Off-resonant photoluminescence spectroscopy of high-optical quality single photon emitters in GaN (2501.05546v2)

Abstract: In this work, we analyze the relevance of excitation parameters on the emission from single-photon emitting defect centers in GaN. We investigate the absorption spectrum of different emitters by photoluminescence excitation technique at 10\,K. We report large spectral jumps (shifts up to 22\,meV) in the emitters' zero-phonon line (ZPL). The likelihood of such jumps is increased by the change in excitation energy. The shifts indicate a large built-in dipole moment of the defects and suggest a possibility to electrically tune their ZPL in a wide range. From the photoluminescence excitation studies, we observe that for majority of the emitters the absorption peaks exist between 2 and 2.55\,eV. The absorption peaks vary from emitter to emitter, and no universal absorption pattern is apparent. Finally, for selected emitters we observe significantly reduced spectral diffusion and instrument-limited linewidth of $138\,\mu eV$ (0.04\,nm).These findings show a new perspective for atomic defect GaN emitters as sources of coherent photons, shine new light on their energy level structure and show the possibility of tuning the ZPL, paving the way to fully harness their potential for applications in quantum technologies.

• The paper demonstrates that off-resonant photoluminescence spectroscopy reveals single-photon emitters in GaN with a linewidth limited to 138 μeV, indicating minimal spectral diffusion.
• It employs a confocal microscopy setup at 10 K with a 2.33 eV laser to uncover variable absorption peaks and spectral jumps of up to 22 meV among defect centers.
• The results highlight a significant built-in dipole moment in GaN defects, offering promising avenues for electrical tuning in quantum communication and photonic devices.

Off-Resonant Photoluminescence Spectroscopy of High-Optical Quality Single Photon Emitters in GaN

The paper by Dalla et al. explores the intricate photoluminescence characteristics of defect centers in Gallium Nitride (GaN), which have emerged as promising candidates for single-photon emitters, crucial in quantum technology applications. The research focuses on the impact of excitation parameters on emission properties, revealing significant insights into the atomic-level dynamics and tunability of these defects.

Experimental Approach

The authors employed a variety of spectroscopic techniques to analyze the behavior of single-photon emitters within GaN, specifically utilizing photoluminescence excitation spectroscopy at cryogenic temperatures (10 K). This involved using a homemade confocal microscopy setup with a 2.33 eV laser, allowing for high-resolution spatial mapping and spectral analysis. The GaN samples, grown using MOCVD on sapphire substrates, were characterized by a high concentration of optically active defects, with a density estimated at approximately $0.01-0.1 \, \text{emitters}/\mu m^2$.

Key Findings

1. Spectral Diffusion and Linewidth: A notable achievement of this paper was the observation of emitters with an exceptionally narrow linewidth, measuring at the spectrometer resolution limit of 138 $\mu eV$. This indicates minimal spectral diffusion, a critical factor for applications requiring photon indistinguishability. The reduction in spectral diffusion was attributed to the high-quality crystallinity of the sample.
2. Photoluminescence Excitation (PLE) Studies: The research identified varying absorption peaks for different emitters, predominantly located between 2 and 2.55 eV. The absence of a consistent absorption pattern across emitters emphasizes the variability in local defect environments and their electronic structures.
3. Spectral Jumps: The single-photon emitters exhibited significant spectral jumps in their zero-phonon lines (ZPLs), with shifts up to 22 meV. These shifts were non-deterministic but correlated with changes in excitation energy, suggesting a robust intrinsic dipole moment.
4. Built-in Dipole Moment: The substantial spectral shifts imply a large built-in dipole moment, indicating potential avenues for electrical tuning of these emission lines. This phenomenon signifies a pivotal property for tuning and modulating photon emissions for quantum communication and information processing applications.

Implications and Future Work

The findings from this research provide a framework for further exploration into the atomic defects in GaN, underscoring their role as viable sources of coherent photons. The ability to manipulate the ZPL through electrical means, as suggested by the observed dipole moments, could revolutionize quantum technologies by offering a new dimension of control in photonic devices.

Future investigations could expand on this paper by exploring different growth conditions and dopant levels to understand and optimize the defect formation and emission properties further. Moreover, characterizing the actual lifetime of these defect states and their interaction with phonons can elucidate mechanisms to mitigate spectral diffusion, enhancing photon indistinguishability.

In summary, the paper enhances our understanding of defect-based single-photon emitters in GaN and paves the way for their integration into quantum technologies, with potential applications in telecommunications, secure communications, and on-chip quantum photonics. Such insights are fundamental for advancing the design and engineering of quantum materials with tailored photonic properties.