Synthesis, Characterization and Application of AlGaMnN

University Of Florida, Gainesville FL

Investigators

Abstract

This proposal was received in response to the Spin Electronics for the 21st century Initiative, Program Solicitation NSF 02-036. The proposal focuses on synthesis of n-type dilute magnetic semiconductors based on GaMnN and AlMnN, and on using the resultant materials to fabricate tunneling magnetoresistance (TMR) and spin FET devices. Materials growth and basic understanding of the structural, chemical and electrical properties governing the magnetism will be addressed first. A host of characterization tools will be employed to characterize and provide guidance for the optimization of the materials growth. Quantitative measurements of the magnetization as a function of temperature will be made using a SQUID magnetometer. The degree of magnetic order and the magnetic transition temperature will be ascertained from temperature dependence of the magnetization and susceptibility together with the application of Arrott plots. The roles of the nitrogen/metal ratio, growth rate and growth temperature on material properties will be investigated. In order to determine the composition and microstructure, samples will be characterized using powder and high resolution XRD, TEM and AES. Once the dependence of magnetic properties on growth conditions has been established, experiments will be performed to determine the role of the Mn both physically and electrically. Bonding information will be obtained from EXAFS and XPS. This information will be correlated with Hall measurement, photoluminescence and photoluminescence excitation spectroscopy measurements to determine the position of the Mn level(s) in the bandgap. In general, samples with the same Mn concentration but different magnetic properties will be compared in order to discern any differences chemically, structurally or electrically which can explain the variance in magnetic behavior. One of the important objectives of this program is to look at the role of co-dopant concentration and carrier concentration on the magnetic and electrical behavior of the material. By varying the Si concentration in GaMnN and AlMnN with a fixed Mn concentration, it may be possible to vary the electron concentration independent of the Mn. This would not only allow independent tailoring of the electrical properties and the magnetic properties for device applications, but would also allow investigation of the role of the metal insulator transition in the ferromagnetic ordering. Through the comparison of GaMnN and AlMnN, it will also be possible to test theoretical predictions regarding the relationship between lattice constituents and Curie temperature. Further, because of the DX centers formed by the Si, AlMnN:Si may prove useful as a light activated magnetic material. By illuminating AlMnN:Si with below bandgap light, it may be possible to alter the magnetic properties. Device applications to be pursued in this program include light activated TMR devices using GaMnN spin sources and AlMnN:Si barriers, and spinFETS using conventional AlGaN/GaN HEMTs in which n-GaMnN layers are used as the source and drain regions.