Comparison of the effects of electrons and X-rays irradiation on epitaxial layers of 4H-SiC

Abstract

4H-SiC is one of the most promising indirect wide-bandgap (3.3 eV) semiconductor for high-power and high-temperature devices due to its high endurance and temperature resistance [1]. Furthermore, silicon carbide has high chemical stability and radiation hardness so 4H-SiC is ideal also to be employed in space applications and radiation harsh environments [2-4]. Consequently, in recent years the interest in the study of native SiC and the comparison with the effects of ionizing radiation has grown [5-7] aiming to evidence the features of the transport properties, the SiC structure and the presence of defects (extended or point defects). In view of applications, the study of epitaxial layers appositely grown is of large interest as well as their radiation sensitivity. In this work some complementary techniques (micro-Raman, absorption, steady-state and time resolved photoluminescence spectroscopy) have been used to study the properties of bulk and epitaxial layer of 4H-SiC and explore the effects of ionizing radiation on them by using electrons and X-rays. The dose range spanned from 1 kGy up to 105 kGy for electrons and 10 kGy for X-rays. Micro-Raman and absorption spectra enabled to evidence the presence of regions of different doping in the native samples. The epitaxial growth is instead of quite uniform doping. Stationary photoluminescence highlighted the presence of the defects associated emission (2.1-2.6 eV), probably due to the stacking faults. Time resolved spectroscopy was very useful to probe the quality of the epitaxial growth by monitoring the lifetime of the excitonic band. In particular, differences in lifetime have been highlighted suggesting the presence of recombination centers related to defects that induced shortening of the lifetime of the excitonic band. A comparison of lifetime of the excitonic band of epitaxial 4H-SiC irradiated with electrons (2.5 MeV) and X-rays (X-ray tube W target, operating at anode bias voltage 28 kV) has been considered to evaluate the presence of defects induced by the two different sources. The behavior of the material irradiated with electrons and X-rays is very different. In the samples irradiated with electron beam the lifetime of the excitonic band decreases when the deposited dose increases. Instead, in the samples irradiated with X-rays at similar doses there are not modification of the lifetime of the excitonic band. These findings suggest that irradiation with electrons induces defects related to atomic displacement [8]. Finally, the effects of thermal treatments in air have been explored to study the recovery of 4H-SiC properties. [1] T. Kimoto P. and J.A. Cooper, Fundamentals of Silicon Carbide Technology. John Wiley & Sons Singapore Pte. Ltd, 2014. [2] J. M. Rati et al., IEEE Transactions on Nuclear Science, vol. 67, no. 12, 2020. [3] F. Nava, G. Bertuccio, A. Cavallini and E. Vittone, Measurement Science and Technology, vol. 19, no.10, 2008. [4] A. A. Lebedev, V. V. Kozlovski, K. S. Davydovskaya, and M. E. Levinshtein, G. Bertuccio, Materials, vol. 14, no.17, 2021. [5] A. A. Lebedev, V. V. Kozlovski, N. B. Strokan, D. V. Davvdov, A. M. Ivanov, A. M. Strel’chuck et al. Materials Science Forum, Vol. 433-436, 2003. [6] A. Le Donne, S. Binetti, S. Pizzini. Diamond & Related Materials, vol. 14, 2005. [7] I. P. Vali, P. K. Shettya, M.G. Mahesha, V.G. Sathe, D.M. Phase, R.J. Choudhary. Nuclear Inst. And Methods in Physics Research B, vol. 440, 2019. [8] P. Hazdra, J. Vobecký. Phys. Status Solidi A, vol. 216, 2019.