3) The University of Electro-Communications, Tokyo, 182-8585, Japan Modul 10 γ - Ray Irradiation Effects on the Characteristics of New Material P Type 6H-SiC Ni-Schottky Diodes (Application For Nuclear Fuel Facilities) U. Sudjadi１), T. Ohshima２), N. Iwamoto２, ３), S. Hishiki２), and K. Kawano３) 1) Center For Nuclear Fuel Technology, BATAN ２) Japan Atomic Energy Agency (JAEA), Gunma 370-1292, Japan 3) The University of Electro-Communications, Tokyo, 182-8585, Japan Keywords: Current Density, On Resistance, Barrier Height, 6H SiC, Schottky Diodes, γ-ray Irradiation. Abstract. Effects of γ-ray irradiation on electrical characteristics of new material p type 6H-SiC Ni-Schottky diodes were investigated. Ni Schottky diodes fabricated on p type 6H-SiC epi-layer were irradiated with γ-rays at RT. The electrical characteristics of the diodes were evaluated before and after irradiation. The value of the on-resistance does not change up to 1 MGy, and the value increases with increasing absorbed dose above 1MGy. For n factor, no significant increase is observed below 500 kGy, however, the value increases above 500 kGy. Schottky Barrier Height (SBH) decreases with increasing absorbed dose. Leakage current tends to increase due to irradiation. Abstrak. Efek dari radiasi ɤ pada karakteristik kelistrikan dari Ni-diode Schottky material baru 6H-SiC tipe p telah diteliti. Ni-diode Schottky difabrikasi pada epi- layer 6H-SiC tipe p, di iradiasi dengan sinar ɤ pada temperatur ruang. Karakteristik kelistrikan dari diode telah dievaluasi sebelum dan setelah iradiasi. Harga dari on resistance tidak berubah sampai 1 MGy, dan harganya mengalami kenaikan dengan naiknya penyerapan dosis diatas 1MGy. Untuk n-factor, diamati dibawah 500 kGy kenaikannya tidak significant, tetapi diamati diatas 500 kGy harganya naik. Schottky Barrier Height (SBH) turun dengan kenaikan dosis penyerapan. Disebabkan oleh iradiasi, kebocoran arus kecenderungannya naik. Introduction. Silicon carbide (SiC) material is a promising candidate for high power and high frequency electronic devices because of its excellent thermal and electrical properties such as stability at high temperature, wide band gap, high breakdown field, and high thermal conductivity. In addition, since SiC has a strong radiation resistance, it is also expected to be widely applied in electronic devices used in harsh radiation environments such as nuclear power plants, nuclear fuel facilities, accelerator facilities, space and so on [1,2]. For the development of radiation hard devices based on SiC, it is very important to study radiation response of devices. Gamma-ray irradiation effect on the characteristics of SiC Schottky diodes have been studied by a few researchers. M. Bruzzi et al. have irradiated n-type 4H-SiC Schottky diodes with γ-ray in the dose range 0.1 – 1 Gy. M. Bruzzi et al. have also applied 4H-SiC material for radiation dosimetry [3, 4]. Nava et al. have investigated the radiation tolerance of epitaxial n-type 4H-SiC detector for electrons and γ-rays. Nava et al. have irradiated http://www.mercubuana.ac.id 1

Where A. = (m. /m0), m. is effective hole mass, and A Where A*= (m*/m0), m* is effective hole mass, and A* is effective Richardson constant. In this analysis, we employ for 6H-SiC m*= 0.71 m0, and A* for 6H-SiC is 194.1 (A/cm2)/K2. Figure 3 shows on resistance dependence of the absorbed dose of p-type SiC Schottky diode samples with 150 μm and 300 μm circular diameters. The value of the on-resistance does not change up to 1 MGy, and the value increases with increasing absorbed dose above 1 MGy. Figure 4 shows n-factor (ideality factor) dependence of the absorbed dose of p-type SiC Schottky diode samples with 150 μm and 300 μm circular diameters. The n-factor is no significant increases below 500 kGy, however n-factor increases above 500 kGy. According data in Figures 3 and 4 that on resistance and n-factor does not change up to 1 MGy and 500 kGy, it is clear that the new material 6H-SiC has a strong radiation resistance。 