Structure Evolution And Infrared Reflective Properties Of Germanium-Tellurium-Based Phase Change Alloys Under Heating/Pressure

As non-volatile materials,chalcogenide phase change materials（PCMs）can be switched rapidly and reversibly between amorphous and crystalline phases with a significant change in optical properties after stimulated by external conditions,and they have attracted the attention of researchers.The structure state of PCMs can be altered under heating/pressure,thereby affecting the optical properties.Germanium-Tellurium-based phase change alloys,as a class of PCMs with excellent comprehensive properties and wide application,have been widely used in optical storage,solid-state display and other fields.So far,the researches on GeTe-based phase change alloys still confront the following problems:First,previous studies have focused mainly on the reflective properties of alloys in the visible and near-infrared bands,whereas the reflective properties of the mid-to-far infrared band,which is an important application band,receive scant attention.Second,GeTe,a heating-induced phase change material with high optical contrast,will possibly achieve higher optical contrast through the introduction of heavy atoms that generate weak chemical bonds.However,no researcher has consciously carried out studies on the optical properties of GeTe-based phase change alloys,and the mechanism of different solute atoms to improve optical properties is still unclear.Third,in the past studies,we have found that GeTe and its solid solution can achieve high optical contrast under pressure,but the mechanism has not been fully accounted for,and the influence of atomic composition on the pressure-induced optical contrast remains unexplored.Aiming at the above problems,this paper introduces solute atoms with different relative atomic masses into GeTe,designs three GeTe-based phase change alloys,and studies their reflective properties in the mid-to-far infrared band.Through the combination of atmospheric/high pressure experiments,spectral fitting and first-principles calculations,we reveal the mechanism of the influence of solute atoms on the infrared reflective properties at atmospheric pressure and high pressure.Based on the previous research on the optical contrast of heating-induced PCMs,this paper proves that pressure can be used as a new way to generate high optical contrast,and this optical contrast can be further improved by introducing suitable solute atoms.This provides an effective reference for promoting the application of PCMs in devices such as all-optical storage and multi-level optical switching.The research content of this paper has important academic value in promoting the research on interdisciplinary issues between materials and high-pressure science,and mainly includes the following two parts:1.Ge_0.9Sb_0.1Te,Ge_0.9Sn_0.1Te and GeSe_0.1Te_0.9alloys with high optical contrast are obtained with the introduction of different solute atoms into GeTe.Under heating,GeTe-based phase change alloys transform from amorphous to crystalline,increasing their reflectivity in the infrared band in the meantime.Through exploring into the relationship between the microstructure and reflective properties,we reveals that a high carrier concentration helps to enhance the infrared reflectivity.In addition,the introduction of heavy atoms is conducive to the formation of weak chemical bonds such as Sb-Te,which in turn improves the reflectivity contrast.This study is beneficial to reveal the mechanism of solute atoms’improvement in the optical properties,and provides a new idea for the design of high optical contrast.2.The infrared reflectivity of cubic GeTe-based phase change alloys can be continuously tuned by applying high pressure to change the interatomic interactions.The structure of all GeTe-based phase change alloys exhibits similar evolution behaviors under pressure.As the pressure increases,the cubic GeTe-based phase change alloys change from a low reflective state to a high reflective state.This is a result of the joint effect of Peierls distortion and vacancy formation energy.This study is of great significance for revealing the mechanism of the influence of atomic composition on the high-pressure optical properties,and provides a new regulation method that improves the optical properties of PCMs.