立方BC_2N中杂质行为和氮化铍光学性质的理论研究
|
摘要
本工作采用第一性原理研究了杂质对新型超硬材料c-BC_2N的影响，并对不同结构的氮化铍的相关性质作了系统的研究；针对典型的B-C-N体系，研究了BC_2N体材料的杂质行为及其压力效应，主要研究c-BC_2N中氧原子取代杂质的形成能、电子能级的位置等随压力的变化情况。具体的研究工作介绍如下：
(一)研究了立方BC_2N中氧替代杂质对结构的影响。结果显示，在BC_2N体材料的氧取代杂质中，氧取代氮(O-N)的形成能比较低，比较容易出现在体材料中。而Co元素作为触媒也会经常出现在合成的BC_2N体材料中，其浓度比较高。所以本文也对Co元素的间隙掺杂的电子结构做了研究。
(二)Be与N构成的宽禁带半导体超硬材料有着广阔的应用前景，但由于Be元素有毒，所以其在实验上的进展比较小。本部分工作的主要内容是由第一性原理出发计算研究了Be_3N_2的三种可能结构的能带、态密度、光学性质、动力学性质以及压力对其体弹模量的影响。结果表明，这三种结构都是良好的半导体发光材料。
Diamond is well known for the hardest material which has a notable mechanical property in the world. It has wide applications in the industry for its outstanding optical, thermal, acoustical and electrical properties. For the defects are ineluctably exist in all the crystals, and it can bring new defect electron levels in the forbidden band which makes a decisive effect on the character of the crystal. People have make great effort on the defect and impurity which would bring new level in the forbidden band, and it is consummate day by day, but the theory calculation result could not match the experiment result as well.
In this work, we do a deep research on oxygen substitute in the cubic structures of BC_2N, and have completely theoretical analysis of the structural and electronic properties and the optical property using first-principles method. And the Co atom considered as the accelerant in composing BC_2N has also exist in the BC_2N crystal with a high concentration, so in our work we also do some research on the Co atom as a intrinsic defect; The burgeoning superhard semiconductor material Be_3N_2 with a wide band gap have a wide application foreground, but the Be is a toxin element which lead a small application in experiment, in our calculation we also do a deep research on the band structure, DOS, optical property, and the dynamics property. The main contents are as follows:
Ⅰ. Our first-principles calculations show that it has lower formation energy after Oxygen replace the nitrogen in the c-BC_2N. From the electronic DOS we can see that the band structure has come together and the Fermi level get up a little higher and the DOS move to the lower energy after Nitrogen substituted. With pressure increase, the defect level near the conductive band cut through the Fermi level from F to Z which belongs to the high symmetry point in the BZ, and at the other side from F to Z point, the defect level go far away from the Fermi level which make it easy for the electrons in the defect level activated. It can be seen as the transformation of the semiconductor from P type to N type. The different charge in the O-N structure has also brought different defect level. From the optical calculation on the O-N structure shows that the real part of the dielectric function increase with the energy become larger which has a largest number when the energy come to 6.67eVo The main peak of the refractive index appears at the energy region 2.5-15eV, the largest peak corresponding to the 6.89eV, the extinction number get smaller along with the energy get bigger when the energy bigger than 12.46ev. The intrinsic defect of Co in C-BC_2N has formation energy of9.5eV, the formation volume is 0.9A , which prove that Co is hard to exist in BC_2N as an intrinsic defect and it will make the crystal expand.
Ⅱ. We investigate three different structures of Be_3N_2, the calculated result shows that theα-Be_3N_2 is a direct band semiconductor with a band width of 4.36eV;β-Be_3N_2 is an indirect semiconductor with a band gap of 7.40eV. What's more theγ-Be_3N_2 is a perfect direct semiconductor with a band width of 2.50eV.We also found that the Bulk Modulus ofα-Be_3N_2 andβ-Be_3N_2 increase distinctively compared with theγ-Be_3N_2, and theα-Be_3N_2、β-Be_3N_2 have nearly the same changing trend.
