Ag-Cr共掺LiZnP新型稀磁半导体的光电性质
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摘要
采用基于密度泛函理论的第一性原理平面波超软赝势法,对纯Li Zn P, Ag/Cr单掺和Ag-Cr共掺Li Zn P新型稀磁半导体进行了结构优化,计算并分析了掺杂体系的电子结构、磁性、形成能、差分电荷密度和光学性质.结果表明:非磁性元素Ag单掺后,材料表现为金属顺磁性;磁性元素Cr单掺后, sp-d杂化使态密度峰出现劈裂,体系变成金属铁磁性;而Ag-Cr共掺后,其性质与Ag和Cr单掺完全不同,变为半金属铁磁性,带隙值略微减小,导电能力增强,同时形成能降低,原子间的相互作用和键强度增强,晶胞的稳定性增强.通过比较光学性质发现,掺杂体系的介电函数虚部和光吸收谱在低能区均出现新的峰值,且当Ag-Cr共掺时介电峰峰值最高,同时复折射率函数在低能区发生明显变化,吸收边向低能方向延展,体系对低频电磁波吸收加强.
Spintronic devices utilize the electron charge and spin degree of freedom to achieve novel quantum functionalities.Diluted magnetic semiconductors(DMS) constitute an important category of spintronic materials that have the potential to be successfully incorporated into the existing semiconductor industry. The prototypical DMS(Ga,Mn)As, discovered in the 1990 s, accomplishes spin and charge doping simultaneously through the heterovalent substitution of the magnetic ion Mn~(2+) for Ga~(3+). Two challenges have presented themselves in this material. First, the heterovalent nature of this "integrated spin/charge" doping results in severely limited chemical solubility in(Ga,Mn)As, restricting specimen fabrication to metastable thin films by molecular beam epitaxy; second, the simultaneous spin and charge doping precludes the possibility of individually tuning the spin and charge degree of freedom. A new type of ferromagnetic DMS based on I-II-V group can overcome both of these challenges. Li(Zn,Mn)As utilizes excess Li concentration to introduce hole carriers, while independently making the isovalent substitution of Mn~(2+) for Zn~(2+) in order to achieve local spin doping. With no heterovalent substitution to restrict chemical solubility, bulk samples of Li(Zn,Mn)As are successfully fabricated. However, one drawback of Li(Zn,Mn)As is its use of the toxic element As. The isostructural direct-gap semiconductor LiZnP also undergoes a ferromagnetic transition upon Mn doping, and its bulk magnetic properties are very similar to those of Li Zn As.In this paper, the geometric structure of pure LiZnP, Ag doped, Cr doped, and Ag-Cr co-doped LiZnP new diluted magnetic semiconductor are optimized by using the first-principles plane wave ultra-soft pseudo-potential technology based on the density function theory. Then we calculate the electronic structure, magnetism, formation energy, differential charge density, and optical properties of the doped systems. The results show that the material is a paramagnetic metal after single doping of the nonmagnetic element Ag. When magnetic element Cr is doped with LiZnP, sp-d orbital hybridization makes the peak of density of state nearly EF-split, leading the system to become metallic ferromagnetism.However, Ag-Cr co-doped LiZnP changes into half-metallic ferromagnetism, which is completely different from the single doping system. The band gap decreases slightly, and the electrical conductivity is enhanced. Meanwhile, the formation energy of the system becomes lower, the bond between atoms strengthens, and the stability of the unit cell becomes stronger. A comparison of the optical properties indicate that the imaginary part of dielectric function and the optical absorption spectrum both present new peaks in low energy region in the doped systems. Ag-Cr co-doped LiZnP has the highest dielectric peak. Meanwhile, the complex refractive index function changes obviously in a low energy region,and the absorption edge extends to the low energy direction. The system enhances the absorption of low-frequency electromagnetic waves.
Spintronic devices utilize the electron charge and spin degree of freedom to achieve novel quantum functionalities.Diluted magnetic semiconductors(DMS) constitute an important category of spintronic materials that have the potential to be successfully incorporated into the existing semiconductor industry. The prototypical DMS(Ga,Mn)As, discovered in the 1990 s, accomplishes spin and charge doping simultaneously through the heterovalent substitution of the magnetic ion Mn~(2+) for Ga~(3+). Two challenges have presented themselves in this material. First, the heterovalent nature of this "integrated spin/charge" doping results in severely limited chemical solubility in(Ga,Mn)As, restricting specimen fabrication to metastable thin films by molecular beam epitaxy; second, the simultaneous spin and charge doping precludes the possibility of individually tuning the spin and charge degree of freedom. A new type of ferromagnetic DMS based on I-II-V group can overcome both of these challenges. Li(Zn,Mn)As utilizes excess Li concentration to introduce hole carriers, while independently making the isovalent substitution of Mn~(2+) for Zn~(2+) in order to achieve local spin doping. With no heterovalent substitution to restrict chemical solubility, bulk samples of Li(Zn,Mn)As are successfully fabricated. However, one drawback of Li(Zn,Mn)As is its use of the toxic element As. The isostructural direct-gap semiconductor LiZnP also undergoes a ferromagnetic transition upon Mn doping, and its bulk magnetic properties are very similar to those of Li Zn As.In this paper, the geometric structure of pure LiZnP, Ag doped, Cr doped, and Ag-Cr co-doped LiZnP new diluted magnetic semiconductor are optimized by using the first-principles plane wave ultra-soft pseudo-potential technology based on the density function theory. Then we calculate the electronic structure, magnetism, formation energy, differential charge density, and optical properties of the doped systems. The results show that the material is a paramagnetic metal after single doping of the nonmagnetic element Ag. When magnetic element Cr is doped with LiZnP, sp-d orbital hybridization makes the peak of density of state nearly EF-split, leading the system to become metallic ferromagnetism.However, Ag-Cr co-doped LiZnP changes into half-metallic ferromagnetism, which is completely different from the single doping system. The band gap decreases slightly, and the electrical conductivity is enhanced. Meanwhile, the formation energy of the system becomes lower, the bond between atoms strengthens, and the stability of the unit cell becomes stronger. A comparison of the optical properties indicate that the imaginary part of dielectric function and the optical absorption spectrum both present new peaks in low energy region in the doped systems. Ag-Cr co-doped LiZnP has the highest dielectric peak. Meanwhile, the complex refractive index function changes obviously in a low energy region,and the absorption edge extends to the low energy direction. The system enhances the absorption of low-frequency electromagnetic waves.
