Discipline: Technology and Engineering
Subcategory: Materials Science
William Huang - University of California San Diego
Co-Author(s): John Archibald Peters and Bruce Wessels, Northwestern University, Evanston IL
Spin-diode logic architectures using magnetoresistive semiconductor diodes are an attractive alternative to CMOS technologies, which are approaching the limits of scaling. Magnetically controlled spin-diode circuits use less devices than comparable CMOS circuits, resulting in increased speed and logic density with decreased power dissipation and fabrication complexity. InMnSb is a promising magnetic semiconductor material for spin-diode applications due to its strong exchange coupling and magnetoresistance, however low temperature characterization of magnetoresistance is necessary to obtain a greater understanding of spin splitting in the band structure. A reduction of switching field is also of interest for spin-diode logic and may be observed at low temperature; current InMnSb devices require 15 T for a 50% current reduction at 298 K, whereas a practical device would ideally require less than 1 T to switch resistive states. Magnetotransport measurements were performed on previously fabricated devices consisting of a 200 nm p-InMnSb film epitaxially grown on an n-InSb substrate and patterned into a mesa diode structure with a diameter of 250 μm, under fields ranging from 0 T to 0.88 T and temperatures from 100 K to 7.2 K. Conductance data are then fitted to a twoband conductance model and the spin splitting parameter geff is extracted. We measure a temperature-dependent positive magnetoresistance along with switching behavior with an applied field of 0.5 T at 7.2 K. Mean field theory predicts an increase in spin splitting and geff as temperature decreases, however our measured trend in geff shows a decrease in spin splitting at lower temperatures, possibly due to changes in diode I-V behavior at low temperatures. Despite unexpected trends in geff, our demonstration of switching at less than 1 T has important implications for spin-diode logic as a CMOS alternative. Future work includes measuring devices at lower temperatures to observe if trends in geff persist, and to achieve lower switching fields at higher temperatures, which may be realized by increasing Mn dopant levels.
References: 1. Friedman, J. S., Rangaraju, N., Ismail, Y. I. & Wessels, B. W. A Spin-Diode Logic Family. IEEE Trans. Nanotechnol. 11, 1026–1032 (2012). 2. P
Peters, J. A., Rangaraju, N., Feeser, C. & Wessels, B. W. Spindependent magnetotransport in a p-InMnSb/n-InSb magnetic semiconductor heterojunction. Appl. Phys. Lett. 98, 15–18 (2011).
Funder Acknowledgement(s): This work was supported by the NSF under grant DMR-1305666. We acknowledge the use of the microfabrication facility at Northwestern University, under NSF Grant No. DMR-1121262.
Faculty Advisor: Bruce Wessels,