Interstitial Aluminum in Silicon for Quantum Technologies

Defects in silicon are a promising platform for quantum devices due to their compatibility with existing silicon nanophotonics, microelectronics, and commercial foundry processes. We explore the viability of interstitial aluminum (Al_i) in the singly ionized charge state (Al_i⁺) as a single-photon source or spin-photon interface. It is both stable at room temperature and easy to form. The earliest study on Al_i was performed by ESR in 1964 [1] and there has been only one prior study of its optical properties [2]. We perform absorption spectroscopy of Al_i⁺ and identify the first two excited states as a spin triplet (1s:³T₂) and singlet (1s:¹T₂) in contrast with [2]. These states emit within the L and C telecommunication bands suitable for low-loss, long-distance communication. We further investigate the fine structure and spin-orbit coupling within the long-lived 1s:³T₂ state and show that its lifetime exceeds several milliseconds. We conclude by proposing a brokered entanglement scheme with Al_i⁺, mediated by a hyperfine interaction within the metastable state.

[1] G. D. Watkins, “Radiation damage in semiconductors,” Dunod, Paris, 1964

[2] Y. I. Latushko and V. V. Petrov, “IR Studies of Electron-Irradiated Aluminum-Doped Silicon” Defects in Semiconductors (1979) p. 1269