Phase change of Ge2Sb2Te5 under terahertz laser illumination

Kang Zhou,Ming Yan,Junyi Nan,Hua Li,Jiabin Shen,J C Cao,Min Zhu,Ziping Li,Boqu He,Heping Zeng,Zhitang Song

doi:10.1063/5.0070304

Abstract

Ge2Sb2Te5 (GST) is the typical phase change material (PCM) that can reversibly transform between the amorphous (a) and crystalline (c) states. Because the optical properties are phase-dependent, GST has been widely used in various photonic applications, such as optical switches and non-volatile memories. Currently, the photonic applications of the GST PCM have been demonstrated by employing lasers in visible and infrared wavelengths. Extending the photonic applications into other wavelengths is much demanded. Here, we investigate the phase change of the GST material illuminated by using a terahertz quantum cascade laser emitting around 2.5 THz. A finite-element simulation is employed to study the temperature and transmission changes induced by terahertz irradiation. It reveals that the phase change can be achieved and the transmission is reduced by 30% when the GST material is irradiated by the 2.5 THz laser light. Furthermore, a z-scan technique experimentally presents the phase change behaviors of GST illuminated by the terahertz light, which is visually proved by transmission electron microscopy. Our work paves a way for the applications of GST materials in the terahertz optical components, e.g., modulators and switches.

Highlights

In the last half century, electronic devices have significantly promoted the development of the computing technology following the von Neumann approach.1,2 Currently, the world generates exponentially increasing amounts of data that need to be processed in a fast and efficient way
The transmission measurements for the c-GST sample are used to verify if the amorphous GST (a-GST) samples under terahertz illumination can phase change to the c-GST because the transmission difference between the two samples at 2.5 THz can vary by 30%
It was expected that as the optical power was further increased, the phase change from aGST to c-GST or a transmission decrease could be observed. This abnormal behavior of the GST sample under large optical power illumination can be explained as follows: as can be seen from Fig. 3(b), when the temperature is increased due to higher power illumination (2.5 mW), around the focal point, the a-GST phase is changed to the c-GST and hexagonal GST (h-GST)

Summary

INTRODUCTION

Scitation.org/journal/apm conventional GST-based PCM devices relies on the fast phase change between multilevel states under certain temperature conditions employing an electrical-induced or optical-induced heating, i.e., amorphous GST (a-GST) at room temperature, cubic GST (cGST) at ∼ 150 ○C (423 K), and hexagonal GST (h-GST) at ∼ 300 ○C (573 K).. The rapid development of the light source in the visible and infrared frequencies has boosted the applications of GST materials in data storage, integrated optical switches, and perfect absorbers.. The rapid development of the light source in the visible and infrared frequencies has boosted the applications of GST materials in data storage, integrated optical switches, and perfect absorbers.20 In these frequency regimes, the optical reflectivity of GST increases with increasing annealing temperature induced by higher optical power irradiation.. Investigations of the phase change of GST under terahertz QCL illumination will boost the applications of GST materials and, simultaneously, diversify the application fields of terahertz QCLs. In this work, we investigate the phase change of GST materials in the terahertz frequency range, employing a QCL emitting around 2.5 THz. A z-scan technique is utilized to gradually change the terahertz power density irradiated onto the GST samples and to achieve the phase change. This work diversifies the application fields of terahertz QCLs

Spectral and structural properties of GST films

RESULTS AND DISCUSSION

CONCLUSIONS