Ion Beam Synthesis of Transition Metal Nanoclusters in Silicon

The synthesis of materials combining ferromagnetism and semiconducting properties is of great interest for the development of devices for future electronics. Possible implementations of adding the spin degree of freedom to conventional semiconductors are the formation of diluted magnetic semiconductors (DMS's) and the synthesis of magnetic clusters embedded in semiconducting matrices. Despite the technological importance of Si, the former research has mostly been focused on II-VI, III-V and other compound semiconductors. Beside various layer deposition techniques, ion implantation in combination with subsequent thermal treatment is an excellent way to introduce the necessary high concentration of foreign atoms into the substrate. Especially the formation of magnetic clusters in semiconductors or DMS layers is of interest because they offer the possibility to achieve Curie temperatures above room temperature, which is a drawback of common DMS structures. In the present paper we have studied the formation of MnAs and MnSb nanoclusters in Si by co-implantation of Mn, As and Sb in combination with subsequent thermal annealing. In certain windows of the implantation and annealing parameters both Mn and As or Mn and Sb rich crystalline nanoclusters are formed that are partly phase-separated. The influence of the formation parameters on size, size distribution and composition of the nanocrystals as well as the role of atom diffusion are discussed. Results of magnetic analyses are presented as well.