Materials Science Forum Vols. 679-680

Abstract: We present overview of achieved results on 4H-SiC avalanche photodiodes (APDs) and arrays. Cost-effective solar-blind optical filter allows achieving high solar photon rejection ratio of more than 106 in combination with more than 40% single photon detection efficiency at 266nm. Three iterations of devices were fabricated and evaluated to compare their optical and electrical properties. Dark count rates and single photon detection efficiencies are the main characteristics compared for these three iterations of device designs.

Abstract: Detectors capable of withstanding high radiation environments for prolonged periods of exposure are essential for the monitoring of nuclear power stations and nuclear waste as well as for space exploration. Schottky diode X-ray detectors were exposed to high dose proton irradiation (1013 cm-2, 50 MeV) and changes in the detection resolution (spectroscopic full width half-maximum) have been observed. Using Deep Level Transient Spectroscopy (DLTS) and the degradation of the electrical characteristics of the diode, we have shown that radiation induced traps located in the upper half of the bandgap have reduced the concentration of carriers.

Abstract: The effects of proton irradiation on uv 4H-SiC single photon avalanche photodiodes (SPADs) are reported. The SPADs, grown by chemical vapor deposition, were designed for uv operation with dark count rates (DCR) of about 30 kHz and single photon detection efficiency (SPDE) of 4.89%. The SPADs were irradiated with 2 MeV protons to a fluence of 1012 cm-2. After irradiation, the I-V characteristics show forward voltage (<1.9 V) generation-recombination currents 2 to 3 times higher than before irradiation. Single photon counting measurements imply generation-recombination centers created in the band gap after irradiation. For threshold voltage ranging from 23 to 26 mV, the 4H-SiC SPAD showed low DCR (<54 kHz) and high SPDE (>1%) after irradiation. The SPADs demonstrated proton radiation tolerance for geosynchronous space applications.

Abstract: 3.3 kV rated 4H-SiC diodes with nickel monosilicide Schottky contacts and 2-zone JTE regions were fabricated on commercial epitaxial wafers having a 34 m thick blocking layer with donor concentration of 2.2×1015 cm-3. The diodes were fabricated with and without additional field stop rings to investigate the impact of practically realizable stopper rings on the diode blocking characteristics. The field stop ring was formed by reactive ion etching of heavily doped epitaxial capping layer. The diodes with field stop rings demonstrated significantly higher yield and reduction of reverse leakage current. The diodes demonstrated blocking voltages in excess of 4.0 kV and very low change of leakage current at ambient temperatures up to 200 °C.

Abstract: Zener voltages of the fabricated SiC Zener diodes with various nitrogen concentrations in the range from 7×1017 to 5×1019 cm-3 are 17 to 87 V, and decreased with an increase in the nitrogen concentration. Furthermore, in a chopper circuit using SiC Zener diodes for SiCGT gate protection, the commutated current decreases slowly even though cathode current falls rapidly, and the SiCGT gate is protected from surge voltage by SiC Zener diode. Moreover, the value of Zener voltage after the operation was the same as that before half bridge operation at 47 V.

Abstract: This paper focuses on UV-photodetector simulation. The calculus method description and the physical equations which occur in this model are presented as well as the UV-photodetector structure (p+n--n+ diode). Based on the Finite Element Method the electrical part solves the continuity and Poisson equation, and the optical part solves by Maxwell’s equation, FDTD [1]. Simulation works point out the influence of the p+-type layer on the electrical characteristics such as the current densities versus reverse bias. Indeed, simulation results show the current density increase with the decrease doping concentration or the p+-type layer thickness.

Abstract: Avalanche diodes have been fabricated on 4H-SiC substrate. These diodes show an abrupt avalanche voltage of about 59 V which corresponds to the calculated theoretical one using our previously determined impact ionization coefficients. This avalanche voltage increases by as small as 3.7 mV/K over the investigated temperature range (150K-420K).

Abstract: The dependence of the reverse current of 3C-SiC p+-n diodes on the temperature and on the reverse bias is measured and a model based on thermally-assisted tunneling is proposed to explain the dominating mechanism responsible for the leakage current. Taking into account an additional ohmic shunt resistance, the experimental reverse characteristics and thermal barrier heights B can sufficiently be reproduced.

Abstract: 4H-SiC Schottky Barrier Diodes (SBDs) with remarkable electrical performance have been fabricated and characterised. A barrier height about 1.64V and an ideality factor close to 1 are extracted from the forward characteristics measured at several temperatures. These essential Schottky contact parameters are observed to be constant with temperature. A temperature probe with a simple and innovative scheme is designed and applied. The probe uses SiC SBDs as temperature sensor in the 20-4000C range, with measured sensitivities varying from 1.3 mV/K to 2.8 mV/K. The probe is meant to monitorize the temperature inside the furnaces, in the cement industry.

Abstract: This paper reports long-term electrical results from two 6H-SiC junction field effect transistors (JFETs) presently being tested in Low Earth Orbit (LEO) space environment on the outside of the International Space Station (ISS). The JFETs have demonstrated excellent functionality and stability through 4600 hours of LEO space deployment. Observed changes in measured device characteristics tracked changes in measured temperature, consistent with well-known JFET temperature-dependent device physics.