Effects of beta ray irradiation on 4H-SiC epitaxial layer probed by exciton recombination

Abstract

Silicon Carbide (SiC) is a wide-bandgap crystalline semiconductor with an indirect bandgap of 2.3-3.3 eV depending on polytype. 4H-SiC is a very promising semiconductor for high-power devices and high-temperature devices thanks to its superior physical and electrical properties: it exhibits 10 times higher breakdown electric field strength and 3 times higher thermal conductivity than silicon, high chemical inertness, high thermal conductivity, high mechanical strength, high saturation drift velocity [1]. Furthermore, silicon carbide has high radiation hardness thanks to the large values of the threshold energy for defects formation. Consequently, SiC is the most promising semiconductor for fabrication of devices which can operate in extreme conditions, as high levels of irradiation, elevated temperatures, and high chemical activity [2]. Nonetheless, the characteristics of SiC-based devices are influenced by the presence of impurities as well as extended and point defects. In general, the effects of irradiation causes formation of vacancies, interstitials, and related defects which may give rise to states in the bandgap influencing the electrical and optical properties of the material [3-5]. In this work some complementary non-invasive techniques have been used to study the properties of epitaxial layer of 4H-SiC and to explore the effects of ionizing radiation on it by using β-rays and two different X-rays sources. The dose range spanned from 1 kGy up to 100 kGy. In the samples irradiated with electron beam the lifetime of the excitonic band decreases when the deposited dose increases. In particular, in the samples with higher native defectiveness the effect starts from lower deposited doses. Conversely, in the samples irradiated with X-rays there aren’t effects at the same deposited dose as β-rays. These findings suggest that irradiation with electrons induces defects related to atomic displacement. Finally, the effects of thermal treatments in air, from 100°C up to 900°C, have been explored to study the recovery properties of 4H-SiC.