Distribution of Mn in ferromagnetic (In,Mn)Sb films grown on (0 0 1) GaAs using MBE Lien Tran a,n , Fariba Hatami a , W.T. Masselink a , Jens Herfort b , Achim Trampert b a Department of Physics, Humboldt University, Newton Street 15, 12489 Berlin, Germany b Paul-Drude Institute, Hausvogteipaltz 5–7, 10117 Berlin, Germany article info Available online 27 October 2010 Keywords: A3. Molecular beam epitaxy B1. Manganites B2. Magnetic materials B2. Semiconducting indium compounds abstract We characterize structural and magnetic properties of the dilute magnetic semiconductor (In,Mn)Sb grown on GaAs (0 0 1) by molecular beam epitaxy. The films have surface features consisting of dense orthogonally oriented strain-driven hillocks. In addition, triangularly shaped hillocks, presumed to be MnSb clusters, are observed with diameters in the range of 200 nm. The density and size of these triangular hillocks depend strongly on the Mn content. X-ray scattering shows that the presence of Mn in the InSb films decreases the average lattice constant as well as the degree of relaxation of the (In,Mn)Sb films. The distribution of Mn is also investigated by cross-sectional transmission electron microscopy. Two regions are observed: a (In,Mn)Sb film with small defect density and MnSb clusters on the surface. Magnetization measurements indicate that both the (In,Mn)Sb alloy as well as the MnSb inclusions are ferromagnetic. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Diluted magnetic semiconductors (DMS) are characterized by the random substitution of a fraction of original atoms by magnetic atoms. Therefore, magnetic properties with semiconducting prop- erties are combined. The III–V DMS have been extensively studied, particularly those alloys with the smallest lattice constants and largest energy gaps such as (Ga,Mn)As and (Ga,Mn)N, respectively, which are expected to possess the highest Curie temperatures T c . It is also very important to explore the opposite extreme of the family, (In,Mn)Sb, because it opens opportunities for applications in spin- photonics in the far infrared and, due to its high carrier mobility, in devices based on spin-dependent transport. However, there is still not much studied about bulk (In,Mn)Sb DMS crystals [1,2]. Recently, Ganesan and Bhat [3] reported studies on bulk Mn-doped InSb materials grown by the horizontal Bridgman technique. They found that one ferromagnetic phase below 10 K arises from the (In,Mn)Sb alloy, while other ferromagnetic phase results from MnSb clusters in the crystals. In this paper, we describe the distribution of Mn atoms in (In,Mn)Sb films grown on GaAs (0 0 1) by molecular beam epitaxy (MBE). Our results also show the presence of two magnetic phases in the system, due to the (In,Mn)Sb alloy and clusters of MnSb. The presence of such ferromagnetic clusters in these hybrid systems may be important for semiconductor-based spin-photonics applications and devices with a higher Curie temperature. 2. Experimental procedure The (In,Mn)Sb films were grown on semi-insulating epi-ready (0 0 1) GaAs substrates using a Riber Compact 21T MBE system equipped with reflection high energy electron diffraction (RHEED). A VEECO valved cracker cell was used as the Sb source. Before initiating the Mn flux, 0.4 mm thick InSb buffer layer was grown at a manipulator temperature of 350 1C at a growth rate of 2 ˚ A/s and Sb/ In flux ratio of about 5. Based on an absolute temperature calibration that was done for significantly higher temperatures, we estimate the actual surface temperature to be about 310 1C. This temperature was earlier determined to be optimum in our MBE system for InSb/GaAs growth [11]. A (2  4) reconstruction of the RHEED pattern was observed during the growth of the InSb. The (In,Mn)Sb layer was deposited under the same conditions as those of the InSb layer, generally with a thickness of 0.4 mm. Samples were used in this study with various Mn concentrations corre- sponding to different temperatures of the Mn effusion cell. The Mn concentrations were estimated from the Mn/In flux ratio and confirmed by using a dynamical simulation of rocking curve analysis to be about 0.7%, 0.4%, and 0.2% for the samples grown with Mn effusion cell temperatures of T Mn ¼ 670, 600, and 560 1C, respectively. The structural properties were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction. The Hall measurements were carried Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.10.127 n Corresponding author. E-mail address: lien.tran@physik.hu-berlin.de (L. Tran). Journal of Crystal Growth 323 (2011) 340–343