XAFS study of local disorder in thea−GdxSi1−xamorphous magnetic semiconductor

Abstract

The local structure of an amorphous a-Gd x Si 1Ϫx (xϭ0.04,0.07,0.12,0.18) magnetic semiconductor is determined from combined x-ray absorption fine structure ͑XAFS͒ measurements at the Gd L 3 and Si K absorption edges. XAFS data indicate that the structure is amorphous, with Gd atoms surrounded predominantly by Si atoms, consistent with a random substitution of Gd in the Si network. Gd substitution induces a large local distortion resulting in a Gd-Si distance of 2.98͑3͒ Å compared to a Si-Si distance of 2.39͑1͒ Å. The lack of x dependence in the Gd local environment indicates that the distortions around the Gd do not interact with one another, even at xϭ0.18. In addition, a small but systematic increase in the mean squared disorder of the Si-Si interatomic distance is observed with x. These results suggest that the amorphous Si network is very effective in relaxing the local strain through random displacements of Si atoms within a few Å of the perturbing Gd atoms.

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

“…For group-IV semiconductors, the amorphous structure preserves local tetrahedral four-fold covalent bonding, described by the continuous random network model. [15][16][17][18] Even when doped up to 20-25 at.% with atoms such as Nb, Y or the large magnetic rare-earth ion Gd, a-Si and aGe remain chemically homogeneous and amorphous, as measured by high resolution transmission electron microscopy, EXAFS, EDX, and other chemical and structural analysis tools. [19][20][21] These systems behave as excellent analogues (electronic and optical properties) to crystalline Si:P or Si:B, and have been used to probe many physics and materials science problems, including the T=0 insulator-metal (I-M) transition.…”

Local structures around Mn atoms in MnxSi1-xthin films probed by fluorescence XAFS

“…When the growth temperature of Mn x Si 1-x thin films is under this critical temperature during the magnetron cosputtering (550K), the structure of the Si base approaches to be amorphous with large disorder [19]. When the doped Mn content is low, they tend to homogeneously separate into Si matrix, and randomly substitute the host atoms in the Si network on the substrate, close to those of Gd-doped Si with amorphous structure [20]. As the Mn content reaches 0.15 wt%, the doped Mn atoms are prone to aggregate and react with the Si atoms around them and finally form the energetically more favorable Mn-Si compounds.…”

Local structure of amorphous GaN1−xAsx semiconductor alloys across the composition range

“…The value of N N was similar to N values reported in the literature for other amorphous semiconductors. 15,19 The mean square disorder parameter for the Ga K edge analysis is shown as a function of composition in Figure 7 (bottom). The r 2 parameter was significantly lower for Nrelated bonds compared to As-related bonds, and similar to the r 2 value for the crystalline reference samples.…”

“…14 This technique has been used extensively to study the structural properties of amorphous semiconductors, such as a-Si (and its alloys with Ge, C, and H), a-Ge, and compound semiconductors such as a-GaAs. [15][16][17][18][19][20][21] In this work, we apply the technique of EXAFS to study the local structure of As and Ga atoms in a-GaN 1Àx As x to further develop our understanding a)…”