|
The detection of optically-injected spin-polarized holes by means of inverse spin Hall effect (ISHE) in a Pt/n-doped semiconductor junction is challenging because of the faster spin relaxation of holes compared to electrons at room temperature. Nevertheless, electric fields at the junction arising from the contact potential or an externally-applied bias voltage can favor the transfer of spin-polarized holes repelling electrons from Pt. Here, we report on photo-induced ISHE measurements where spin-polarized holes are detected using two different configurations, namely, i) at low temperature in a Pt/lightly P-doped Si junction, and ii) at 300K in a non-local architecture leveraging graphene as a spin interconnect between Pt and lightly As-doped Ge. Spin-polarized holes are optically oriented with a confocal microscopy setup in the valence band of the semiconductors illuminated with circularly polarized photons with energy above the band gap. In the first device, at T < 22K in Si the spin-relaxation time of holes increases and the majority of phosphorus dopants are not ionized, hence the built-in electric field originating from the potential difference between the work functions of Si and Pt extends to the whole substrate fostering (hampering) the diffusion of holes (electrons) towards Pt. The combination of these two phenomena allows one to measure spin-polarized holes at low temperatures. In the second device, photo-generated spin-polarized holes are successfully transferred to graphene by applying a bias voltage to the graphene/Ge junction. Since graphene is characterized by a significantly-long spin-relaxation time, holes diffuse with negligible spin losses towards Pt where their spin is revealed by means of photo-induced ISHE.
|
