Imaging spin injection and transport in semiconductor 'spintronic" devices

Monday, February 2, 2009 (All day)
Dr.Scott Crooker

Three essential elements of a semiconductor spin transport device are i) an efficient mechanism for electrically injecting spin-polarized electrons into a semiconductor, ii) a practical means for spinmanipulation and transport, and iii) a simple electronic scheme for detecting the resulting spin polarization. This talk will address each of these three elements in turn using data from low-temperature, magneto-optical scanning Kerr microscopy studies. [1] In these experiments, we directly image the drift, diffusion, and precession of spin-polarized electrons flowing laterally in hybrid GaAs devices having iron (Fe) Schottky tunnel-barrier contacts. The 2D images reveal efficient electrical spin injection extending out to 120 microns in the n:GaAs channel, and an accumulation of spins within a spin diffusion length of a drain contact. Moreover, optical and all-electrical studies show that these Fe/GaAs contacts can also be used as tunable electrical spindetectors in addition to their role as spin injectors.

Time permitting, this talk will also describe a related approach to measure the dynamics of electronspins by simply “listening” to their intrinsic spin fluctuations -- that is, without ever perturbing themfrom thermal equilibrium. Using an ultra-sensitive optical magnetometer
based on Faraday rotation,this approach -- originally applied to warm atomic vapors [2] -- is now being used to measure the inherent “spin noise” of free electrons in semiconductors. [1]

Science 309, 2191 (2005); Nature Physics 3, 197 (2007); arXiv:0809.1120 . [2] Nature 431, 49 (2004).