Characterization of defects in n-type 4H-SiC after high-energy N ion implantation by RBS-channeling and Raman spectroscopy

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Abstract

Implantation with 1 MeV N ions was performed at room temperature in n-type 4H-SiC (0 0 0 1) at four implantation fluences (or doses in dpa (displacements per atom) at the damage peak) of 1.5 × 1013 (0.0034), 7.8 × 1013 (0.018), 1.5 × 1014 (0.034), and 7.8 × 1014 (0.178) ions/cm2, respectively. The evolution of disorder was studied using Rutherford backscattering spectrometry in channeling mode (RBS-C), Raman spectroscopy, and optical transmission. The disorder in the Si sub-lattice was found to be less than 10% for the dpa of 0.0034 and 0.0178 and increased to 40% and 60% for the dpa of 0.034 and 0.178 respectively. The normalized Raman intensity In, shows disorder of 41%, 69%, 77% and 100% for the dpa of 0.0034, 0.0178, 0.034 and 0.178, respectively. In this paper, the characterization of the defects produced due to the nitrogen implantation in 4H-SiC are presented and the results are discussed.

Introduction

The exceptional properties of SiC, including chemical inertness and small capture cross-sections for neutrons make it an outstanding candidate for devices in extreme environments such as in nuclear fusion reactors or cladding material for gas-cooled fission reactors and space applications [1]. Out of the three commonly available polytypes of SiC, 4H-SiC is considered to be the most advantageous. This polytype can be potentially used not only in high temperature environments [2] but also in high power and high frequency devices because of its superior electronic properties [3]. Weber et al. have investigated the defects in 4H-SiC using first principle calculations [4]. The results show that the isolated Si vacancies may possess properties similar to those of nitrogen-vacancy (N-V) centers, which can be potentially used to construct individual qubit states. Recently Rhim et al. have proposed that the nitrogen vacancy complexes exhibit magnetism in nitrogen doping of epitaxial graphene on SiC [5]. Hence, there is a necessity to study these defects, which are created during the irradiation as the improved understanding may lead to applications of these materials in nuclear environment and spintronics devices.

Capelletti et al. have investigated the phase formation in amorphous SiC thin films with 100 keV N+ ions by thermal annealing [6]. Gimbert et al. have studied the physical, chemical and electrical properties of nitrogen implanted p-type 4H- and 6H-SiC [7]. Zolnai et al. have explored the crystallographic orientation and influence of the ion fluence on the shape of damage distributions in n-type 6H-SiC implanted with 500 keV N+ ions [8]. Moscatelli et al. have investigated the electrical properties of N implanted p-type 4H-SiC [9]. Zhou et al. studied the mechanical properties of nitrogen implanted SiC [10]. All these studies were focused on N implantation in SiC polytypes but none of them studied the implantation induced disorder predominantly in n-type 4H-SiC at higher implantation energies. In this paper we report on the disorder produced by nitrogen ion implantation at an energy of 1 MeV in n-type 4H-SiC. The results obtained by the ion beam analysis techniques of RBS-C, Monte Carlo simulations using SRIM/TRIM-2012, Raman spectroscopy, and optical transmission are discussed.

Section snippets

Experiment

Single crystalline n-type 4H-SiC with (0 0 0 1) orientation (CREE Research, Inc.) was used in this research work. The samples were implanted with 1 MeV N ions using the 2.5 MV Van de Graaff accelerator (HVEC Type AK) at the Ion Beam Modification and Analysis Laboratory (IBMAL) of the University of North Texas. Four different fluences of 1.5 × 1013 ions/cm2, 7.8 × 1013 ions/cm2, 1.5 × 1014 ions/cm2 and 7.8 × 1014 ions/cm2 were implanted on four different pieces of SiC of sizes 10 mm × 5 mm. From SRIM/TRIM-2012

RBS-C

The RBS-C technique is a powerful technique to determine the disorder accumulation and the depth distribution of disorder in the implanted samples. In Fig. 1, the aligned RBS-C spectra of all implanted samples with different fluences are shown, together with the aligned and random spectra of the unimplanted sample. Fig. 1 clearly shows that as the implanted fluence increases, the backscattering yields from the respective samples in the aligned mode increases as well. Energy to depth conversions

Summary

N ions were implanted in n-type 4H-SiC at room temperature with the energy of 1 MeV using the Van de Graaff accelerator at IBMAL. The fluences implanted are 1.5 × 1013, 7.8 × 1013, 1.5 × 1014 and 7.8 × 1014 ions/cm2, which correspond to the dpa values of 0.0034, 0.0178, 0.034 and 0.178 at the damage peak, respectively. The experimentally determined depths of the Si damage peaks are 1050 ± 50 nm, whereas from SRIM/TRIM-2012 simulations, the simulated depth is 962 ± 44 nm. For the highest implanted fluence, a

Acknowledgements

The authors would like to thank the CART facility at UNT for Raman spectroscopy measurements. RBS-C experiment was performed at EMSL, a National Scientific User Facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Venkata C. Kummari was supported in part by the National Science Foundation Grant # 0960222.

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