Epitaxy of Mn on Si(001): Adsorption, surface diffusion, and magnetic properties studied by density-functional theory

Abstract

Ultrathin films of manganese silicides on silicon are of relevance as a possible material system for building spintronics devices with silicon technology. In order to achieve insight into epitaxial growth of such films on Si͑001͒, total-energy calculations are presented using density-functional theory and the full-potential augmented plane wave plus local orbital method. For adsorption of a single Mn atom on Si͑001͒, we find that binding at the subsurface sites below the Si surface dimers is ϳ0.9 eV stronger than on-surface adsorption. There is an energy barrier of only 0.3 eV for adsorbed Mn to go subsurface, and an energy barrier of 1.2 eV for the reverse process. From the calculated potential-energy surface for the Mn adatom, we conclude that the most stable site on the surface corresponds to the hollow site where Mn is placed between two Si surface dimers. For on-surface diffusion, both along and perpendicular to the Si dimer rows, the Mn atoms have to overcome energy barriers of 0.65 eV. For deposition of 0.5 monolayers ͑ML͒ or more, we find that the Si dimers of the Si͑001͒ surface are broken up, and a mixed MnSi layer becomes the energetically most favorable structure. For coverages above 1 ML, the lowest-energy structure changes to a full Mn subsurface layer, capped by a layer of Si adatoms. We identify this transition with the onset of Mn-silicide formation in an epitaxially stabilized CsCl-like crystal structure. Such MnSi films are found to have sizable magnetic moments at the Mn atoms near the surface and interface, and ferromagnetic coupling of the Mn magnetic moments within the layers. Layer-resolved electronic densities of state are presented that show a high degree of spin polarization at the Fermi level, up to 45% and 27% for films with two or three Si-Mn layers, respectively.

Ab initiostudy of the magnetic ordering in Si/Mn digital alloys

“…20 In this study, Mn was found to be incorporated into Si as an interstitial dopant in good agreement with recent first-principles calculations. [23][24][25] The interstitial Mn was also observed in thin films irradiated by ultraviolet light releasing metal species into the semiconductor substrate. 26 Meanwhile, molecular beam epitaxy produces samples with mostly substitutional Mn in the Si matrix.…”

The growth of manganese layers on Si(100) at room temperature: A photoelectron spectroscopy study

“…In order to circumvent these problems we are investigating the feasibility of a surface-driven approach for the incorporation of Mn into a Si matrix. This approach has been suggested in several theoretical studies, which indicate that selected Mn-Si surface structures, and delta-doped layers of Mn embedded in Si might indeed be ferromagnetic [11,[16][17][18][19][20][21][22][23]. A set of recent STM studies has been geared towards the investigation of the formation of Mn surface structures on the Si(1 0 0) surface [18][19][20]24].…”

Local structure and magnetic properties of B2- and B20-like ultrathin Mn films grown on Si(001)

“…While DFT calculations 30 and scanning tunneling microscopy (STM) experiments 31 show that the subsurface sites are more favorable for Mn on Si(001), STM measurements on Mn deposited at room temperature show that Mn adatoms are energetically inhibited from populating these sites at room temperature and instead form chains on the surface. 32,33 By depositing the capping layer prior to annealing, we enabled interactions between the surface Mn layer and the deposited Si that leads to the formation of a MnSi-B20 phase.…”