Phase Change Materials (GST)

Ge2Sb2Te5 (GST) is a thin film that can switch phases between amorphous and crystalline states due to heating. Around 150C, it switches from an amorphous to a cubic crystal. At 200C it switches to a hexagonal crystal. Reversal is done by raising it to its melting temperature (650C) and the rapidly quenching it. Variants of GST are widely used in optical recording, such as the Bluray DVDs.

One of our applications of GST is tunable color filters. The second application is for optical limiting. Unlike VO2 (which is another phase change material), GST is much easier to fabricate, and can produce large shifts in its optical constants. This has allowed us to design and fabricate multilayer structures employing GST that can switch between a transparent state and a reflective state in response to an incident laser radiation.

We are also studying nano-structured GST (using Glancing Angled Deposition – GLAD) to explore how their switching behavior is altered due to size effects.

XRD measurements on GST films

GST Nanorods grown by Cryogenic Glancing Angle Deposition


    1. Andrew Sarangan, Josh Duran, Vladimir Vasilyev, Nicholaos Limberopoulos, Ilya Vitebskiy, and Igor Anisimov. “Broadband Reflective Optical Limiter Using GST Phase Change Material”. IEEE Photonics Journal, 10(2):1–9, 2018. doi:10.1109/JPHOT.2018.2796448
    2. Pengfei Guo, Joshua A. Burrow, Gary A. Sevison, Aditya Sood, Mehdi Asheghi, Joshua R. Hendrickson, Kenneth E. Goodson, Imad Agha, and Andrew Sarangan, “Improving the performance of Ge2Sb2Te5 materials via nickel doping: Towards RF-compatible phase-change devices”. Appl. Phys. Lett. 113, 171903 (2018); doi:10.1063/1.5053713
    3. Pengfei Guo, Andrew Sarangan, and Imad Agha. “A Review of Germanium-Antimony-Telluride Phase Change Materials for Non-Volatile Memories and Optical Modulators”. Applied Sciences, 9(3):530, 2019. doi:10.3390/app9030530
    4. Gary A. Sevison, Shiva Farzinazar, Joshua A. Burrow, Christopher Perez, Heungdong Kwon, Jaeho Lee, Mehdi Asheghi, Kenneth E. Goodson, Andrew Sarangan, Joshua R. Hendrickson, and Imad Agha. “Phase Change Dynamics and Two-Dimensional 4-Bit Memory in Ge2Sb2Te5 via Telecom-Band Encoding”. ACS Photonics, 2020. doi:10.1021/acsphotonics.9b01456
    5. Pengfei Guo, Joshua A. Burrow, Gary A. Sevison, Heungdong Kwon, Christopher Perez, Joshua R. Hendrickson, Evan M. Smith, Mehdi Asheghi, Kenneth E. Goodson, Imad Agha, and Andrew M. Sarangan. “Tungsten-doped Ge2Sb2Te5 phase change material for high-speed optical switching devices”. Applied Physics Letters, 116(13):131901, 2020. doi:10.1063/1.5142552