Resolving Jahn-Teller induced vibronic fine structure of silicon vacancy quantum emission in silicon carbide

Abstract

Point defects in semiconductors are promising single-photon emitters (SPEs) for quantum computing, communication and sensing applications. However, factors such as emission brightness, purity and indistinguishability are limited by interactions between localized defect states and the surrounding environment. Therefore, it is important to map the full emission spectrum from each SPE, to understand the complex interplay between the different defect configurations, their surroundings and external perturbations. Herein, we investigate a family of regularly spaced sharp luminescence peaks appearing in the near-infrared portion of photoluminescence (PL) spectra from n-type 4H-SiC samples after irradiation. This periodic emitter family, labeled the L-lines, is only observed when the zero-phonon line signatures of the negatively charged Si vacancy (so-called V-lines) are present. The L-lines appear with 1.45 meV and 1.59 meV energy spacing after H and He irradiation and increase linearly in intensity with fluence -reminiscent of the intrinsic defect trend. Furthermore, we monitor the dependence of the L-line emission energy and intensity on heat treatments, electric field strength and PL collection temperature, discussing these data in the context of the L-lines. Based on the strong similarity between the irradiation, electric field and thermal responses of the L-and V-lines, the L-lines are attributed to the Si vacancy in 4H-SiC. The regular and periodic appearance of the L-lines provides strong arguments for a vibronic origin explaining the oscillatory multi-peak spectrum. To account for the small energy separation of the L-lines, we propose a model based on rotations of distortion surrounding the Si vacancy driven by a dynamic Jahn-Teller effect.

Exhaustive characterization of Si vacancy complex in 4H-SiC

“…The most prominent line is around 1.412 eV (878 nm). This line is also found in connection to measurements done for the L-lines-additional lines that span a 15 meV range next to the h silicon vacancy and are tentatively suggested to be vibronic replicas of the silicon vacancy [24]. Before assigning the above signals to a novel defect, it is necessary to consider the role of other perturbative effects such as thermal vibration, strain, and surface termination.…”

“…Within the 15 meV range next to the isolated h silicon vacancy, we observe a set of lines in the same region as L-lines [24], see Figure 6a. However, there is no one-to-one correspondence due to disagreement in the observed intensities and energy spacing from earlier study [24]. The L-lines are tentatively suggested to be vibronic replicas of the silicon vacancy [24].…”

“…However, there is no one-to-one correspondence due to disagreement in the observed intensities and energy spacing from earlier study [24]. The L-lines are tentatively suggested to be vibronic replicas of the silicon vacancy [24]. However, the L-lines disappear upon annealing at 800 K, whereas the silicon vacancy remains [24] which contradicts this hypothesis.…”

“…The L-lines are tentatively suggested to be vibronic replicas of the silicon vacancy [24]. However, the L-lines disappear upon annealing at 800 K, whereas the silicon vacancy remains [24] which contradicts this hypothesis. Alternatively, these lines could originate from strain, surface effects, or another defect.…”

“…Many of the predicted ZPLs from the modified vacancies fall close to the isolated value. This makes it difficult to exclude other effects like strain [27], L-lines [24] or surface effects. Hence, we focus on the lines farthest away from silicon vacancy, at least 15 meV from the isolated line.…”