Abstract
The push for a semiconductor-based quantum information technology has renewed interest in the spin states and optical transitions of shallow donors in silicon, including the donor bound exciton transitions in the near-infrared and the Rydberg, or hydrogenic, transitions in the mid-infrared. The deepest group V donor in silicon, bismuth, has a large zero-field ground state hyperfine splitting, comparable to that of rubidium, upon which the now-ubiquitous rubidium atomic clock time standard is based. Here we show that the ground state hyperfine populations of bismuth can be read out using the mid-infrared Rydberg transitions, analogous to the optical readout of the rubidium ground state populations upon which rubidium clock technology is based. We further use these transitions to demonstrate strong population pumping by resonant excitation of the bound exciton transitions, suggesting several possible approaches to a solid-state atomic clock using bismuth in silicon, or eventually in enriched 28Si.
Highlights
Followed by random relaxation to drive population away from the component being pumped
Each of the excited levels is further split by the hyperfine interaction, though by a smaller amount than the ground state
Since the hyperfine splitting occurs in the final state for D0X emission, the relative intensity of the two components in PL reflects the difference in degeneracies of the two hyperfine states (11:9)
Summary
All experiments were carried out with a sample from the same crystal used in the previous PL study[14] It is dislocation-free float-zone grown natural Si doped with Bi with concentration 2 × 1014 cm−3 in a wafer 1 mm thick and 10 mm in diameter, cut perpendicular to the [001] crystal growth axis, and etched in HF/ HNO3 to remove surface damage. For the noncontact PC measurements[3,6] the sample was mounted in a strain-free manner between copper foil electrodes in superfluid He at ~1.5 K, and excited with a tunable single-frequency Yb-doped fiber laser. The PL spectrum was obtained with 532 nm above-gap excitation of the sample mounted strain-free in superfluid He at ~1.5 K, using a Fourier transform infrared (FTIR) spectrometer and a liquid nitrogen-cooled Ge p-i-n diode detector, and a spectral resolution of 2.5 μ eV (0.02 cm-1).
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