TY - JOUR
T1 - Distinct local electronic structure and magnetism for Mn in amorphous Si and Ge
AU - Zeng, Li
AU - Cao, J. X.
AU - Helgren, E.
AU - Karel, J.
AU - Arenholz, E.
AU - Ouyang, Lu
AU - Smith, David
AU - Wu, R. Q.
AU - Hellman, F.
PY - 2010/10/14
Y1 - 2010/10/14
N2 - Transition metals such as Mn generally have large local moments in covalent semiconductors due to their partially filled d shells. However, Mn magnetization in group-IV semiconductors is more complicated than often recognized. Here we report a striking crossover from a quenched Mn moment (<0.1 μB) in amorphous Si (a-Si) to a large distinct local Mn moment (≥3 μB) in amorphous Ge (a-Ge) over a wide range of Mn concentrations (0.005-0.20). Corresponding differences are observed in d -shell electronic structure and the sign of the Hall effect. Density-functional-theory calculations show distinct local structures, consistent with different atomic density measured for a-Si and a-Ge, respectively, and the Mn coordination number Nc is found to be the key factor. Despite the amorphous structure, Mn in a-Si is in a relatively well-defined high coordination interstitial type site with broadened d bands, low moment, and electron (n -type) carriers, while Mn in a-Ge is in a low coordination substitutional type site with large local moment and holes (p -type) carriers. Moreover, the correlation between N c and the magnitude of the local moment is essentially independent of the matrix; the local Mn moments approach zero when Nc >7 for both a-Si and a-Ge.
AB - Transition metals such as Mn generally have large local moments in covalent semiconductors due to their partially filled d shells. However, Mn magnetization in group-IV semiconductors is more complicated than often recognized. Here we report a striking crossover from a quenched Mn moment (<0.1 μB) in amorphous Si (a-Si) to a large distinct local Mn moment (≥3 μB) in amorphous Ge (a-Ge) over a wide range of Mn concentrations (0.005-0.20). Corresponding differences are observed in d -shell electronic structure and the sign of the Hall effect. Density-functional-theory calculations show distinct local structures, consistent with different atomic density measured for a-Si and a-Ge, respectively, and the Mn coordination number Nc is found to be the key factor. Despite the amorphous structure, Mn in a-Si is in a relatively well-defined high coordination interstitial type site with broadened d bands, low moment, and electron (n -type) carriers, while Mn in a-Ge is in a low coordination substitutional type site with large local moment and holes (p -type) carriers. Moreover, the correlation between N c and the magnitude of the local moment is essentially independent of the matrix; the local Mn moments approach zero when Nc >7 for both a-Si and a-Ge.
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U2 - 10.1103/PhysRevB.82.165202
DO - 10.1103/PhysRevB.82.165202
M3 - Article
AN - SCOPUS:78149234865
SN - 1098-0121
VL - 82
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 16
M1 - 165202
ER -