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Description
Silicon carbide (SiC) is a promising semiconductor material for the fabrication of radiation detectors, largely due to its advantageous characteristics, including high chemical and temperature stability, as well as radiation hardness. Silicon carbide (SiC) is capable of crystallising in several different modifications, including 3C, 4H and 6H polytypes. The most favourable for the fabrication of radiation detectors is 4H-SiC polytype. The detectors based on 4H-SiC are capable of functioning not only at room temperature but also at elevated temperatures, due to the wide bandgap, high mobility of charge carriers, and high saturation velocity. Furthermore, the material is commercially available, which represents a significant benefit. A major advantage of SiC-based radiation detectors is also their ability to directly register neutrons, as they contain light carbon atoms compared to silicon-based detectors.
Two types of 4H-SiC semiconductor detectors for ionizing radiation can be distinguished on the basis of their way to block the thermally and by defects generated current flowing through the structure. One group is based on PN junctions, while the other is based on Schottky contacts. The objective of this study is to compare these two types of 4H-SiC radiation detectors. Additionally, the study will examine the impact of varying thicknesses of the n-layer or epitaxial layer of 4H-SiC material on the quality of the fabricated detectors in terms of electrical characteristics measurements.
Two sets of 4H-SiC detectors were prepared. The first set of detectors is based on PN junction and was prepared from 350 µm substrate with three different n-layer thicknesses of 20, 60 and 100 µm and contact diameter of 1.5 mm. The set of detectors with Schottky contacts was also made from 350 µm 4H-SiC substrate and four different epitaxial layer thicknesses of 25, 50, 80 and 100 µm with a Schottky contact diameter of 2 mm. The results indicate that the Schottky type detectors exhibit a predisposition for better detection and spectrometric properties, particularly in regard to the reverse current, which represents the background noise to the signal from the registered radiation, as well as the breakdown voltage, which limits the operating voltage. The reverse current density for 4H-SiC detectors with Schottky contacts is approximately 10e-11 A/mm^2, while results in the range of 10e-9 to 10e-8 A/mm^2 have been obtained for PN junction detector samples. The thickness of the epitaxial layer also affects the electrical properties of the detectors, with superior results being obtained when the epitaxial layer is thinner.
The authors acknowledge funding from the Slovak Research and Development Agency (Research Projects APVV-22-0382 and APVV-18-0243).