引文
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[2]Wang Y,Zhan Y Z,Xu Y F,Yu Z W 2007 Mate.Rev.21 20(in Chinese)[王颖,湛永钟,许艳飞,喻正文2007材料导报21 20]
[3]Deng Z,Zhao K,Jin C Q 2013 Physics 10 682(in Chinese)[邓正,赵侃,靳常青2013物理10 682]
[4]Ma?ek J,KudrnovskyJ,Máca F,Gallagher B L,Campion R P,Gregory D H,Jungwirth T 2007 Phys.Rev.Lett.98 067202
[5]Deng Z,Jin C Q,Liu Q Q,Wang X C,Zhu J L,Feng SM,Chen L C 2011 Nat.Commun.2 422
[6]Wang A L,Wu Z M,Wang C,Hu A Y,Zhao R Y 2013Acta Phys.Sin.62 137101(in Chinese)[王爱玲,毋志民,王聪,胡爱元,赵若禺2013物理学报62 137101]
[7]Qin C 2013 M.S.Thesis(Hangzhou:Zhejiang University)(in Chinese)[秦川2013硕士学位论文(杭州:浙江大学)]
[8]Jairo Sinova J,Ma?ek J,Ku?era J,Mac Donald A H 2006Rev.Mod.Phys.78 809
[9]Ding C,Man H Y,Qin C,Lu J C,Sun Y L,Wang Q,Yu B Q,Feng C M,Goko T,Arguello C J,Liu L,Frandsen B A,Uemura Y J,Wang H D,Luetkens H,Morenzoni E,Han W,Jin C Q,Munsie T,Williams T J,D’Ortenzio RM,Medina T,Luke G M,Imai T,Ning F L 2013 Phys.Rev.B 88 041102
[10]Guan Y Q,Chen Y,Zhao C W 2010 Mat.Sci.Eng.Pow.Met.15 521(in Chinese)[关玉琴,陈余,赵春旺2010粉末冶金材料科学与工程15 521]
[11]Cui X Y,Medvedeva J E,Delley B,Freeman A J,Newman N,Stampfl C 2005 Phys.Rev.Lett.95 256404
[12]Lin Z,Guo Z Y,Bi Y J,Dong Y C 2009 Acta Phys.Sin.58 1917(in Chinese)[林竹,郭志友,毕艳军,董玉成2009物理学报58 1917]
[13]Wu Z H,Xie H Q,Zen Q F 2013 Acta Phys.Sin.62097301(in Chinese)[吴子华,谢华清,曾庆峰2013物理学报62 097301]
[14]Deng J Q,Wu Z M,Wang A L,Hu A Y,Zhao R Y 2014Comp.Phys.31 617(in Chinese)[邓军权,毋志民,王爱玲,胡爱元,赵若禺2014计算物理31 617]
[15]Chen B J,Deng Z,Li W M,Gao M,Zhao J F,Zhao GQ,Yu S,Wang X C,Liu Q Q,Jin C Q 2016 Aip.Adv.6 115014
[16]Wei S H,Zunger A 1986 Phys.Rev.Lett.56 528
[17]Kuriyama K,Nakamura F 1987 Phys.Rev.B 36 4439
[18]Segall M D,Lindan P J D,Probert M J,Pickard C J,Hasnip P J,Clark S J,Payne M C 2002 Phys.Cond.Mat.14 2717
[19]Vanderbilt D 1990 Phys.Rev.B 41 7892
[20]Monkhorst H J,Pack J D 1976 Phys.Rev.B 13 5188
[21]Chen K,Fan G H,Zhang Y,Ding S F 2008 Acta Phys.Sin.57 3138(in Chinese)[陈琨,范广涵,章勇,丁少锋2008物理学报57 3138]
[22]Guan L,Li Q,Zhao Q S,Guo J X,Zhou Y,Jin L T,Geng B,Liu B T 2009 Acta Phys.Sin.58 5624(in Chinese)[关丽,李强,赵庆勋,郭建新,周阳,金利涛,耿波,刘保亭2009物理学报58 5624]
[23]Wen P,Li C F,Zhao Y,Zhang F C,Tong L H 2014 Acta Phys.Sin.63 197101(in Chinese)[文平,李春福,赵毅,张凤春,童丽华2014物理学报63 197101]
[24]Ru Q,Li Y L,Hu S J,Peng W,Zhang Z W 2012 Acta Phys.Sin.61 038210(in Chinese)[汝强,李燕玲,胡社军,彭薇,张志文2012物理学报61 038210]
[25]Duan M Y,Xu M,Zhou H P,Shen Y B,Chen Q Y,Ding Y C,Zhu W J 2007 Acta Phys.Sin.56 5359(in Chinese)[段满益,徐明,周海平,沈益斌,陈青云,丁迎春,祝文军2007物理学报56 5359]