For theα-Be_3N_2, the largest number of the real part of the complex dielectric function appears at 7.0eV, and the imaginary part of complex dielectric function has the largest number of 11.OeV. We also do some optical calculations on this three structures, these results prove that the absorption function of theγ-Be_3N_2 appears three obvious peaks, the first peak has a energy of 10.12eV which comes from the electron transition from the 2s orbit of Be to the 1s orbit of N; the second peak mainly contributed from the 1s obit of Be to the 1s orbit of N with the energy of 15.28eV; the third peak comes from the 1s orbit of Be to 2p orbit of N with the highest energy of 16.88eV.
(一)研究了立方BC_2N中氧替代杂质对结构的影响。结果显示，在BC_2N体材料的氧取代杂质中，氧取代氮(O-N)的形成能比较低，比较容易出现在体材料中。而Co元素作为触媒也会经常出现在合成的BC_2N体材料中，其浓度比较高。所以本文也对Co元素的间隙掺杂的电子结构做了研究。
(二)Be与N构成的宽禁带半导体超硬材料有着广阔的应用前景，但由于Be元素有毒，所以其在实验上的进展比较小。本部分工作的主要内容是由第一性原理出发计算研究了Be_3N_2的三种可能结构的能带、态密度、光学性质、动力学性质以及压力对其体弹模量的影响。结果表明，这三种结构都是良好的半导体发光材料。
Diamond is well known for the hardest material which has a notable mechanical property in the world. It has wide applications in the industry for its outstanding optical, thermal, acoustical and electrical properties. For the defects are ineluctably exist in all the crystals, and it can bring new defect electron levels in the forbidden band which makes a decisive effect on the character of the crystal. People have make great effort on the defect and impurity which would bring new level in the forbidden band, and it is consummate day by day, but the theory calculation result could not match the experiment result as well.
In this work, we do a deep research on oxygen substitute in the cubic structures of BC_2N, and have completely theoretical analysis of the structural and electronic properties and the optical property using first-principles method. And the Co atom considered as the accelerant in composing BC_2N has also exist in the BC_2N crystal with a high concentration, so in our work we also do some research on the Co atom as a intrinsic defect; The burgeoning superhard semiconductor material Be_3N_2 with a wide band gap have a wide application foreground, but the Be is a toxin element which lead a small application in experiment, in our calculation we also do a deep research on the band structure, DOS, optical property, and the dynamics property. The main contents are as follows:
Ⅰ. Our first-principles calculations show that it has lower formation energy after Oxygen replace the nitrogen in the c-BC_2N. From the electronic DOS we can see that the band structure has come together and the Fermi level get up a little higher and the DOS move to the lower energy after Nitrogen substituted. With pressure increase, the defect level near the conductive band cut through the Fermi level from F to Z which belongs to the high symmetry point in the BZ, and at the other side from F to Z point, the defect level go far away from the Fermi level which make it easy for the electrons in the defect level activated. It can be seen as the transformation of the semiconductor from P type to N type. The different charge in the O-N structure has also brought different defect level. From the optical calculation on the O-N structure shows that the real part of the dielectric function increase with the energy become larger which has a largest number when the energy come to 6.67eVo The main peak of the refractive index appears at the energy region 2.5-15eV, the largest peak corresponding to the 6.89eV, the extinction number get smaller along with the energy get bigger when the energy bigger than 12.46ev. The intrinsic defect of Co in C-BC_2N has formation energy of9.5eV, the formation volume is 0.9A , which prove that Co is hard to exist in BC_2N as an intrinsic defect and it will make the crystal expand.
Ⅱ. We investigate three different structures of Be_3N_2, the calculated result shows that theα-Be_3N_2 is a direct band semiconductor with a band width of 4.36eV;β-Be_3N_2 is an indirect semiconductor with a band gap of 7.40eV. What's more theγ-Be_3N_2 is a perfect direct semiconductor with a band width of 2.50eV.We also found that the Bulk Modulus ofα-Be_3N_2 andβ-Be_3N_2 increase distinctively compared with theγ-Be_3N_2, and theα-Be_3N_2、β-Be_3N_2 have nearly the same changing trend.
For theα-Be_3N_2, the largest number of the real part of the complex dielectric function appears at 7.0eV, and the imaginary part of complex dielectric function has the largest number of 11.OeV. We also do some optical calculations on this three structures, these results prove that the absorption function of theγ-Be_3N_2 appears three obvious peaks, the first peak has a energy of 10.12eV which comes from the electron transition from the 2s orbit of Be to the 1s orbit of N; the second peak mainly contributed from the 1s obit of Be to the 1s orbit of N with the energy of 15.28eV; the third peak comes from the 1s orbit of Be to 2p orbit of N with the highest energy of 16.88eV.
