Structure and properties of ion-beam-modified (6H) silicon carbide

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Abstract

The ion-beam-induced crystalline-to-amorphous phase transition in single crystal (6H) α-SiC has been studied as a function of irradiation temperature. The evolution of the amorphous state has been followed in situ by transmission electron microscopy in specimens irradiated with 0.8 MeV Ne+, 1.0 MeV Ar+, and 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K. The threshold displacement dose for complete amorphization in α-SiC at 20 K is 0.30 dpa (damage energy=15 eV atom−1). The dose for complete amorphization increases with temperature due to simultaneous recovery processes that can be adequately modeled in terms of a single-activated process. The critical temperature, above which amorphization does not occur, increases with particle mass and saturates at about 500 K. Single crystals of α-SiC with [0001] orientation have also been irradiated at 300 K with 360 keV Ar2+ ions at an incident angle of 25° over fluences ranging from 1 to 8 Ar2+ ions nm−2. The damage accumulation in these samples has been characterized ex situ by Rutherford backscattering spectrometry–channeling (RBS/C) along the [0001] direction, Raman spectroscopy, cross-sectional transmission electron microscopy (XTEM), and mechanical microprobe measurements.

Introduction

The high-temperature semiconducting properties and high thermal conductivity of silicon carbide (SiC) make it a promising material for high-temperature, high-power, and high-speed electronic devices. Silicon carbide is also a candidate material for structural components in fusion reactor systems and is proposed as an inert host matrix for the burn-up of excess weapons plutonium using nuclear reactors or accelerator-based neutron sources. A fundamental understanding of irradiation effects in SiC is required to effectively utilize ion-implantation techniques in electronic device fabrication and to predict performance in nuclear environments.

Hexagonal α-SiC (6H polytype) is one of the SiC polymorphs of interest for these applications, and many investigators have studied ion-beam-induced defect accumulation and amorphization in α-SiC at room temperature 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Defect annealing in ion-irradiated α-SiC 15, 16and the temperature dependence of defect accumulation and amorphization in α-SiC under ion-beam 17, 18, 19, 20, 21and electron-beam 22, 23, 24irradiation have also been investigated. In general, the damage accumulation in α-SiC irradiated at different temperatures has been studied using ex situ characterization techniques, such as Rutherford backscattering spectrometry in channeling geometry (RBS/C) 2, 6, 17, 18and cross-sectional transmission electron microscopy (XTEM) 9, 18, 20, 21. Recently, the authors have used in situ electron microscopy 19, 25and in situ RBS/C techniques 19, 26, 27, 28to characterize damage accumulation as a function of temperature in both α-SiC and β-SiC. In the present paper, the results of a detailed in situ investigation on the effects of different ion species on damage accumulation and amorphization in α-SiC are reported, along with the results of ex situ RBS/C, Raman spectroscopy, XTEM, and mechanical microprobe measurements as a function of accumulated dose.

Section snippets

Experimental procedures

The n-type α-SiC (6H polytype) single crystal wafers used in this study were obtained from Cree Research, and were oriented on the [0001] axis. For the in situ irradiation studies at the HVEM-Tandem Facility at Argonne National Laboratory [29], 3 mm diameter specimens were ultrasonically cut from thinned sections and then prepared as TEM specimens by Ar+ ion milling. The irradiation studies were performed at ∼5° off the [0001] axis with 0.8 MeV Ne+, 1.0 MeV Ar+, and 1.5 MeV Xe+ ions at a flux

TEM of amorphization process

The irradiation-induced amorphization of α-SiC has been well documented 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28; however, the nature of this crystalline-to-amorphous transformation is still not well understood. In situ electron diffraction is used to qualitatively follow the progression of the amorphization process under irradiation at the HVEM-Tandem facility, as illustrated previously for β-SiC [25]. In general, a single crystal

Conclusions

The temperature dependence of the ion-beam-induced crystalline-to-amorphous phase transition in α-SiC has been determined in situ by transmission electron microscopy in specimens irradiated with 0.8 MeV Ne+, 1.0 MeV Ar+, and 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K. The threshold displacement dose for complete amorphization in α-SiC at 20 K is 0.30 dpa (damage energy=15 eV atom−1). The dose for complete amorphization increases with temperature due to simultaneous recovery

Acknowledgements

The authors thank the HVEM-Tandem Facility staff at Argonne National Laboratory and J.R. Tesmer, M. Nastasi, K.E. Sickafus and the staff of the Ion Beam Materials Laboratory at Los Alamos National Laboratory for their assistance with the irradiation experiments. The authors also thank Y. Guo of the University of New Mexico for assistance with the preparation of XTEM samples. This research was supported by the Division of Materials Sciences, Office of Basic Energy Sciences, US Department of

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