Speaker
Description
Silicon carbide (SiC) is a wide-bandgap semiconductor with significant potential for detecting various types of radiation. An additional advantage is the commercial availability of high-quality crystalline SiC materials necessary for the fabrication of radiation detectors. The 4H-SiC polytype is a good candidate because of a band gap energy of 3.23 eV at room temperature, a breakdown voltage of approximately 2 MV/cm, and a carrier saturation velocity of 2×10e7 cm/s. Due to these properties, SiC detector is a high-temperature, radiation-tolerant alternative to traditional silicon detectors. Current epitaxial growth methods can produce SiC layers thicker than 100 μm; however, for full depletion, about 1kV of reverse bias is needed. We have studied the influence of different metallizations on the electrical and detection properties of 4H-SiC detectors based on a high-quality epitaxial layers.
We have fabricated 4H-SiC detector structures based on a 100 um thick epitaxial layer grown on 4” 4H-SiC substrates. For detector preparation, the base wafer was cut into smaller parts. On the top (epitaxial layer) part, Schottky contacts were prepared using different metallizations. We utilized three types of elements (nickel, aluminium, and silver). The contact thickness was 50 nm with diameters of 1 and 2 mm. On the opposite detector side (base substrate), the whole area metallization based on Ti/Pt/Au was deposited. Prepared detector structures were placed in the shielded box, and current-voltage measurements were performed. The highest breakdown voltage was achieved with the standard Ni contact, to be of about 600 V. The lowest observable breakdown showed the detector structures with Ag contacts, which was at 400 V, while the highest leakage current ( up to10 nA) flows in detectors with Al contacts. In the case of Ag and Ni contacts, the leakage current was almost the same, and the value was in the range of 20 pA up to 40 pA. Radiation detection properties were tested using a triple alpha radiation source 238-Pu, 239-Pu, 244-Cm, which generated alpha particles with energies in the range from 5.1 MeV up to 5.8 MeV. The best obtained energy resolution of about 20 keV in FWHM (Full Width at Half Maximum) was observable for detectors with Ni contact. Also, structures with Al contact demonstrate high energy resolution, close to 20 keV, despite the highest leakage current. The worst energy resolution was observable in the case of Ag contact, which was surprisingly having the low leakage current comparable to Ni structures.
Acknowledgement: This work was partially supported by grants of the Slovak Research and Development Agency Nos. APVV-22-0382, SK-CZ-RD-21-0116 and funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I05-03-V02-00073.