引文
[1]A.Y.Liu,M.L.Cohen.Prediction of New Low Compressibility Solids.Science,1989,245:841-842
[2]A.Y.Liu,R.M.Wentzovitch,M.L.Cohen.Atomic Arrangement and Electronic Structureof BC2N.Phys.Rev.B,1989,39(3):1760-1765
[3]Y.Miyamoto,M.L.Cohen,S.G.Louie.Ab Inito Calculation of Phonon Spectra for Graphite,BN,and BC2N Sheets.Phys.Rev.B,1995,52(20):14971-14975
[4]H.Nozaki,S.Itoh.Lattice Dynamics of BC2N.Phys.Rev.B,1996,53(21):14161-14170
[5]Y.Tateyama,T.Ogitsu,K.Kusakabe,et.al.Proposed Synthesis Path for Heterodiamond BC2N.Phys.Rev.B,1997,55(16):10161-10164
[6]A.Y.Liu,R.M.Wentzovitch,M.L.Cohen.Atomic Arrangement and Electronic Structureof BC2N.Phys.Rev.B,1989,39(3):1760-1765
[7]M.Kawaguchi.B/C/N Materials Based on the Graphite Network.Adv.Mater.,1997,9,8:615-625
[8]R.Q.Zhang,K.S.Chan,H.F.Cheung,et al.Appl.Phys.Lett.,1999,75:2259-2261.
[9]M.Mattesini and S.F.Matar.First-principles characterisation of new ternary heterodiamondBC2N phases.Matar,Comput.Mater.Sci.,2001,20:107-119
[10]M.Mattesini and S.F.Matar,Search for ultra-hard materials: theoretical characterization of novel
[11] C.W.Ong, K.F.Chan, X.A.Zhao, et.al. Physical Properties of Room Temperature Deposited B-C-N-O Films Prepared by Dual-ion-beam Deposition. Surface and Coatings Technology, 1999, 115: 145-152
[12] 陈万金，华中，姚斌，等．非晶BCN的制备及其导电性．金属学报，1999，35(5):469-472
[13] Y. Chen, J.C. Barnard, R.E. Palmer, et.al. Indirect Band Gap of Light-emitting BC_2N. Phys. Rev. Lett., 1999, 83(12): 2406-2408
[14] M. O. Watanabe, S. Itoh, K. Mizushima. Bonding characterization of BC_2N thin film. Appl Phys Lett, 1996, 68:2962-2964
[15] Hong Sun, Seung-Hoon Jhi, David Roundy, Structural forms of cubic BC_2N, PRB, 64, 094108
[16] 刘恩科《半导体物理》，高等教育出版社，2001
[17] 韩汝琦，黄昆，《固体物理学》，高等教育出版社，1988．
[18] 谢希德，陆栋，《固体能带理论》，复旦大学出版社，1998．
[19] F. Reif, Fundamentals of Statistical and Thermal Physics, McGraw-Hill, New York, 1965.
[20] S. B. Zhang and J. E. Northrup, Chemical potential dependence of defect formation energies in GaAs: Application to Ga self-diffusion, Phys. Rev. Lett., 1991, 67(17):2339-2342.
[21] D.B. Laks, C.G. Van de Walle, G.F. Neumark, P.E. Bl(?)chl, S.T. Pantelides, Native defects and self-compensation in ZnSe, Phys. Rev. B, 1992, 45(19): 10965-10978.
[22] 张光寅，蓝国祥，王玉芳．晶格振动光谱学．高等教育出版社，第二版，2001:146．
[23] 李正中，《固体理论》，高等教育出版社，北京，1985．
[24] 士杰，韩圣浩，《凝聚态物理》，山东教育出版社，济南，2001
[25] T.Sasaki, M. Akaishi, S. Yamaoka, et. al. Simultaneous Crystallization of Diamond and Cubic Boron Nitride from the Graphite Relative BC_2N under High Pressure High Temperature Conditions. Chem. Mater, 1993 5: 695-699
[26] Armando Reyes-Serrato and Miguel Avalos Borja, Ab initio determination of the electronic structure of beryllium-, aluminum-,and magnesium-nitrides: A comparative study
[27] Mokhtari A, Akbarzadeh H, Electronic and structural properties of beta-Be_3N_2, Physica B —Condensed Matter 324(1-4)
[28] Armanta, MGM; Reyes-Serrato, A Direct wide band gap material: a Hartree-Fock study of alpha-Be_3N_2, COMPUTATIONAL MATERIALS SCIENCE 21:1.
