Phase Change Behavior And Infrared Optical Property Of Ge_1-xSn_xTe Under Atmospheric/High Pressure

Typical chalcogenide phase change materials（PCMs）,such as Ge₂Sb₂Te₅ and Ge Te,can rapidly and reversibly transform from amorphous to crystalline states under thermal or electrical excitation,accompanied by dramatic changes in optical properties.This characteristic of PCM has attracted extensive attention from a large number of researchers in the field of optical devices.In addition to the traditional thermal excitation method,pressure as another important thermodynamic parameter,can also stimulate the phase structure change of PCM.Research on PCM in high pressure field was carried out 20 years ago.Up to now,researchers have made important progress in the phase change behavior and electrical properties changes of PCM under high pressure,but there are still some problems.Specifically in the following aspects:（1）PCM is a phase change material with excellent optical properties,but its optical properties under high pressure have not been widely concerned by researchers,especially the infrared optical properties.（2）Lack of comparative analysis of changes in optical properties caused by thermal and pressure-induced phase change.（3）Lack of experimental proof.Most of the existing PCM-based high pressure research is still in the theoretical calculation stage,and the calculation results are often inconsistent and lack experimental proof.For example,the pressure-induced metallization of Ge Te has not been experimentally demonstrated.In response to the above problems,we designed a Ge_1-xSn_xTe phase change material by introducing Sn atoms into Ge Te,and compared it with Ge Te and Ge₂Sb₂Te₅,using a combination of experiments and theoretical calculations to study its phase change and infrared optical property under atmospheric and high pressure.The pressure-induced metallization transitions of Ge_1-xSn_xTe and Ge Te were also verified.The research is mainly divided into the following two parts:（1）The phase change behavior and infrared optical properties of Ge_1-xSn_xTe,Ge Te,Ge₂Sb₂Te₅ under atmospheric pressure.We prepared Ge_1-xSn_xTe,Ge Te,Ge₂Sb₂Te₅films with the same thickness,and found the introduction of Sn makes Ge_1-xSn_xTe have a lower phase change temperature than Ge Te,and Ge_1-xSn_xTe also has the highest infrared reflection modulation ability,followed by Ge Te,and Ge₂Sb₂Te₅ is the worst.Through experimental and theoretical calculations,it is proposed that the high infrared reflection modulation ability of Ge_1-xSn_xTe is derived from the strong p-p coupling due to its highly ordered no-vacancy structure and the high carrier concentration due to its low band gap and low vacancy formation energy.（2）The phase change behavior and infrared optical properties of Ge_1-xSn_xTe and Ge Te under high pressure.The phase structures and infrared reflection of Ge_1-xSn_xTe and Ge Te in the pressure range of 0-30 GPa were characterized,respectively.And the Ge_1-xSn_xTe and Ge Te had the same phase change path（low pressure cubic-high pressure orthorhombic phase）,but the phase change pressure of Ge_1-xSn_xTe is significantly lower than Ge Te.And the infrared reflection modulation ability of Ge_1-xSn_xTe under pressure far exceeds that of Ge Te,even higher than the contrast produced by thermal-induced phase change under atmospheric pressure.By combining the results of experiments and theoretical calculations,it is determined that the metallization transitions of Ge_1-xSn_xTe and Ge Te both occur in the low-pressure cubic phase,and it is pointed out that the high infrared reflection modulation ability of Ge_1-xSn_xTe under high pressure due to the enhancement of electron delocalization caused by its metallization transition.