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In recent years, GaN doped with Gd (GaN:Gd) has attracted much attention due to its potential applications in spintronic devices since the high temperature ferromagnetism and the colossal magnetic moment were observed in GaN:Gd. However, the microscopic nature of ferromagnetism in GaN:Gd still is controversial. We investigate the crystal parameters, magnetic moment, formation energies, and electronic structures of the defect complexes formed by Gd and native Ga (or N) vacancies in GaN by using the first-principles method based on the density functional theory. The calculated results show that the energy band gap of GaN:Gd becomes indirect and its width becomes small compared with that of GaN. The lattice constants of GaN:Gd expand due to the larger ionic radius of Gd than that of Ga atom, while they shrink when the Gd atom and Ga vacancies coexist. In the case of the isolated Gd dopant, the Gd-4f electrons lead to a magnetic moment of about 7 B in GaN:Gd. For the defect complex, one Ga vacancy can introduce a magnetic moment of about 2 B, while N vacancy has little effect on the total magnetic moment. In addition, when we focus on the defect complex composed of Gd and five neighboring Ga vacancies, we find that the magnetic moment of per Gd atom and the total magnetic moment depend strongly on the concentration and position of Ga vacancies. When the Ga vacancies are distributed loosely near the Gd atom, the magnetic moment of Gd atom increases slightly, while for the closely-distributed Ga vacancies the Gd magnetic moment can be increased by 2 B. We infer that the interactions among Ga vacancies result in the large magnetic moment of Gd atom. It is also found that the formation energy is very small when the Ga vacancies are distributed thickly around the Gd atom in GaN:Gd. Our results are in qualitative agreement with the results from other studies (Thiess A et al. 2012 Phys. Rev. B 86 180401; Thiess A et al. 2015 Phys. Rev. B 92 104418), where Ga vacancies were proposed to tend to cluster in GaN:Gd and induce the large magnetic moment of Gd. Moreover, the effect of distance between the Gd atom and Ga vacancies on the Gd magnetic moment is also discussed. It is found that the Gd magnetic moment is relatively large when Ga vacancies are close to the Gd atoms.
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Keywords:
- GaN /
- rear-earth doping /
- electronic structure /
- magnetism
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[3] Wang T X, Li Y, Liu Y M 2011 Phys. Stat. Sol. B 248 1671
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[10] Teraguchi N, Suzuki A, Nanishi Y, Zhou Y K, Hashimoto M, Asahi H 2002 Solid State Commun. 122 651
[11] Dhar S, Brandt O, Ramsteiner M, Sapega V F, Ploog K H 2005 Phys. Rev. Lett. 94 037205
[12] Dhar S, Prez L, Brandt O, Trampert A, Ploog K H, Keller J, Beschoten B 2005 Phys. Rev. B 72 245203
[13] Dhar S, Kammermeier T, Ney A, Perez L, Ploog K H, Melnikov A, Wieck A D 2006 Appl. Phys. Lett. 89 062503
[14] Sofer Z, Sedmidubsky D, Moram M, Mackov A, Maryko M, Hejtmnek J, Buchal C, Hardtdegen H, Vcla M, Peřina V, Groetzschel R, Mikulics M 2011 Thin Solid Films 519 6120
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[16] Wang M N, Li Q Q, Li Y 2013 J. Hebei Univ. Technol. 4 0058 (in Chinese) [王美娜, 李倩倩, 李英 2013 河北工业大学学报 4 0058]
[17] Sanna S, Schmid W G, Frauenheim T, Gerstmann U 2009 Phys. Rev. B 80 104120
