Abstract

The orientation of electron magnetic moment, called “spin”, could replace charge level as the physical basis of Boolean logic in semiconductor circuits. Silicon has an electronic structure which gives it superior intrinsic advantages as the materials basis for spin electronics, or “spintronics”, and there is a huge existing capital investment in silicon for microelectronics. For these reasons, many attempts were made by others over the past decade to demonstrate the basics of spin injection, spin transport and spin detection in silicon. However, these previous efforts failed.

By utilizing the hot-electron ballistic spin filtering effect in ferromagnetic metal thin films, spin transport in silicon has finally been achieved. This dissertation details our accomplishment, including the necessary development of theoretical modeling of spin transport comprising spin precession and dephasing. The first silicon spintronic device, composed of a tunnel junction as an all-electrical spin injector and a semiconductor/metal/semiconductor spin detector, will be presented in detail from the design and fabrication to electrical and magnetic characterization. Our initial results show coherent spin transport through 10μm of undoped single-crystal silicon with 1% spin polarization. Further improvements in device design, resulting in spin injection efficiency increase to 37%, was employed to demonstrate the first semiconductor spin field effect transistor (spinFET). Using spin transport through an entire silicon wafer (350 μm), the temperature-dependent spin lifetime in undoped silicon was determined, indicating a longitudinal spin lifetime of over 500ns at 60K. In addition, spin transport in n-type doped silicon was explored. The consequences of these results for spintronics applications will be discussed.