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The optical generation of an out-of-equilibrium spin population is a keystone process for quantum technologies and spintronics alike. Although this is an established technique for studying direct band-gap semiconductors, it has been proven limited in materials that possess weak oscillator strengths for the optical transitions. We address the problem by presenting an all-optical analog of the spin-pumping method. By applying this concept to a Ge-on-Si heterostructure, we observe luminescence from Si with a polarization degree as high as 9%. The progressive etching of the absorbing layer, assisted by magneto-optic experiments, allows us to ascertain that the polarized emission is determined by effective spin injection aided by the carrier lifetime shortening due to extended defects. These findings can facilitate the use of highly promising spin-dependent phenomena of Si, whose optical exploitation has been hampered by fundamental limitations due to its peculiar electronic structure.
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The optical generation of an out-of-equilibrium spin population is a keystone process for quantum technologies and spintronics alike. Although this is an established technique for studying direct band-gap semiconductors, it has been proven limited in materials that possess weak oscillator strengths for the optical transitions. We address the problem by presenting an all-optical analog of the spin-pumping method. By applying this concept to a Ge-on-Si heterostructure, we observe luminescence from Si with a polarization degree as high as 9%. The progressive etching of the absorbing layer, assisted by magneto-optic experiments, allows us to ascertain that the polarized emission is determined by effective spin injection aided by the carrier lifetime shortening due to extended defects. These findings can facilitate the use of highly promising spin-dependent phenomena of Si, whose optical exploitation has been hampered by fundamental limitations due to its peculiar electronic structure.
Strained germanium (๐-Ge) and strained silicon (๐-Si) buried quantum wells have enabled advanced spin-qubit quantum processors. However, in the absence of suitable lattice-matched substrates, ๐-Ge and ๐-Si are deposited on defective, metamorphic SiGe buffers, which may impact device performance and scaling. Here an alternative platform is introduced based on the heterojunction between bulk unstrained Ge and a lattice-matched strained silicon-germanium (๐-SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52-nm-thick ๐-SiGe barrier, a low-disorder two-dimensional hole gas is demonstrated with a high-mobility of 1.33 ร105 cm2/Vs and a low percolation density of 1.4โข(1) ร1010 cmโ2. Quantum transport shows that holes confined in the buried unstrained Ge channel have a strong density-dependent in-plane effective mass and out-of-plane ๐-factor, pointing to a significant heavy-holeโlight-hole mixing in agreement with theory. Measurements of Zeeman-split levels in quantum point contacts further highlight this character, showing a two-fold larger in-plane ๐-factor in Ge than in ๐-Ge. The prospects of strong spinโorbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.
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Strained germanium (๐-Ge) and strained silicon (๐-Si) buried quantum wells have enabled advanced spin-qubit quantum processors. However, in the absence of suitable lattice-matched substrates, ๐-Ge and ๐-Si are deposited on defective, metamorphic SiGe buffers, which may impact device performance and scaling. Here an alternative platform is introduced based on the heterojunction between bulk unstrained Ge and a lattice-matched strained silicon-germanium (๐-SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52-nm-thick ๐-SiGe barrier, a low-disorder two-dimensional hole gas is demonstrated with a high-mobility of 1.33 ร105 cm2/Vs and a low percolation density of 1.4โข(1) ร1010 cmโ2. Quantum transport shows that holes confined in the buried unstrained Ge channel have a strong density-dependent in-plane effective mass and out-of-plane ๐-factor, pointing to a significant heavy-holeโlight-hole mixing in agreement with theory. Measurements of Zeeman-split levels in quantum point contacts further highlight this character, showing a two-fold larger in-plane ๐-factor in Ge than in ๐-Ge. The prospects of strong spinโorbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.
