Photoemission of Ga_1–xMn_x As with high Curie temperature and transformation into MnAs of zincblende structure

Abstract

Epitaxial films of Ga1–x Mnx As, x = 0.08, with a high ferromagnetic ordering temperature (TC = 160 K) grown and post‐growth annealed at low temperature (LT) have been studied in a photoemission experiment. The (100) surfaces were prepared by wet etching to remove surface segregated interstitials. By resonant photoemission at the Mn M‐edge, the appearence of a Mn induced main peak at 4.5 eV binding energy and an intense satellite at ∼7.2 eV are observed in full agreement with our previous work on Ga1–x Mnx As with TC ∼50 K. Mn induced states are also observed around 1 eV to 2 eV but are of weaker intensity than in our previous work which may indicate a depletion of interstitial Mn. In no stage of surface preparation, emission from the gap region was observed where, according to recent local‐density calculations, interstitial Mn would contribute to the spectra. Additional annealing in situ changes the photoemission spectra strongly: The Mn 3d spectral weight increases altogether and the satellite decreases in intensity relative to the Mn 3d main peak and shifts to ∼6.5 eV. Comparison to the literature indicates that zincblende‐type MnAs is formed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron correlations in MnxGa1–xAs as seen by resonant electron spectroscopy and dynamical mean field theory

“…Refs. [50][51][52][53] the present experiments were carried out on as-grown samples, transferred in ultrahigh vacuum between the growth-and analysis systems. This is an essential difference, since the investigated (Ga,Mn)As material is known to be metastable and its surface cannot be reliably restored by traditional preparation methods like Ar sputtering and annealing.…”

Dilute ferromagnetic semiconductors: Physics and spintronic structures

“…Such a scenario is supported by the study combining synchrotron XRD and a technique of x-ray standingwave fluorescence at grazing incidence (Holý et al, 2006), which shows that (Ga,Mn)As consists of a uniform singlecrystal film covered by a thin surface Mn-rich layer containing Mn atoms at random non-lattice sites. After annealing, the concentration of interstitial Mn and the corresponding lattice expansion of the epilayer are reduced, the effect being accompanied by an increase in the density of randomly distributed Mn atoms in the disordered surface layer (Rader et al, 2009), where Mn ions are oxidized (Edmonds et al, 2004a,b;Olejník et al, 2008;Schmid et al, 2008;Yu et al, 2005).…”

Electronic structure of (Ga,Mn)As as seen by synchrotron radiation

“…In particular, core level photoemission combined with configuration-interaction cluster calculations were used to address the Mn valence and the p-d interaction between Mn impurity and host semiconductors [40]. Since these early experimental reports, many efforts have been focused on reaching a reliable control of surface and interface effects by means of standard surface preparation methods, e.g., sputtering and annealing [26,[97][98][99][100][101]; this is mainly due to the extreme surface sensitivity of PES, which for typical XPS photon energies (∼50-800 eV) results in a probing depth less than 10 Å (see figure 2). In recent years, hard x-ray PES (HAXPES) has become a new tool for the analysis of bulk electronic properties: it offers an information depth of more than 6 nm for electron kinetic energy above 5 keV, corresponding to bulk sensitivity [102,103], thus reducing the uncertainties connected to surface preparation.…”