[18] Gohda Y, Oshiyama A 2008 Phys. Rev. B 78 161201
[19] Thiess A, Dederichs P H, Zeller R, Blugel S, Lambrecht W R L 2012 Phys. Rev. B 86 180401
[20] Mishra J K, Dhar S, Brandt O 2010 Solid State Commun. 150 2370
[21] Lozykowski H J 1993 Phys. Rev. B 48 17758
[22] Davies R, Abernathy C R, Pearton S J, Norton D P, Ivill M P, Ren F 2009 Chem. Eng. Commun. 196 1030
[23] Filhol J S, Jones R, Shaw M J, Briddon P R 2004 Appl. Phys. Lett. 84 2841
[24] Kresse G, Furthmller J 1996 Phys. Rev. B 54 11169
[25] Larson P, Lambrecht W R L, Chantis A, Schilfgaarde M V 2007 Phys. Rev. B 75 045114
[26] Thiess A, Blugel S, Dederichs P H, Zeller R, Lambrecht W R L 2015 Phys. Rev. B 92 104418
[27] Hou Z F, Wang X L, Ikeda T, Terakura K, Oshima M, Kakimoto M, Miyata S 2012 Phys. Rev. B 85 165439
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[1] Morkoc H 1994 J. Appl. Phys. 76 1363
[2] Davies S, Huang T S, Gass M H, Papworth A J, Joyce T B, Chalker P R 2004 Appl. Phys. Lett. 84 2556
[3] Wang T X, Li Y, Liu Y M 2011 Phys. Stat. Sol. B 248 1671
[4] Kang B S, Kim S, Ren F, Johnson J W, Therrien R J, Rajagopal P, Roberts J C, Piner E L, Linthicum K J, Chu S N G, Baik K, Gila B P, Abernathy C R, Pearton S J 2004 Appl. Phys. Lett. 85 2962
[5] Li Q Q, Hao Q Y, Li Y, Liu G D 2013 Acta Phys. Sin. 62 017103 (in Chinese) [李倩倩, 郝秋艳, 李英, 刘国栋 2013 物理学报. 62 017103]
[6] Li Q Q, Hao Q Y, Li Y, Liu G D 2013 Comput. Mater. Sci. 72 32
[7] Jiang L J, Wang X L, Xiao H L, Wang Z G, Yang C B, Zhang M L 2011 Appl. Phys. A 104 429
[8] Gupta S, Zaidi T, Melton A, Malguth E, Yu H B, Liu Z Q, Liu X T, Schwartz J, Ferguson I 2011 J. Appl. Phys. 110 083920
[9] Jadwisienczak W M, Wang J, Tanaka H, Wu J, Palai R, Huhtinen H, Anders A 2010 J. Rare Earth 6 931
[10] Teraguchi N, Suzuki A, Nanishi Y, Zhou Y K, Hashimoto M, Asahi H 2002 Solid State Commun. 122 651
[11] Dhar S, Brandt O, Ramsteiner M, Sapega V F, Ploog K H 2005 Phys. Rev. Lett. 94 037205
[12] Dhar S, Prez L, Brandt O, Trampert A, Ploog K H, Keller J, Beschoten B 2005 Phys. Rev. B 72 245203
[13] Dhar S, Kammermeier T, Ney A, Perez L, Ploog K H, Melnikov A, Wieck A D 2006 Appl. Phys. Lett. 89 062503
[14] Sofer Z, Sedmidubsky D, Moram M, Mackov A, Maryko M, Hejtmnek J, Buchal C, Hardtdegen H, Vcla M, Peřina V, Groetzschel R, Mikulics M 2011 Thin Solid Films 519 6120
[15] Roever M, Malindretos J, Bedoya-Pinto A, Rizzi A, Rauch C, Tuomisto F 2011 Phys. Rev. B 84 081201
[16] Wang M N, Li Q Q, Li Y 2013 J. Hebei Univ. Technol. 4 0058 (in Chinese) [王美娜, 李倩倩, 李英 2013 河北工业大学学报 4 0058]
[17] Sanna S, Schmid W G, Frauenheim T, Gerstmann U 2009 Phys. Rev. B 80 104120
[18] Gohda Y, Oshiyama A 2008 Phys. Rev. B 78 161201
[19] Thiess A, Dederichs P H, Zeller R, Blugel S, Lambrecht W R L 2012 Phys. Rev. B 86 180401
[20] Mishra J K, Dhar S, Brandt O 2010 Solid State Commun. 150 2370
[21] Lozykowski H J 1993 Phys. Rev. B 48 17758
[22] Davies R, Abernathy C R, Pearton S J, Norton D P, Ivill M P, Ren F 2009 Chem. Eng. Commun. 196 1030
[23] Filhol J S, Jones R, Shaw M J, Briddon P R 2004 Appl. Phys. Lett. 84 2841
[24] Kresse G, Furthmller J 1996 Phys. Rev. B 54 11169
[25] Larson P, Lambrecht W R L, Chantis A, Schilfgaarde M V 2007 Phys. Rev. B 75 045114
[26] Thiess A, Blugel S, Dederichs P H, Zeller R, Lambrecht W R L 2015 Phys. Rev. B 92 104418
[27] Hou Z F, Wang X L, Ikeda T, Terakura K, Oshima M, Kakimoto M, Miyata S 2012 Phys. Rev. B 85 165439
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