A scheme for simulating multi-level phase change photonics materials

Yunzheng Wang,Robert E. Simpson,Michel Bosman,Li Lu,Jing Ning

doi:10.1038/s41524-021-00655-w

Abstract

Chalcogenide phase change materials (PCMs) have been extensively applied in data storage, and they are now being proposed for high resolution displays, holographic displays, reprogrammable photonics, and all-optical neural networks. These wide-ranging applications all exploit the radical property contrast between the PCMs’ different structural phases, extremely fast switching speed, long-term stability, and low energy consumption. Designing PCM photonic devices requires an accurate model to predict the response of the device during phase transitions. Here, we describe an approach that accurately predicts the microstructure and optical response of phase change materials during laser induced heating. The framework couples the Gillespie Cellular Automata approach for modelling phase transitions with effective medium theory and Fresnel equations. The accuracy of the approach is verified by comparing the PCM’s optical response and microstructure evolution with the results of nanosecond laser switching experiments. We anticipate that this approach to simulating the switching response of PCMs will become an important component for designing and simulating programmable photonics devices. The method is particularly important for predicting the multi-level optical response of PCMs, which is important for all-optical neural networks and PCM-programmable perceptrons.

Highlights

Chalcogenide phase change materials (PCMs) exhibit extraordinarily large changes to their optical and electrical properties when switched between their local different bonding states[1,2,3]
Chalcogenide PCMs are attractive for reprogrammable photonics because they exhibit a large optical refractive index change between amorphous and crystalline phases
AgInSbTe and Ge2Sb2Te5 are commonly referred to as growth and nucleation dominated materials, respectively[55]. It is possible for Ge2Sb2Te5 to exhibit a growth-dominated crystallisation behaviour because at high temperature, the growth probability of Ge2Sb2Te5 is much larger than the nucleation probability, meaning that if preexisting nuclei exist in the amorphous background, Ge2Sb2Te5 crystallisation becomes growth dominated

Summary

Introduction

Chalcogenide phase change materials (PCMs) exhibit extraordinarily large changes to their optical and electrical properties when switched between their local different bonding states[1,2,3]. The switching is reversible and can be cycled trillions of times[4] This makes PCMs attractive not just for their existing application in electrical storage[5], and for potential applications in photonics[6,7,8,9], micro-electromechanical systems[10], and tunable radio frequency devices[11]. Chalcogenide PCMs tend to have a larger refractive index in both crystalline and amorphous phases than many other tunable photonics materials, and this makes them naturally suitable for designing all-dielectric metasurfacebased devices[14].

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