Influence of Neutron Transmutation Doping on Optical Properties of Ge Nanocrystals Prepared by Ion implantation
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Influence of Neutron Transmutation Doping on Optical Properties of Ge Nanocrystals Prepared by Ion implantation Shaobo Dun, Tiecheng Lu1, Qiang Hu, Ningkang Huang Department of Physics and Key Laboratory for Radiation Physics & Technology of Ministry of Education, Sichuan University, Chengdu 610064, P. R. China 1 International Center for Material Physics, Chinese Academy of Sciences, Shenyang 110015, P. R. China Songbao Zhang, Bin Tang, Junlong Dai Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, P. R. China Lev Resnick, Issai Shlimak Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel Sha Zhu, Qiangmin Wei, Lumin Wang Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109, USA ABSTRACT Ge nanocrystals embedded in an amorphous SiO2 film on Si matrix were prepared by ion implantation and subsequent annealing. Neutron transmutation doping (NTD) technique was used to dope Ge nanocrystals with As impurities. The microstructure, phase and photoluminescence of NTDed Ge nanocrystals were analyzed and compared with undoped Ge nanocrystals. A new photoluminescence peak related to As impurities was found. It is discovered that impurities are expelled from larger clusters resulted from Ge nanocrystals aggregation on the sample surface. To prevent nanocrystal aggregation and assure uniform doping of As, it is necessary to adopt appropriate implantation and annealing conditions. INTRODUCTION Doping, the intentional introduction of impurities into a material, is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals [1-5]. Doping has been used for control the electrical and optical characters of nanocrystals by different doping methods, to fabricate novel photoelectrical devices [6-8]. Similarly, nanocrystalline Si (nc-Si) can be doped by chemical method, it is reported that quite strong 1540 nm photoluminescence (PL) emits from Er3+ doped Si nanostructures [9]. Ion implantation is another doping technique, which has been used for preparation of doped nc-Si, it is observed too that strong 1540 nm PL emits from Er3+ doped nc-Si [10], and the intensity of PL first increases then decreases with increasing doped P concentration [11]. The luminescence of doped nc-Ge is an interesting problem, but it has not been reported. The method of neutron transmutation doping (NTD) of semiconductors is based on nuclear transformation of materials following by their capture of thermal neutrons. NTD is achieved by
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irradiating materials with a neutron flux in a nuclear reactor and subsequent annealing process. The interest in NTD stems from two of its main advantages over the conventional chemical methods of impurity incorporation. First, this is high-precision doping, because the concentration of impurities introduced at a constant neutron flux is proportional to irradiation time, which can be controlled highly accuratel
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