Suppressed electronic contribution in thermal conductivity of Ge2Sb2Se4Te

Kiumars Aryana,Juejun Hu,Patrick E Hopkins,David H Olson,Eric R Hoglund,John A Tomko,Md Shafkat Bin Hoque,Yifei Zhang,Carlos Ríos,Joyeeta Nag,John C Read

doi:10.1038/s41467-021-27121-x

Abstract

Integrated nanophotonics is an emerging research direction that has attracted great interests for technologies ranging from classical to quantum computing. One of the key-components in the development of nanophotonic circuits is the phase-change unit that undergoes a solid-state phase transformation upon thermal excitation. The quaternary alloy, Ge2Sb2Se4Te, is one of the most promising material candidates for application in photonic circuits due to its broadband transparency and large optical contrast in the infrared spectrum. Here, we investigate the thermal properties of Ge2Sb2Se4Te and show that upon substituting tellurium with selenium, the thermal transport transitions from an electron dominated to a phonon dominated regime. By implementing an ultrafast mid-infrared pump-probe spectroscopy technique that allows for direct monitoring of electronic and vibrational energy carrier lifetimes in these materials, we find that this reduction in thermal conductivity is a result of a drastic change in electronic lifetimes of Ge2Sb2Se4Te, leading to a transition from an electron-dominated to a phonon-dominated thermal transport mechanism upon selenium substitution. In addition to thermal conductivity measurements, we provide an extensive study on the thermophysical properties of Ge2Sb2Se4Te thin films such as thermal boundary conductance, specific heat, and sound speed from room temperature to 400 °C across varying thicknesses.

Highlights

Integrated nanophotonics is an emerging research direction that has attracted great interests for technologies ranging from classical to quantum computing
Understanding the thermal transport properties of phase change materials (PCMs) is of critical importance to design and modeling of active photonic devices based on PCMs
Diffuse rings from an amorphous GSST material are still present in this 150 nm selected area diffraction pattern (Fig. 1d), which could suggest incomplete crystallization or minor damage from sample preparation; similar observations are found in the 20 nm crystalline GSST film

Summary

Introduction

Integrated nanophotonics is an emerging research direction that has attracted great interests for technologies ranging from classical to quantum computing. We report on the thermal conductivity, longitudinal sound speed, and volumetric heat capacity of GSST in amorphous and crystalline phases (see Table 1).

Results

Conclusion