Journal of Crystal Growth 237–239 (2002) 1326–1330 Preparation of ferromagnetic (In,Mn)As with relatively low hole concentration and Curie temperature 50 K T. Slupinski a, * ,1 , A. Oiwa a , S. Yanagi b , H. Munekata a,b a Kanagawa Academy of Science and Technology, KSP East 309, 3-2-1 Sakado, Takatsu-ku, Kawasaki 213-0012, Japan b Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan Abstract Ferromagnetic (In,Mn)As/GaSb and (In,Ga,Mn)As/GaSb heterostructures with Mn composition x ¼ 0:0320:09 have been prepared by molecular beam epitaxy. It is found that the relation between maximum Curie temperature T C and Mn content x can be expressed experimentally by T C ¼ 800x up to about T C ¼ 50 K within the limit of this study. The hole concentration sufficient for T C ¼ 50 K is found to be several times lower than the value shown in the existing theory (Science 287 (2000) 1049). Formation of structural pairs of Mn atoms (or few-atomic aggregates) in some close lattice sites is discussed to explain the observed results. r 2002 Elsevier Science B.V. All rights reserved. PACS: 73.61.Ey; 75.50.Dd; 81.05.Ea Keywords: A1. Impurities; B1. Alloys; B2. Semiconducting III–V materials; B2. Magnetic materials 1. Introduction Realization of (In,Mn)As and (Ga,Mn)As [1–4] has opened studies of a class of new magnetic alloy semiconductors (MAS) based on III–V compounds, and offered the opportunity to combine semiconductors with ferromagnetism. In these systems, the ferromagnetic order appears as a consequence of heavy hole doping. The first observation of ferromagnetism in III–V-MAS was reported for p-(In,Mn)As [4] with Curie tempera- ture T C p7 K and then p-(In,Mn)As-based hetero- structures with T C ¼ 35 K [5]. This was followed by the report on p-(Ga,Mn)As with T C ¼ 110K [6], and the GaAs-based MAS has become a dominant and mostly studied material, partly for the purpose of maximizing its Curie temperature. Recently, however, the importance of (In,Mn)As has been renewed by the demonstrations on control of ferromagnetic order by light illumina- tion [7,8] and by application of an electric field through the gate electrode [9]. Ferromagnetism in III–V-MAS has been de- scribed by the models based on hole-mediated Mn–Mn spin exchange interaction [10–14]. The models discussed in Refs. [10–12] predict higher Curie temperatures for host binary semiconduc- tors having higher effective hole density of states, and thus (Ga,Mn)As is favorable over (In,Mn)As. In this paper, we explore the possibility to increase Curie temperature of (In,Mn)As and compare our experimental results with the existing theoretical/ *Corresponding author. Tel.: +81-44-819-2044; fax: +81- 44-819-2039. E-mail address: tomslu@net.ksp.or.jp (T. Slupinski). 1 On leave from Institute of Experimental Physics, Warsaw University, Poland. 0022-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)02060-7