Improved terahertz modulation using germanium telluride (GeTe) chalcogenide thin films

Jul 20, 2015

A. H. Gwin ; C. H. Kodama ; T. V. Laurvick ; R. A. Coutu Jr. ; P. F. Taday


We demonstrate improved terahertz (THz) modulation using thermally crystallizedgermanium telluride (GeTe) thin films. GeTe is a chalcogenide material that exhibits a nonvolatile, amorphous to crystalline phase change at approximately 200 °C, as well as six orders of magnitude decreased electrical resistivity. In this study, amorphous GeTe thin films were sputtered on sapphire substrates and then tested using THz time-domainspectroscopy (THz-TDS). The test samples, heated in-situ while collecting THz-TDSmeasurements, exhibited a gradual absorbance increase, an abrupt nonvolatile reduction at the transition temperature, followed by another gradual increase in absorbance. The transition temperature was verified by conducting similar thermal tests while monitoringelectrical resistivity. THz transmittance modulation data were investigated between 10 and 110 cm−1 (0.3–3.3 THz). A peak modulation of approximately 99% was achieved at 2.3 THz with a 100 nm GeTe film on a sapphire substrate. After isolating the sapphire and the crystalline GeTe (c-GeTe) absorbance contributions, the results showed THz modulations ranging from 88.5% to 91.5% that were attributed solely to the single layer of transitioned c-GeTe. These results strongly motivate using GeTe or other chalcogenide thin films in THzmodulators, filters, and metamaterial applications.