Spin Electronics: III-V/Mn Ferromagnetic Semiconductors for Device Application

0224206 Luo This proposal was received in response to the Spin Electronics for the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on growth, characterization and device studies of III-V/Mn materials and their heterostructures. The goal of this program is to develop ferromagnetic resonant interband tunneling diodes (FRITD) and polarization tunable infrared light emitting diodes. In order to develop optimized materials for these devices, and to demonstrate proof of principle operation, device structures will be fabricated and tested in parallel with the materials growth to provide direct feedback to the materials effort. Preliminary studies at the University at Buffalo (UB) of structural, transport/magneto-transport, optical and magnetic properties of the constituent materials for these devices have revealed several interesting problems associated with the incorporation of magnetic Mn++ ions at high sheet densities. More importantly, it was found that the structural, optical, transport and magnetic properties of these materials are closely connected. These studies demonstrate the need for designing materials from the atomic level so that electrical transport, optical and magnetic properties are simultaneously optimized; this is one of the key tasks of this program. Specifically, to tackle these complex problems, it is proposed to form a multidisciplinary research team to carry out comprehensive studies of III-V-based ferromagnetic materials/structures, fundamental properties, spin injection/interface effects and devices. In this proposed work, the University at Buffalo group will: 1) fabricate systematic sets of samples of GaAs/Mn, GaSb/Mn, and InAs/Mn digital alloys, in which submonolayers of Mn are inserted in the III-V lattice; 2) explore the magnetic, electrical transport, optical properties and structural quality as a function of growth conditions; 3) optimize growth conditions to produce the highest Curie temperatures; 4) fabricate and test device structures. The program is formulated to maximize student involvement in multidisciplinary research by engaging engineering and physics students working together to reach common goals. It will utilize existing infrastructure, both for collaborative research and for student interactions, which has been established for the on-going spintronic materials development project supported by the Defense Advanced Research Project Agency (DARPA) focusing on other materials. A total of three full-time graduate students will be supported in this program, a substantial effort made possible by the synergism with the related work. The success of this program will have immediate impact on the key problems in the area of spintronics, namely, improving the Curie temperature and producing materials suitable for practical devices and spin injection into semiconductor heterostructures. Combined with the other materials currently studied in the DARPA-supported project, the materials effort at UB represents one of the strongest in the country. The device fabrication and characterization will lead the way in resolving bottlenecks in materials research related to spin-injection involving III-V materials, and the possibility of electron (rather than hole) spin injection.