| AVS 66th International Symposium & Exhibition | |
| Materials and Processes for Quantum Information, Computing and Science Focus Topic | Monday Sessions |
| Session QS+EM+MN+NS+VT-MoA |
| Session: | Systems and Devices for Quantum Computing |
| Presenter: | Thomas McJunkin, University of Wisconsin - Madison |
| Authors: | T.W. McJunkin, University of Wisconsin - Madison E.R. MacQuarrie, University of Wisconsin - Madison S.F. Neyens, University of Wisconsin - Madison B. Thorgrimsson, University of Wisconsin - Madison J. Corrigan, University of Wisconsin - Madison J.P. Dodson, University of Wisconsin - Madison D.E. Savage, University of Wisconsin - Madison M.G. Lagally, University of Wisconsin - Madison R. Joynt, University of Wisconsin - Madison M. Friesen, University of Wisconsin - Madison S.N. Coppersmith, University of Wisconsin - Madison M.A. Eriksson, University of Wisconsin - Madison |
| Correspondent: | Click to Email |
In recent years, silicon-based quantum dots have been shown to be a promising avenue for quantum computing. However, dots formed in silicon quantum wells exhibit a near-degeneracy of the two low-lying valley states. Motivated by a desire to increase the magnitude and tunability of this valley splitting, we report the characterization of a novel Si/SiGe heterostructure grown with a thin layer of SiGe embedded within the Si quantum well, near the top of the well. The Si/SiGe heterostructure is grown via UHV-CVD on a linearly graded SiGe alloy with a final Ge concentration of 29%. STEM measurements reveal the quantum well structure to consist of a ~10 nm Si layer, followed by a thin ~1 nm SiGe layer, and subsequent ~2 nm layer of pure Si. Above this quantum well, a ~35 nm layer of SiGe with 29% Ge is grown to separate the quantum well from the surface. The intent of this ~1 nm layer of SiGe, positioned just below the upper interface of the quantum well, is to modify the valley splitting of electrons in a 2-dimensional electron gas (2DEG) that reside near this interface. By modifying an external vertical electric field, the electron wavefunction can be moved on and off this spike in germanium concentration.
We report electronic measurements of both Hall bars and quantum dot devices that are fabricated on this heterostructure. Shubnikov-de Haas (SdH) and quantum Hall (QH) measurements reveal a peak transport mobility in excess of 100,000 cm2/(V s) at 6 x 1011 cm-2 carrier density . We report SdH and QH measurements over a wide range of carrier density and magnetic field in the form of a fan diagram. Valley splitting values are measured in the quantum dot device by magnetospectroscopy, in which a few-electron dot transition is measured as the in-plane magnetic field is swept. Measuring at the second, third, and fourth electron transition in the quantum dot, we find valley splittings of 29, 48, and 65 ueV, respectively. To measure tunability of valley splitting, nearby gate voltages are changed to vary the vertical electric field at constant charge occupation. We find that both the lowest lying valley splitting and the valley splitting in the first excited orbital can be tuned over a factor of 2 by means of such changes in gate voltage.