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Distinct local electronic structure and magnetism for Mn in amorphous Si and Ge

机译:非晶硅和锗中锰的独特局部电子结构和磁性

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摘要

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 (<0.1μ_B) in amorphous Si (a-Si) to a large distinct local Mn moment (≥3μ_B) 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 N_c 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 Nc and the magnitude of the local moment is essentially independent of the matrix; the local Mn moments approach zero when N_c>7 for both a-Si and a-Ge.
机译:过渡金属(例如Mn)由于其部分填充的d壳,通常在共价半导体中具有较大的局部矩。然而,IV族半导体中的Mn磁化比通常所见更为复杂。在这里,我们报道了在宽范围的Mn浓度范围内,从非晶态Si(a-Si)中的淬火Mn矩(<0.1μ_B)到非晶态Ge(a-Ge)中的较大的局部Mn矩(≥3μ_B)的惊人跨越。 (0.005-0.20)。在d壳电子结构和霍尔效应的征兆中观察到相应的差异。密度泛函理论计算显示出不同的局部结构,分别与针对a-Si和a-Ge测得的不同原子密度一致,并且发现Mn配位数N_c是关键因素。尽管非晶态结构,a-Si中的Mn处于相对明确的高配位间隙型位点,具有宽的d带,低矩和电子(n型)载流子,而a-Ge中的Mn处于低位配位具有较大局部力矩和空穴(p型)载体的替代型位点。而且,Nc和局部力矩的大小之间的相关性基本上与矩阵无关。当a-Si和a-Ge的N_c> 7时,局部Mn矩接近零。

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