8 MeV Proton Irradiation Damage and Its Recovery by Annealing on Single-Crystalline Zinc Oxide Crystals
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8 MeV Proton Irradiation Damage and Its Recovery by Annealing on Single-Crystalline Zinc Oxide Crystals Kazuto Koike1, Ryugo Fujimoto1, Ryota Wada1, Shigehiko Sasa1, Mitsuaki Yano1, Shun-ichi Gonda2, Ryoya Ishigami3 and Kyo Kume3 1 Nanomaterials Microdevices Research Center, Osaka Institute of Technology, Ohmiya, Asahiku, Osaka 535-8585, Japan 2 The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka, Ibaraki-city, Osaka 567-0047, Japan 3 The Wakasa Wan Energy Research Center, Nagatani, Tsuruga-city, Fukui 914-0192, Japan. ABSTRACT II-VI compound semiconductor ZnO has a potential for high radiation hardness since large threshold displacement energy of constituent atoms can be expected due to the small unit-cell volume and large bandgap energy of 3.37 eV. In order to study the radiation hardness, singlecrystalline c-axis-oriented O-polar ZnO films with and without two-dimensional electron gas, a Zn-polar ZnO bulk crystal, and a Ga-polar GaN bulk crystal for comparison, were irradiated by an 8 MeV proton beam using a tandem-type accelerator. The radiation damage increased the electrical resistance and decreased the photoluminescence (PL) intensity of these samples with the increase of proton fluence over specific threshold values. In agreement with the expectation, ZnO samples were revealed to have superior radiation hardness; the threshold fluences for the deterioration of PL intensity were 3u1013 p/cm2 for the GaN bulk crystal, 2u1014 p/cm2 for the ZnO bulk crystal, and 5u1014 p/cm2 for the two ZnO films, in accordance with the order of the threshold fluences for the electrical resistance increase. The effect of post-irradiation annealing was also studied for these damaged bulk crystals; both electrical and optical properties of the ZnO bulk crystal were almost recovered to the pre-irradiation values, however, only the electrical properties of the GaN bulk crystal were recovered, by the annealing up to 700qC. Such a rapid recovery of the ZnO bulk crystal indicates the easy annihilation of Zn vacancy complexes acting as non-radiative centers by the recombination with interstitial Zn atoms. Since the migration barrier height energy of interstitial Zn atoms is known to be so small that it might occur even at room temperature, we ascribed the superior radiation hardness of ZnO crystals to the restoration of damage-induced defects by a self-annealing effect during irradiation. INTRODUCTION The space environment consists of many different types of the charged and uncharged particles in keV to MeV energy range [1-6]. The dominant particles are electrons, neutrons and protons. Exposure to these particles typically degrades the electrical and optical performance of semiconductor devices. The ability to predict how these devices respond in a particle radiation environment is of utmost importance in investigating the expected operating lifetime. Nonionizing energy loss (NIEL), usually defined in units of keVcm2/g, is a quantity that describes the rate of energy loss due to atomic displacements as a par
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