Optimising modulation depth of ultra-low loss phase change chalcogenide Sb2Se3 for silicon photonics platforms

Blundell, Sophie, Muskens, Otto and Zeimpekis, Ioannis (2024) Optimising modulation depth of ultra-low loss phase change chalcogenide Sb2Se3 for silicon photonics platforms. PHOTOPTICS 2024: 12th International Conference on Photonics, Optics and Laser Technology, , Rome, Italy. 21 - 23 Feb 2024.

Abstract

Phase change materials (PCMs) exist in multiple solid states with different refractive indices which can be switched between thermally, electrically or optically. Interest in the antimonides, namely Sb2Se3 and Sb2S3, has increased over the last decade, due to the ultralow loss of such materials [1]. In this work, we propose and investigate a method for increasing modulation depth of Sb2Se3 used within integrated photonic devices as a phase shifter. By increasing the thickness of Sb2Se3 while embedding it deeper into the Si waveguide we see an increased modulation. Varying the capping layer used on PCMs integrated into nanophotonic chips affects crystallisation dynamics, whilst also providing protection from ions being lost during the switching process [2]. It has been shown that rapid thermal annealling applied to dopants in Si increases diffusion of the dopant ions [3]. As such, whilst also using a capping layer of SiO2 in this work, we investigate the benefits of putting a barrier oxide layer between the PCM and Si chip, to prevent diffusion of ions into the Si chip. We present results to support use of a barrier layer between PCM and chip when depositing thinner layers, as this is where the diffusive effect appears to affect modulation efficiency most potently. We will demonstrate this improved modulation contrast when the PCM is embedded into multimode interferometers (MMIs) as a method of changing the splitting ratio between the output couplers, simply by switching specific areas of the PCM. Over a total length of 50µm, Sb2Se3 is incrementally crystallised by 1µm and the MZI spectra taken after each switching event. This gives a wavelength shift in the spectrum, a direct analogy for the phase shift induced by each of these incremental switching events. Wavelength shift is presented against length of PCM crystallised, showing that increasing amount of Sb2Se3 crystallised increases wavelength shift. We investigate this process for five depositions of increasing thickness and etch depth, the gradients of which are then extracted. This gives the difference in wavelength shift imposed by incorporating a barrier oxide layer between PCM and Si waveguide, most noticeable in the thinner depositions. This can be attributed to the greater impact that ion diffusion into the Si waveguide has at smaller thicknesses of Sb2Se3; little difference is seen at greater thicknesses due to the smaller surface area to volume ratio of the Sb2Se3 in this case. [1] Matthew Delaney et al., Advanced Functional Materials 30.36 (Sept. 2020), p. 2002447. [2] Ting Yu Teo et al., ACS Photonics 10 (2023), pp. 3203–3214. [3] R. Angelucci, P. Negrini, and S. Solmi., Applied Physics Letters 49.21 (Nov. 1986), pp. 1468–1470.

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Contributors

Author: Otto Muskens

Author: Ioannis Zeimpekis

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