硫族化合物相變材料（PCMs）能夠在結晶相和非晶相之間迅速、可逆地轉換。兩相之間原子結構和鍵合機制的巨大差異導致兩相在電學和光學性質方面存在顯著不同，可用于數字數據的編碼。

近年來，一種基于PCMs的新型非易失性電子存儲器已被開發出來并實現商業化，在開關速度、存儲容量和可擴展性方面具有優異的器件性能。隨著硅波導平臺的快速發展，基于PCMs的光學和光子器件由于能夠超越衍射極限并應用于高密度集成而再次回歸人們的視線。

摻雜的Sb₂Te合金由于其生長驅動的結晶特性，在芯片級光子應用中受到了越來越多的關注。然而，目前尚不清楚Sb₂Te在器件中納秒級結晶時是否也會形成與成核驅動的Ge-Sb-Te合金類似的亞穩態結晶相。

Fig. 3 Dielectric function.

來自西安交通大學材料創新設計研究中心的張偉教授團隊，對Sb₂Te材料進行了多尺度模擬，包括基于密度泛函理論的從頭算分子動力學計算以及有限差分時域模擬，以揭示Sb₂Te在超快結晶和后續熱退火過程中結構和光學性質的演化。

他們發現，超快結晶后得到的Sb₂Te晶體是無序的A7結構，碲原子隨機分布在體內。進一步退火將導致Te的有序化過程，并逐漸轉變為完全有序的結構，所有Te原子在Sb₂Te₃中形成完美的層。

Fig. 5 Electronic structure of random-swap models.

快速結晶和退火后之間的結構差異導致了電子結構的不同，從而導致了光學性質隨波長的依賴關系發生變化，即在電信波段有顯著的影響，而對可見光區域的影響可以忽略不計。

Fig. 6 Relationship between atomic structure and electronic structure.

作者的工作展示了對材料的原子級理解將如何指導器件設計，并有望促進未來對Sb₂Te基合金在各種光子相變應用中的探索。該文近期發布于npj Computational Materials 9: 136 (2023).

Editorial Summary

Chalcogenide phase change materials (PCMs) can rapidly and reversibly switch between crystalline and amorphous phases. The large difference in atomic structure and bonding mechanism between the two phases gives rise to a notable contrast in electrical and optical properties, which can be used to encode digital data. In the recent decade, an emerging type of non-volatile electronic memory utilizing PCMs has been developed and commercialized with superior device performance in switching speed, storage capacity and scalability. Thanks to the fast development of silicon waveguide platforms, PCM-based optical and photonic devices are gaining renewed attention, since they can go beyond the diffraction limit for high-density integration. Doped Sb₂Te alloys are now gaining increasing attention for on-chip photonic applications, due to their growth-driven crystallization features. However, it remains unknown whether Sb₂Te also forms a metastable crystalline phase upon nanoseconds crystallization in devices, similar to the case of nucleation-driven Ge-Sb-Te alloys.

A?group led by Prof. Wei Zhang from the Center for Alloy Innovation and Design, Xi’an Jiaotong University, carried out multiscale simulations on Sb₂Te, including density functional theory based ab initio molecular dynamics calculations and finite-difference time-domain simulations, to unveil the structural and optical evolution of Sb₂Te during ultrafast crystallization and subsequent thermal annealing. They found that the atomic structure of crystalline Sb₂Te obtained after ultrafast crystallization is a disordered A7 structure with Te atoms randomly distributed in the bulk. The crystallized structure can be further annealed to induce a tellurium ordering process, and gradually transformed to a fully ordered structure with all the Te atoms forming perfect layers in the Sb₂Te₃blocks. The structural difference between the rapidly crystallized and post annealed structures leads to a difference in electronic structure and thereby wavelength-dependent variations of the optical properties, i.e., it has notable influence in the telecom region, but negligible influence in the visible light region. This work showcases how atomic understanding of materials can guide device design, and is expected to stimulate future exploration of Sb₂Te-based alloys for various photonic phase-change applications.?This article was recently published in npj Computational Materials 9: 136 (2023).

原文Abstract及其翻譯

Multiscale simulations of growth-dominated Sb₂Te phase-change material for non-volatile photonic applications?(應用于非易失性光子器件的生長型Sb₂Te相變材料的多尺度模擬)

Xu-Dong Wang,Wen Zhou,?Hangming Zhang,?Shehzad Ahmed,?Tiankuo Huang,?Riccardo Mazzarello,?En Ma?&?Wei Zhang?

Abstract Chalcogenide phase-change materials (PCMs) are widely applied in electronic and photonic applications, such as non-volatile memory and neuro-inspired computing. Doped Sb₂Te alloys are now gaining increasing attention for on-chip photonic applications, due to their growth-driven crystallization features. However, it remains unknown whether Sb₂Te also forms a metastable crystalline phase upon nanoseconds crystallization in devices, similar to the case of nucleation-driven Ge-Sb-Te alloys. Here, we carry out ab initio simulations to understand the changes in optical properties of amorphous Sb₂Te upon crystallization and post annealing. During the continuous transformation process, changes in the dielectric function are highly wavelength-dependent from the visible-light range towards the telecommunication band. Our finite-difference time-domain simulations based on the ab initio input reveal key differences in device output for color display and photonic memory applications upon tellurium ordering. Our work serves as an example of how multiscale simulations of materials can guide practical photonic phase-change applications.

摘要硫族化合物相變材料（PCMs）已被廣泛應用于非易失性存儲器和類腦計算等電子和光子器件中。摻雜的Sb₂Te合金由于其生長驅動的結晶特性，在芯片級光子應用中受到了越來越多的關注。然而，目前尚不清楚Sb₂Te在器件中納秒級結晶時是否也會形成與成核驅動的Ge-Sb-Te合金類似的亞穩態結晶相。本文中，我們開展了從頭算模擬，以理解非晶態Sb₂Te在結晶和退火后光學性質的變化。在這一連續變化過程中，介電函數的變化從可見光范圍到電信波段與波長高度相關。基于從頭算輸入的有限差分時域模擬，揭示了在碲有序化之后，彩色顯示器和光子存儲器等器件輸出的關鍵差異。本工作可作為材料多尺度模擬指導實際光子相變應用的實例。