SPIN-PUMPING-INDUCED SPIN TRANSPORT IN p-TYPE SILICON AT ROOM TEMPERATURE

Spin transport in inorganic semiconductors provides an indispensable building block for realizing the so-called beyond-CMOS technologies. Since the spin-orbit interaction in silicon (Si) is essentially small, Si-based functional devices using the spin degree of freedom is recognized to be promising with respect to spin coherence. Although spin transport at room temperature (RT) in n-Si has been reported [1], spin transport in p-Si has not been experimentally realized, which is an important and unexplored issue in spintronics. Successful observations of spin transport in nand p-Si are significant for constructing future spin-based logic systems, such as for the case of the charge transport in Si for operating conventional logic circuits. We experimentally demonstrated spin-pumping-induced spin current generation and spin transport in p-Si at RT. In the experiments, a ferromagnetic metal Ni80Fe20 film and a paramagnetic metal palladium (Pd) wire were separately formed with the gap distance of ~500 nm on a p-Si substrate with a doping concentration of 1 ́ 10 cm,by using electron beam lithography and electron beam deposition. The sample was placed at the center of a microwave cavity in an electron spin resonance system. In the ferromagnetic resonance condition of the Ni80Fe20 film, a spin current was generated in the p-Si by the spin pumping [2, 3], and the spin current was absorbed into the Pd wire, which was transferred to a charge current by the inverse spin-Hall effect [4] in the Pd wire. The output voltage of 1.4 μV by the charge current at the spin pumping was detected in the Pd wire at RT, under the microwave power of 100 mW, and the voltage sign was inverted by the magnetization reversal of the Ni80Fe20 film. Meanwhile, in the case of samples with a copper wire instead of the Pd wire, no output voltages were observed. This indicated that we successfully observed the spin transport in the p-Si at RT.[5] The spin diffusion length in the p-Si was estimated to be ca. 150 nm at RT.[5]