiated n-type 4H-SiC

The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation increased the DLTS signals of the intrinsic defects Z1/2 and EH6/7 and introduced the frequently observed defects EH1 and EH3. After the M-center is annealed out at about 650 K without bias and at about 575 K with bias applied to the sample during the annealing process, a new bistable defect in the low temperature range of the DLTS spectrum, the EB-center, evolves. Since low-energy irradiation affects mainly the carbon atoms in SiC, the M-center and the newly discovered EB-center are most probably carbon-related intrinsic defects.

Source:IOPscience
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Simulation of conventional bipolar logic technologies in 4H-SiC for harsh environment applications

Silicon carbide (SiC) is a wide bandgap semiconductor that is inherently capable of operation in unforgiving environments such as high temperatures and radiation. Currently, the control circuitry for SiC based power devices and sensors are silicon based, limiting the overall efficiency of the system in such environments. 4H-SiC integrated circuits, based on different conventional logic technologies, have been investigated in the past using different device structures, by various research groups. This paper presents a thorough investigation of conventional bipolar logic technologies in 4H-SiC simulated across a wide range of temperatures (300–773 K) and power supply voltages (7–17 V). Unlike previous studies, this paper evaluates different technologies using the same device structure in the simulation, to highlight the true merits of each logic technology. The stable performance of all the studied logic technologies in SiC validates the potential of 4H-SiC ICs in small scale logic applications.

Source:IOPscience
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Fully implanted vertical p–i–n diodes using high-purity semi-insulating 4H–SiC wafers

The fabrication of a fully ion-implanted vertical p–i–n diode using high-purity semi-insulating 4H–SiC substrate has been demonstrated for the first time. The intrinsic region is the wafer itself with a thickness of 350 µm. The anode and cathode are obtained by doping the front and back wafer surfaces with implanted Al⁺ and P⁺ ions, respectively, with concentrations of about 10²⁰ cm⁻³. The electrical activation of the implanted dopants is obtained by microwave heating the samples up to 2100 °C for 30 s. At ±100 V the on and off state current ratio is in the order of 10⁴. Forward saturation current is five orders larger than it would be if controlled by the series resistance of the thick HPSI 4H–SiC intrinsic region.

Source:IOPscience
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