Tuesday, 28 July 2015

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


We demonstrate improved terahertz (THz) modulation using thermally crystallized germaniumtelluride (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 weresputtered on sapphire substrates and then tested using THz time-domain spectroscopy (THz-TDS). The test samples, heated  while collecting THz-TDS measurements, 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 monitoring electrical 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 sapphiresubstrate. After isolating the sapphire and the crystalline GeTe (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 GeTe. These results strongly motivate using GeTe or other chalcogenide thin films in THz modulators, filters, and metamaterial applications.


The measurments in this paper were collected with a TeraView THz-TDS spectroscopy system equipped with a variable temperature sample holder.