Nature of Tunable Optical Reflectivity of Rocksalt Hafnium Nitride Films

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• 作者：Chaoquan Hu ; Zhiqing Gu ; Jianbo Wang ; Kan Zhang ; Xiaobo Zhang ; Mingming Li ; Sam Zhang ; Xiaofeng Fan ; Weitao Zheng
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：September 4, 2014
• 年：2014
• 卷：118
• 期：35
• 页码：20511-20520
• 全文大小：689K
• ISSN：1932-7455

文摘

Although the phenomenon that optical reflectivity of hard group IVB transition metal nitrides depends on stoichiometry has been reported, the microscopic origin of this behavior has not been well explored yet. Here we find that optical reflectivity of rocksalt hafnium nitride films (未-HfN_x) can be effectively tuned by stoichiometry x, and the underlying mechanism can be well elucidated by Drude鈥揕orentz fitting and first-principles calculations. It is shown that the observed tunability of optical reflectivity arises from a transition from N vacancies (V_N) to Hf vacancies (V_Hf) in the films because this evolution from V_N to V_Hf has important roles in changing electronic properties of the films in the following three aspects: (i) density of free electrons, wherein V_N and V_Hf act as donor-like and acceptor-like defects, respectively; (ii) mean free path of free electrons, in which V_N and V_Hf are the main electron scattering sites in sub- and overstoichiometric films, respectively; (iii) interband transition absorption of bound electrons, wherein three previously unreported absorption bands originating from V_N and V_Hf are found to occur at 鈭?.81, 2.27, and 3.75 eV. These point-defect-induced variations significantly affect the dielectric function of 未-HfN_x films and thus drive the tailored evolution in reflectivity properties with x.