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Silicon carbide belongs to the wide band gap semiconductor materials, and it is very perspective in the detection of various types of radiation. Another advantage is the commercial availability of high-quality crystalline material required for the preparation of radiation detectors. The 4H-SiC has the band gap energy of 3.23 eV at room temperature, breakdown voltage about 2×10$^6$ Vcm$^{-1}$, carriers saturation velocity of 2×10$^7$ cms$^-$$^1$ and excellent physical and chemical stability. A large band gap energy is advantageous for low leakage current and high radiation tolerance. Despite all the above advantages, fabricated Schottky barrier detectors have certain drawbacks. One of them is the large dispersion of reverse current values, and usually only a small percentage of structures have low currents in the order of pA. For this reason, we have focused on the preparation of SiC MOS (Metal Oxide Semiconductor) structures where the oxide interlayer can be beneficial to achieve lower leakage current and higher breakdown voltage [1, 2].
We have fabricated Ni/Y$_2$O$_3$/4H-SiC structures on 100 $\mu$m thick 4H-SiC epitaxial layers. The Y$_2$O$_3$ layers with three different thicknesses (5, 20 and 30 nm) were deposited by pulsed laser deposition. The wide bandgap (5.6 eV) of Y$_2$O$_3$ and high dielectric constant (14-18) is advantageous for the junction leakage current and increasing breakdown voltage. The quality and thickness of deposited oxide layer was tested with X-ray diffractometry. The circular Ni contacts with different diameters (1 and 2 mm) were deposited on the oxide layers. First, we measured the current-voltage characteristics in both directions and the structures show excellent rectification properties. The forward current analysis shows an increase in the Schottky barrier height from the value about 1.08 eV up to 1.24 eV with oxide thickness, while the reverse current decreases to an average value of about 30 pA/cm$^2$ at -400 V. Radiation detection properties were tested using a triple alpha particle source $^{238}$Pu, $^{239}$Pu, $^{244}$Cm up to a reverse bias of 400 V. The best obtained energy resolution of 17.4 keV FWHM (Full Width at Half Maximum) for 5.8 MeV alpha particles was measured using the detector with a 20 nm oxide layer. This corresponds to a relative value about 0.3%. Despite the best electrical properties of the MOS structures with the thickest oxide layer, the energy resolution was slightly worse with a value of about 25.0 keV (0.43 %). This is because the oxide layer represents the dead layer for alpha particles and increasing its thickness degrades the energy resolution of the detector. However, for other types of radiation such as X-rays or neutrons, the oxide layer thickness shouldn’t be a serious problem.
References: [1] OmerFaruk Karadavut, Ritwik Nag, Josh W. Kleppinger, Gene Yang, Dongkyu Lee, Sandeep K. Chaudhuri, and Krishna C. Mandal “Investigation of Ni/Y2O3/n-4H-SiC metal-oxide-semiconductor structure for high-resolution radiation detection”, Proc. SPIE 12241, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXIV, 1224107 [2] Sandeep K. Chaudhuri; OmerFaruk Karadavut; Joshua W. Kleppinger; Ritwik Nag; Gene Yang; Dongkyu Lee, Krishna C. Mandal “Enhanced Hole Transport in Ni/Y2O3/n-4H-SiC MOS for Self-Biased Radiation Detection”, IEEE Electron Device Letters 43(9) pp.1416-1419
Acknowledgement: This work was partially supported by grants of the Slovak Research and Development Agency Nos. APVV-22-0382, SK-CZ-RD-21-0116, Ministry of Education, Youth and Sports of the Czech Republic No. LU-ASK22147 and of the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences No. 2/0063/24
| Workshop topics | Sensor materials, device processing & technologies |
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