On the Electrical and Photoluminescence Properties of Erbium Doped ZnO Thin Film
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On the Electrical and Photoluminescence Properties of Erbium Doped ZnO Thin Film Liang-Chiun Chao, Chung-Chi Liau and Wan-Chun Chang Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan 106. ABSTRACT Er doped ZnO (Er:ZnO) thin films with Er concentration from 0.1 to 3.6 at. % were prepared by dual beam ion beam sputter deposition at room temperature. Experimental results show that as Er concentration increases from 0.1 to 1.1 at. %, the resistivity of the as-deposited Er:ZnO film decreases from 560 Ω⋅cm to a minimum of 0.23 Ω⋅cm, while further increasing Er concentration to 3.6 at. % results in increase of the resistivity to 4.2 kΩ⋅cm. The as-deposited Er:ZnO with Er concentration of 1.1 at.% also exhibits the highest carrier concentration of 2.3×1019 cm-3. None of the as-deposited Er:ZnO films show 1.5 μm emission without postgrowth annealing. Er:ZnO film with Er concentration at 0.5~1.1 at.% shows the strongest 1.5 μm emission after annealing at 700 ~ 900°C, while all the Er:ZnO film becomes semi-insulating after annealing. The discrepancy between the processing conditions for optimized carrier concentration and optimized optically activated Er ions may due to the formation of the pseudooctahedral structure after annealing that favors the 1.5 μm emission. INTRODUCTION Rare earth (RE) elements have attracted much attention due to their unique optical properties that RE elements have been widely doped in oxide and fluoride glasses1, 2. The characteristic 1.54 μm emission from Er that corresponds to minimum absorption in silica fiber is of particular interest. The incorporation of Er3+ into semiconductor materials, especially silicon3, has been intensively studied that the integration of opto-electronic integrated circuits may become a reality. However, Er doped silicon is plagued by low equilibrium solubility (~1×1018 cm-3) and thermal quenching effects that useful emission from erbium doped Si has not been achieved. The 1.54 μm emission of Er3+ in Si can be enhanced by co-doping of oxygen, while oxygen also causes the formation of silicon oxide that forms electrically insulating phases4. ZnO is a promising candidate for doping with rare earth elements due to its wide band gap (~ 3.37 eV at room temperature) and large exciton binding energy (60 meV). The wide band gap characteristic may reduce thermal quenching effect, while the large exciton binding energy may lead to efficient energy transfer from exciton to Er3+ ions. Er doped ZnO has been prepared by sol-gel5~7, laser ablation8, 9 and ion implantation10. Ion beam sputter (IBS) deposition is an essential technique in thin film deposition, and using it Er:ZnO can be grown by depositing alternative layers of Er and ZnO11. In this article, we report the electrical and photoluminescence (PL) properties of Er doped ZnO (Er:ZnO) prepared by reactive dual beam ion beam sputter deposition.
EXPERIMENT Er:ZnO thin films were deposited by reactive ion beam sputter deposition utilizing two capillary gas field ion source
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