[29] M. Born and K. Huang, Dynamical Theory of Crystal Lattices. Oxford University Press, Oxford, (1954)
[30] C. C. J. Roothaan, New Developments in Molecular Orbital Theory, Rev. Mod. Phys. 1951, 23(2):69-89.
[31] J. C. Slater, A Simplification of the Hartree-Fock Method, Phys. Rev. 1951, 81(3):385-390.
[32] J. A. Pople and R. K. Nesbet, Self-Consistent Orbitals for Radicals, J. Chem. Phys. 1954, 22:571-572.
[33] H. Thomas, The calculation of atomic fields, Proc. Camb. Phil. Soc.1927,23:542.
[34]E.Fermi,A statistical method for determining some properties for the atom,Accad.Naz.Lincei,1927,6:602.
[35]John P.Perdew.Accurate Density Functional for the Energy:Real-Space Cutoff of the Gradient Expansion for the Exchange Hole.Phys.Rev.Lett.,1985,55(16):1665-1668.
[36]John P.Perdew et al.Atoms,molecules,solids,and surfaces:Applications of the generalized gradient approximation for exchange and correlation,Phys.Rev.B,1992,46(11):6671-6687.
[37]John P.Perdew,Kieron Burke,and Matthias Ernzerhof,Generalized Gradient Approximation Made Simple,Phys.Rev.Lett.,1996,77(18):3865-3868.
[38]W.Kohn and L.J.Sham,Self-consistent equations including exchange and correlation effects,Phys.Rev.1965,140(4A):A1133-A1138.
[39]D.J.Singh,Plane waves pseudopotentials and the LAPW method,Kluwer Academic Publishers,Boston,1993.
[40]O.K.Anderson,Linear methods in band theory,Phys.Rev.B,1975,12(8):3060-3083.
[41]W.E.Pickett,Pseudopotential methods in condensed matter application,North-Holland,Amsterdam,1989.
[2]A.Y.Liu,R.M.Wentzovitch,M.L.Cohen.Atomic Arrangement and Electronic Structureof BC2N.Phys.Rev.B,1989,39(3):1760-1765
[3]Y.Miyamoto,M.L.Cohen,S.G.Louie.Ab Inito Calculation of Phonon Spectra for Graphite,BN,and BC2N Sheets.Phys.Rev.B,1995,52(20):14971-14975
[4]H.Nozaki,S.Itoh.Lattice Dynamics of BC2N.Phys.Rev.B,1996,53(21):14161-14170
[5]Y.Tateyama,T.Ogitsu,K.Kusakabe,et.al.Proposed Synthesis Path for Heterodiamond BC2N.Phys.Rev.B,1997,55(16):10161-10164
[6]A.Y.Liu,R.M.Wentzovitch,M.L.Cohen.Atomic Arrangement and Electronic Structureof BC2N.Phys.Rev.B,1989,39(3):1760-1765
[7]M.Kawaguchi.B/C/N Materials Based on the Graphite Network.Adv.Mater.,1997,9,8:615-625
[8]R.Q.Zhang,K.S.Chan,H.F.Cheung,et al.Appl.Phys.Lett.,1999,75:2259-2261.
