Er Implantation in Silicon Enables Scalable Memory, with Five Centers Formed at 1018cm-3 and Quench Rates to 400 degC/s

Erbium-implanted silicon presents a compelling pathway towards scalable planar memory technologies, but controlling the formation of erbium centres within the silicon lattice remains a significant challenge. Mark A. Hughes from the University of Salford, alongside Huan Liu and Yaping Dan from Shanghai Jiao Tong University, investigated how quickly cooling the material after erbium implantation affects the types of erbium centres that develop. The team systematically varied the cooling rate following implantation and then tracked the resulting changes in the material’s optical properties, revealing the presence of five distinct erbium centres. Crucially, they discovered that faster cooling suppresses one type of centre, favouring the formation of a silicon-coordinated erbium centre, a key requirement for achieving reliable and efficient quantum memory devices. This research demonstrates a powerful method for selectively engineering the composition of erbium-implanted silicon, paving the way for improved performance in future memory applications.

Researchers correlated observed photoluminescence spectra with the crystal field parameters of the erbium centers, employing simulations and experimental measurements to achieve this. Simulations reveal how implant energy influences the distribution of erbium ions within the silicon substrate, and demonstrate the recoil of oxygen atoms from the silicon dioxide layer into the silicon substrate during implantation, highlighting the role of defects. Experimental data shows the temperature decay during rapid cooling for different samples, demonstrating the achieved cooling rates.

Erbium Centre Formation via Quench Annealing

This research pioneered a precise methodology for controlling the formation of erbium centers within silicon, crucial for developing scalable planar memory. Scientists implanted erbium into phosphorus-doped silicon wafers, controlling the ion distribution to a depth of approximately 1. 5μm to achieve a uniform concentration of 1018cm-3. Following implantation, samples underwent annealing using both conventional rapid thermal annealing and a novel rapid quench annealing technique performed within a modified dilatometer under high vacuum. Samples were initially cooled from 950°C to 25°C at varying, precisely controlled rates before being rapidly cooled to -100°C at a consistent rate, allowing scientists to systematically investigate the relationship between cooling rate and the formation of distinct erbium centers.

Optical measurements, performed using a closed-cycle helium cryostat reaching 3. 5 K, excited fluorescence with a 520nm laser, dispersed using a monochromator, and detected with an infrared-sensitive photomultiplier tube. The resulting photoluminescence spectra were corrected for system response and analyzed to identify and characterize the different erbium centers present in each sample, and transient fluorescence measurements captured with a 500MHz oscilloscope provided insights into their dynamic behavior. Detailed crystal field analysis, based on the splitting of energy manifolds within the erbium ions, extracted precise crystal field parameters, revealing the local environment surrounding each center and confirming their structural characteristics. This comprehensive approach demonstrated that rapid quench annealing can selectively stabilize a single, silicon-coordinated erbium center, a key requirement for high-performance quantum memory applications, delivering a pathway towards creating scalable and efficient quantum memories for future quantum computing architectures.

Erbium Centers Controlled in Silicon for Quantum Memory

Scientists achieved precise control over the formation of erbium centers within silicon, a crucial step towards scalable quantum memory applications. The research focused on erbium-implanted silicon, utilizing a rapid quench annealing technique to manipulate the characteristics of erbium centers formed after implantation. Experiments involved implanting silicon with a concentration of 1018cm-3 of erbium and then subjecting the samples to rapid thermal processing with cooling rates varying from 5 to 400°C/s. Detailed analysis of photoluminescence revealed the presence of five distinct erbium centers, each with unique properties.

Two of these centers, one coordinating with both silicon and oxygen and the other with silicon alone, exhibited fully resolved crystal-field splitting of the 4I15/2 ground state, alongside 2 to 3 hot lines from the 4I13/2 excited state. The team discovered that the erbium center coordinating with both silicon and oxygen was suppressed at cooling rates exceeding 185°C/s, while the silicon-only coordinated center was progressively enhanced with increasing cooling rate, reaching a maximum at 400°C/s. These results demonstrate that rapid quenching can selectively stabilize a single, silicon-coordinated erbium center, a key requirement for efficient quantum memory. The ability to control the formation of these centers opens new avenues for developing planar quantum devices and integrating them with existing silicon photonic technology, delivering a pathway towards creating scalable and efficient quantum memories for future quantum computing architectures.