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Journal of the Optical Society of America B

Quench rate dependence of the center formation in Er-implanted Si

Mark Hughes, Huan Liu, Yaping Dan

Published Jan 13, 2026• 0 citations
Publisher

Abstract

Er-implanted Si (Er:Si) is a promising candidate for scalable planar quantum memory (QM) applications. In Er:Si, Er has a preference to coordinate with O impurities, and multiple types of Er center are typically formed after a post-implant anneal. Intrinsic Si was implanted with 10 18 cm −3 Er, then annealed using a rapid quench annealing technique at 950°C for 10 min with quench rates of 5°C, 23°C, 46°C, 93°C, 185°C, and 400°C/s. The evolution of photoluminescence (PL) peaks and their associated Er centers was tracked as a function of quench rate. Across all samples, five distinct Er centers were identified. Two centers, one with mixed Si/O coordination and one with Si-only coordination, exhibited fully resolved crystal-field splitting of the 4 I 15/2 ground state together with 2–3 hot lines from the 4 I 13/2 excited state; fitting crystal-field parameters for both was consistent with C 2v symmetry. The mixed Si/O coordinated center was suppressed at quench rates above 185°C/s, while the Si-only coordinated center was progressively enhanced with increasing quench rate up to the maximum of 400°C/s. These results indicate that rapid quench annealing can favor the formation of Si-coordinated Er centers in Er:Si, which is required for QM applications.

DOI
10.1364/josab.582175

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Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures thus making them a promising candidate for optical quantum memories [1], optical-microwave transducers [2] and single dopant-based devices such as single photon emitters operating at the telecommunication wavelengths [3]. Here, we present an overview of the spin and optical properties of Er ensembles in Si accessed via resonant photoluminescence excitation (PLE) spectroscopy [4]. Samples were positioned directly on top of tailor-fabricated superconducting single photon detectors, placed in a dilution refrigerator unit and resonantly excited using fiber optics. Our method provided high collection efficiency and allowed spectral measurements of low Er density samples. The observed Er PLE spectra were strongly affected by the presence of co-dopants such as O, B or P reflecting their influence on the formation of optically active Er sites and corresponding Er optical transition energies. Higher O densities resulted in especially rich PLE spectra suggesting that a variety of Er-O complexes formed due to O doping. Lowering the O concentration, we achieved PLE spectra dominated by a single Er site in P doped samples. Interestingly, the Er spin relaxation and optical coherence properties were barely affected by the employed co-dopants and mainly depended on the Er concentration. By lowering the Er concentration from relatively high (1018cm-3) to low densities (1016cm-3), we were able to increase Er spin lifetimes from ~0.1 s to ~30 s. Long spin relaxation times allowed us to identify PLE spectra of new Er sites in Si. In both concentration regimes, we observed sub-MHz transient spectral holes suggesting long optical coherence times. Furthermore, we observed sub-MHz spin transitions in both natural and isotopically purified Si and achieved spin coherence times above 1 ms in isotopically purified Si. Narrow optical linewidths and long transverse and longitudinal spin relaxation times show that Er in Si is an excellent candidate for future quantum information and communication applications.