[9]M.Mattesini and S.F.Matar.First-principles characterisation of new ternary heterodiamondBC2N phases.Matar,Comput.Mater.Sci.,2001,20:107-119
[10]M.Mattesini and S.F.Matar,Search for ultra-hard materials: theoretical characterization of novel
[11] C.W.Ong, K.F.Chan, X.A.Zhao, et.al. Physical Properties of Room Temperature Deposited B-C-N-O Films Prepared by Dual-ion-beam Deposition. Surface and Coatings Technology, 1999, 115: 145-152
[12] 陈万金，华中，姚斌，等．非晶BCN的制备及其导电性．金属学报，1999，35(5):469-472
[13] Y. Chen, J.C. Barnard, R.E. Palmer, et.al. Indirect Band Gap of Light-emitting BC_2N. Phys. Rev. Lett., 1999, 83(12): 2406-2408
[14] M. O. Watanabe, S. Itoh, K. Mizushima. Bonding characterization of BC_2N thin film. Appl Phys Lett, 1996, 68:2962-2964
[15] Hong Sun, Seung-Hoon Jhi, David Roundy, Structural forms of cubic BC_2N, PRB, 64, 094108
[16] 刘恩科《半导体物理》，高等教育出版社，2001
[17] 韩汝琦，黄昆，《固体物理学》，高等教育出版社，1988．
[18] 谢希德，陆栋，《固体能带理论》，复旦大学出版社，1998．
[19] F. Reif, Fundamentals of Statistical and Thermal Physics, McGraw-Hill, New York, 1965.
[20] S. B. Zhang and J. E. Northrup, Chemical potential dependence of defect formation energies in GaAs: Application to Ga self-diffusion, Phys. Rev. Lett., 1991, 67(17):2339-2342.
[21] D.B. Laks, C.G. Van de Walle, G.F. Neumark, P.E. Bl(?)chl, S.T. Pantelides, Native defects and self-compensation in ZnSe, Phys. Rev. B, 1992, 45(19): 10965-10978.
[22] 张光寅，蓝国祥，王玉芳．晶格振动光谱学．高等教育出版社，第二版，2001:146．
[23] 李正中，《固体理论》，高等教育出版社，北京，1985．
[24] 士杰，韩圣浩，《凝聚态物理》，山东教育出版社，济南，2001
[25] T.Sasaki, M. Akaishi, S. Yamaoka, et. al. Simultaneous Crystallization of Diamond and Cubic Boron Nitride from the Graphite Relative BC_2N under High Pressure High Temperature Conditions. Chem. Mater, 1993 5: 695-699
[26] Armando Reyes-Serrato and Miguel Avalos Borja, Ab initio determination of the electronic structure of beryllium-, aluminum-,and magnesium-nitrides: A comparative study
[27] Mokhtari A, Akbarzadeh H, Electronic and structural properties of beta-Be_3N_2, Physica B —Condensed Matter 324(1-4)
[28] Armanta, MGM; Reyes-Serrato, A Direct wide band gap material: a Hartree-Fock study of alpha-Be_3N_2, COMPUTATIONAL MATERIALS SCIENCE 21:1.
[29] M. Born and K. Huang, Dynamical Theory of Crystal Lattices. Oxford University Press, Oxford, (1954)
[30] C. C. J. Roothaan, New Developments in Molecular Orbital Theory, Rev. Mod. Phys. 1951, 23(2):69-89.
[31] J. C. Slater, A Simplification of the Hartree-Fock Method, Phys. Rev. 1951, 81(3):385-390.
[32] J. A. Pople and R. K. Nesbet, Self-Consistent Orbitals for Radicals, J. Chem. Phys. 1954, 22:571-572.
[33] H. Thomas, The calculation of atomic fields, Proc. Camb. Phil. Soc.1927,23:542.
[34]E.Fermi,A statistical method for determining some properties for the atom,Accad.Naz.Lincei,1927,6:602.
[35]John P.Perdew.Accurate Density Functional for the Energy:Real-Space Cutoff of the Gradient Expansion for the Exchange Hole.Phys.Rev.Lett.,1985,55(16):1665-1668.
[36]John P.Perdew et al.Atoms,molecules,solids,and surfaces:Applications of the generalized gradient approximation for exchange and correlation,Phys.Rev.B,1992,46(11):6671-6687.
[37]John P.Perdew,Kieron Burke,and Matthias Ernzerhof,Generalized Gradient Approximation Made Simple,Phys.Rev.Lett.,1996,77(18):3865-3868.
[38]W.Kohn and L.J.Sham,Self-consistent equations including exchange and correlation effects,Phys.Rev.1965,140(4A):A1133-A1138.
[39]D.J.Singh,Plane waves pseudopotentials and the LAPW method,Kluwer Academic Publishers,Boston,1993.
[40]O.K.Anderson,Linear methods in band theory,Phys.Rev.B,1975,12(8):3060-3083.
[41]W.E.Pickett,Pseudopotential methods in condensed matter application,North-Holland,Amsterdam,1989.