It is also clear that the new material 6H-SiC expected to be widely applied in electronic devices and detector used in harsh radiation environments such as nuclear power plants, nuclear fuel facilities, accelerator facilities, space and so on. If comparing with Si as material base for electronic devices. Si material has a low radiation resistance. Si material has a short life time and not function well for electronic devices and detector in high radiation area such as nuclear fuel facilities, nuclear power plants, accelerator facilities, aerospace etc. [8]. Figure 5 shows Schottky barrier height (SBH) dependence of the absorbed dose of p- type SiC Schottky diode samples with 150 μm and 300 μm circular diameters. The SBH decreases with increasing absorbed dose. Figure 6 shows current density versus reverse bias of p-type SiC Schottky diode sample with 250 μm circular diameter. As shown in this figure, the leakage current tends to increase due to gamma-ray irradiation. 10 Ni,=250m Ni,=250m 1 8 2 2 6 10 -3 Current Density (A/cm ) 4 2 0MR 3MR 10MR 69MR Current Density (A/cm ) 0MR 3MR 10MR 69MR 10 -6 0.0 10 0.0 -9 0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 Forward Bias (V) Forward Bias (V) Fig. 1 Current density versus forward bias Fig. 2 Semi-logarithmic plot of current density (J) versus forward bias (V) http://www.mercubuana.ac.id 3

increase due to irradiation. In the case of C2 = 0, where the density of interface state is ∞ the Fermi level at the interface is pinned by the surface state at the value Φ0 (neutral level, which is the position that the Fermi level must assume if the surface is electrically neutral) above the valence band. The SBH is independent of the metal work function. This situation of the strongest pinning is the Bardeen limit. When C2 is 1, the situation is called the Schottky limit, where the density of interface is zero. It means Fermi level is free from pinning. In the samples, we suggest after irradiated with gamma ray, the SBH decreases with increasing absorbed dose, where the value of proportional factor C2 increases with increasing absorbed dose, and the density of interface state decreases with increasing absorbed dose. Therefore SBH decreases with increasing absorbed dose (see Fig. 5). The increase ideality factor above 500 kGy is indicating an increase of defect density at the interface with increasing gamma ray irradiation dose and/or the increase of the ideality factor is due to the lateral in-homogeneity of barrier height (see Fig. 4) [12]. The ideality factor no significant increase is observed below 500 kGy, this result is not normal behavior, a possible probability this fact is due to un-sensitivity, of the mean barrier height variation to the field and/or un-sensitivity the barrier height standard deviation, variation to the field. The electrical properties change of Schottky diodes after gamma irradiation, are strongly depend on of the fabrication process and the absorbed dose of gamma ray irradiation. Irradiation of gamma-ray to the Schottky diodes created Compton and photoelectric effects. Electrons produced from the Compton and photoelectric effects are the dominant contributions to the electron flux generated in a metal semiconductor interface of the p-type 6H-SiC Schottky diode of the samples. Co60 source in cascade have energies of 1,173 and 1.332 MeV, respectively. They are customarily approximated by a single energy 1.25 MeV [13, 14]. Photons of this energy produce Compton electrons which provide a main contribution to primary production in metal (Nickel), semiconductor (6HSiC), and metal semiconductor (Nickel and 6HSiC) interface. These electrons have influenced to the electrical properties change of the p-type 6H-SiC Schottky diodes of the samples. Summary Ni Schottky diodes fabricated on p-type 6H-SiC epi-layer were irradiated with gamma-rays, and the electrical characteristics of the diodes were evaluated. The value of the on-resistance does not change up to 1 MGy, and the value increases with increasing absorbed dose above 1 MGy. For n factor, no significant increase is observed below 500 kGy, however, the value increases above 500 kGy. Schottky barrier height decreases with increasing absorbed dose. Leakage current tends to increase due to irradiation. http://www.mercubuana.ac.id 5