Laser writing and spin control of near infrared emitters in silicon carbide

TL;DR

This work addresses the challenge of creating telecom-band emitters and spin qubits in 4H-SiC with scalable fabrication. It demonstrates that direct femtosecond laser writing followed by thermal annealing can produce a bright near-telecom $O$-band emission, likely from the ensemble $N_{C} V_{Si}^-$ centers, while low-energy writes generate a few divacancies (PL5/PL6) that support optical spin read-out and coherent manipulation at room temperature. ODMR, Rabi, Ramsey and Hahn-Echo experiments show that spin coherence is preserved after laser fabrication, with $T_2$ times reaching sub-microsecond to microsecond scales depending on defect and conditions. Overall, the results establish a maskless, depth-controlled approach to integrate spin-photon qubits in SiC, compatible with photonic nanostructures and telecom networking for quantum communication and sensing.

Abstract

Near infrared emission in silicon carbide is relevant for quantum technology specifically single photon emission and spin qubits for integrated quantum photonics, quantum communication and quantum sensing. In this paper we study the fluorescence emission of direct femtosecond laser written array of color centres in silicon carbide followed by thermal annealing. We show that in high energy laser writing pulses regions a near telecom O-band ensemble fluorescence emission is observed after thermal annealing and it is tentatively attributed to the nitrogen vacancy centre in silicon carbide. Further in the low energy laser irradiation spots after annealing, we fabricated few divacancy, PL5 and PL6 types and demonstrate their optical spin read-out, and coherent spin manipulation (Rabi and Ramsey oscillations and spin echo). We show that direct laser writing and thermal annealing can yield bright near telecom emission and preserve the spin coherence time of divacancy at room temperature.

Figures (5)

• Figure 1: (a) RT confocal map of after-annealing laser written array using a 976 nm excitation and 210 $\mu$W optical power. The laser energy per pulse inscription is superimposed. (b) Average photon count rate for 210 $\mu$W optical power after long pass filter at 1000 nm versus the laser writing energy. The lowest energy detected is corresponding to dots written at 22 nJ/pulse due to high background counts in the non-irradiated area of 5500 cts/s.
• Figure 2: (a) Low temperature confocal map of after-annealing laser written array using a 976 nm excitation and 3 mW optical power. (b) Comparison of the 5.5 K PL of a laser written dot at 225 nJ/pulse excited at 3 mW (blue line) compared to a 5 mW 976 nm excitation of a H$^{+}$ irradiated sample at fluence of 10$^{16}$ cm$^{-2}$, fabricated in the same material as per ref. CastellettoDeterministic2019 after 900 $^\circ$ C annealing (gray line). The ensemble of the $\rm N_{C} V_{Si}^{-}$ was created, where some of the ZPLs are shown. (c) Temperature dependent PL of a 180 nJ/pulse laser written dot excited with 210 $\mu$W optical power, showing a moderate temperature dependence and a PL reduction at lower temperature. (d) Low temperature PL of various laser written dots with energy 225, 180, 157, 67, 34, 13 nJ/pulse excited with 976 nm 3 mW optical power.
• Figure 3: (a) RT confocal map of laser written array at 2 $\mu$m using a 800 nm pulsed excitation and 0.5 mW optical power. (b) Exemplary PL time trace for a 445 nJ/pulse and 22 nJ/pulse laser written dots at 4 $\mu$m. (c-d) Lifetime dependence ($\tau_1$ and $\tau_2$ shorter and longer components) versus laser fabrication energy at the two depths.
• Figure 4: (a) $60\times 60~\mu$m$^2$ RT confocal map of laser written array at 4 $\mu$m using a 914 nm CW excitation at 0.2 mW and SNSPD to measure lower energy irradiation from 2 nJ/pulse to 22 nJ/pulse. The circle at 4.5 nJ/pulse indicates a PL5 divacancy identified by the subsequent spin control. (b-c) RT ODMR of the PL5 showing high contrast of 12% and two branches (Right and left). (d-e-f) Rabi oscillation, Ramsey decay and Hahn-Echo of the PL5's left ODMR branch with related T$_2^{*}$ and T$_2$ measurements.
• Figure 5: (a) $60\times 60~\mu$m$^2$ RT confocal map of laser written array at 2 $\mu$m using a 914 nm CW excitation at 0.2 mW and SNSPD to measure lower energy irradiation from 2 nJ/pulse to 22 nJ/pulse. The circle at 4.5 nJ/pulse indicates a PL6 divacancy identified by the subsequent spin control. (b-c) RT ODMR of the PL6 showing high contrast of 7% and two branches (Right and left). (d,e,f) Rabi oscillation, Ramsey decay and Hahn-Echo of the PL6's left ODMR branch with related T$_2^{*}$ and T$_2$ measurements.