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Er-implanted Si (Er:Si) is a promising candidate for scalable planar quantum memory (QM) applications. In Er:Si, Er has a preference to coordinate with O impurities, and multiple types of Er center are typically formed after a post-implant anneal. Intrinsic Si was implanted with 10 18 cm −3 Er, then annealed using a rapid quench annealing technique at 950°C for 10 min with quench rates of 5°C, 23°C, 46°C, 93°C, 185°C, and 400°C/s. The evolution of photoluminescence (PL) peaks and their associated Er centers was tracked as a function of quench rate. Across all samples, five distinct Er centers were identified. Two centers, one with mixed Si/O coordination and one with Si-only coordination, exhibited fully resolved crystal-field splitting of the 4 I 15/2 ground state together with 2–3 hot lines from the 4 I 13/2 excited state; fitting crystal-field parameters for both was consistent with C 2v symmetry. The mixed Si/O coordinated center was suppressed at quench rates above 185°C/s, while the Si-only coordinated center was progressively enhanced with increasing quench rate up to the maximum of 400°C/s. These results indicate that rapid quench annealing can favor the formation of Si-coordinated Er centers in Er:Si, which is required for QM applications.
Er implanted Si (Er:Si) is a promising candidate for scalable planar quantum memory (QM) applications. Er has a preference to coordinate with O impurities, and multiple types of Er center are typically formed after a post implant anneal. Float zone Si was implanted with 1018 cm-3 Er and separate samples were annealed using a rapid quench annealing technique at 950 degC for 10 min with quench rates of 5, 23, 46, 93, 185 and 400 degC/s. The evolution of photoluminescence (PL) peaks and their associated Er centers was tracked as a function of quench rate. Across all samples, five distinct Er centers were identified. Two centers, one with mixed Si and O coordination and one with Si-only coordination, exhibited fully resolved crystal-field splitting of the 4I15/2 ground state together with 2 to 3 hot lines from the 4I13/2 excited state; fitting of crystal-field parameters for both was consistent with C2v symmetry. The mixed Si and O coordinated center was suppressed at quench rates above 185 degC/s, while the Si-only coordinated center was progressively enhanced with increasing quench rate up to the maximum of 400 degC/s. These results demonstrate that rapid quench annealing has the potential to selectively stabilize a single, Si-coordinated Er center in Er:Si, which is required for QM applications.
Erbium implanted silicon (Er:Si) is a promising platform for quantum networking applications, but a major obstacle is the formation of multiple Er centres. We show that the previously identified cubic centre (Er-C) has C2v or lower symmetry. Using crystal field analysis of Er-C and other Er centres, and by comparison with extended X-ray absorption fine structure (EXAFS) measurements, we show that Er centres can be arranged in a sequence, ranging from entirely Si coordinated, through mixed Si and oxygen (O) coordination, to entirely O coordinated. G-factors calculated from our crystal field fitting closely match those determined by Zeeman splitting and electron paramagnetic resonance (EPR) measurements. We co-implanted Si with Er and O (each to a concentration of 1019 cm-3). By increasing the quenching rate of the subsequent thermal anneal from ~100 °C/s to ~1000 °C/s, we change the dominant optically active centre, formed from Er2O3 clusters to the less energetically favourable Er-C centre with mixed Si and O coordination. Temperature dependent photoluminescence (PL) shows that Er2O3 clusters and Er-C centres have an O-related defect state at ~200 and 90 meV above the 4I13/2 Er manifold, respectively. PL lifetime measurements show that the Er2O3 clusters and Er-C centres fall into two or three classes, characterised by different non-radiative PL decay rates. Our high quench rate annealing process could facilitate the formation of a single, optically active Er centre, which is preferable for quantum networking applications of Er:Si.
Erbium-implanted silicon (Er) holds promise for quantum networking, but the formation of multiple Er centres poses a challenge. We show that the cubic centre (Er-C) has C2v or lower symmetry, with Er centres ranging from fully Si- to fully O-coordinated. By co-implanting Si with Er and O (each at 1019 cm-3) and increasing the thermal anneal quenching rate from ~100 °C/s to ~1000 °C/s, we shifted the dominant optically active centre from Er2O3 clusters to the less stable Er-C centre with mixed Si and O coordination. Temperature-dependent photoluminescence reveals Er2O3 clusters and Er-C centres have O-related defect states at ~200 and 90 meV above the 4I13/2 Er manifold, respectively.
Abstract Er implanted Si is a candidate for quantum and photonic applications; however, several different Er centres are generated, and their symmetry, energy level structure, magnetic and optical properties, and mutual interactions have been poorly understood, which has been a major barrier to the development of these applications. Optically modulated magnetic resonance (OMMR) gives a spectrum of the modulation of an electron paramagnetic resonance (EPR) signal by a tuneable optical field. Our OMMR spectrum of Er implanted Si agrees with three independent measurements, showing that we have made the first measurement of the crystal field splitting of the 4I13/2 manifold of Er implanted Si, and allows us to revise the crystal field splitting of the 4I15/2 manifold. This splitting originates from a photoluminescence (PL) active O coordinated Er centre with orthorhombic C2v symmetry, which neighbours an EPR active O coordinated Er centre with monoclinic C1h symmetry. This pair of centres could form the basis of a controlled NOT (CNOT) gate.
Erbium implanted silicon as a quantum technology platform has both telecommunications and integrated circuit (IC) processing compatibility. The electron spin coherence time of Er implanted Si with an Er concentration of 3X1017 cm-3 is measured to be ~10 μs at 5 K and the spin echo decay profile displays strong modulation due to super-hyperfine interaction with 29Si nuclei. Three independent measurements: temperature quenching of photoluminescence (PL), PL lifetime and photo-illuminated electron spin resonance (ESR) all indicate the presence of a previously unreported Er related defect state which can facilitate non-radiative relaxation from the Er exited state. This gives an energy level scheme analogous to that of the diamond NV centre, and implies that optical spin polarisation of the Zeeman ground state and high temperature operation of Er qubits in Er implanted Si may be feasible. The collective coupling strength between a superconducting NbN lumped-element microresonator and Er implanted Si with an Er concentration of 1017 cm-3 at 20 mK was ~ 1 MHz.
Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures thus making them a promising candidate for optical quantum memories [1], optical-microwave transducers [2] and single dopant-based devices such as single photon emitters operating at the telecommunication wavelengths [3]. Here, we present an overview of the spin and optical properties of Er ensembles in Si accessed via resonant photoluminescence excitation (PLE) spectroscopy [4]. Samples were positioned directly on top of tailor-fabricated superconducting single photon detectors, placed in a dilution refrigerator unit and resonantly excited using fiber optics. Our method provided high collection efficiency and allowed spectral measurements of low Er density samples. The observed Er PLE spectra were strongly affected by the presence of co-dopants such as O, B or P reflecting their influence on the formation of optically active Er sites and corresponding Er optical transition energies. Higher O densities resulted in especially rich PLE spectra suggesting that a variety of Er-O complexes formed due to O doping. Lowering the O concentration, we achieved PLE spectra dominated by a single Er site in P doped samples. Interestingly, the Er spin relaxation and optical coherence properties were barely affected by the employed co-dopants and mainly depended on the Er concentration. By lowering the Er concentration from relatively high (1018cm-3) to low densities (1016cm-3), we were able to increase Er spin lifetimes from ~0.1 s to ~30 s. Long spin relaxation times allowed us to identify PLE spectra of new Er sites in Si. In both concentration regimes, we observed sub-MHz transient spectral holes suggesting long optical coherence times. Furthermore, we observed sub-MHz spin transitions in both natural and isotopically purified Si and achieved spin coherence times above 1 ms in isotopically purified Si. Narrow optical linewidths and long transverse and longitudinal spin relaxation times show that Er in Si is an excellent candidate for future quantum information and communication applications.