Abstract
Laser pulses can be utilized to induce intermediate states of phase change materials between amorphous and crystalline phases, making phase change materials attractive and applicable for multi-level storage applications. In this paper, intermediate states of Ge2Sb2Te5 thin films induced via employing a nanosecond multi-pulse laser with different energy and pulse duration were performed by Raman spectroscopy, reflection measurement and thermal simulations. Upon laser-crystallized Ge2Sb2Te5 films, optical functions change drastically, leading to distinguishable reflectivity contrasts of intermediate states between amorphous and crystalline phases due to different crystallinity. The changes in optical intensity for laser-crystallized Ge2Sb2Te5 are also accompanied by micro-structure evolution, since high-energy and longer pulses result in higher-level intermediate states (corresponding to high reflection intensity) and largely contribute to the formation of stronger Raman peaks. By employing thermal analysis, we further demonstrated that the variations of both laser fluence and pulse duration play decisive roles in the degree of crystallinity of Ge2Sb2Te5 films. Laser fluence is mainly responsible for the variations in crystallization temperature, while the varying pulse duration has a great impact on the crystallization time. The present study offers a deeper understanding of the crystallization characteristic of phase change material Ge2Sb2Te5.
Highlights
Accepted: 2 February 2022Chalcogenide phase change materials (PCMs) are a class of materials which can be repeatedly switched between amorphous and crystalline phases, typically by optical or electrical pulses
It was reported that the density of a-Ge2 Sb2 Te5 (GST) film is remarkably increased after crystallization [33], resulting in the slight sinking of the crystallized region compared to the amorphous background
We have investigated the crystallization characteristics of intermediate states in amorphous Ge2 Sb2 Te5 (a-GST) thin films induced by a 532 nm nanosecond multi-pulse laser with different pulse duration and energy
Summary
Chalcogenide phase change materials (PCMs) are a class of materials which can be repeatedly switched between amorphous and crystalline phases, typically by optical or electrical pulses Such materials have significant applications because there are large differences in electrical and optical properties between these phases. PCMs have been widely used in all-photonic memories [1,2,3,4,5,6], color display [7,8], neuro-inspired computing [9], reconfigurable meta-optics [10,11], photonic switches and routers [12,13], and so on Among these PCMs, Ge2 Sb2 Te5 (GST) has received considerable attention in terms of its fast phase switching speed, high optical reflectivity, and outstanding scalability [1,5,14]. The amorphization process can be caused by a short high-power pulse, since it normally requires ultrafast melting and subsequent rapid quenching, whereas a relatively lower-power and longer pulse (namely, a continuous thermal process which above the glass-transition temperature) can result in crystallization
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