Amorphous germanium for photonic applications Featured

    AIM Photonics Academy summer intern Ryan Kosciolek creates thin film samples and analyzes their optical, electrical, and material properties.

    Active photonic devices, such as waveguides, can be used in lasers, modulators and sensors. AIM Photonics Academy summer intern Ryan Kosciolek is working under Dr. Anuradha Agarwal, MIT principal research scientist, to deposit thin films of amorphous germanium onto silicon to develop lower cost materials for these applications.

    “I am working on depositing amorphous germanium on various substrates and characterizing the optical, electrical, and material properties to evaluate its use for photonic applications,” Kosciolek, a rising senior at Rutgers University, explains.

    Kosciolek’s work in the lab is supervised by Peter Su, an MIT graduate student in materials science and engineering. “Germanium is a silicon-CMOS [complementary metal oxide semiconductor] compatible material with several active and passive photonic applications,” Su says. “We're looking at specifically amorphous germanium because it is easier to deposit than crystalline germanium, and therefore lower cost.” A crystalline structure is highly ordered at the molecular level, while an amorphous structure is more disordered.

    During a visit to the lab, Kosciolek and Su explain the process they use to fabricate these germanium thin films, removing a bare silicon wafer from the process chamber and reapplying tape before reinserting it. To remove the sample from the pressurized main chamber, which is under vacuum, they first have to open the valves connecting the load lock to the process chamber and equalize the pressure. “After we pull the sample out of the process chamber and into the load lock, we can then close the valve and then vent the load lock, so that we can take out the sample. The sample currently is just the silicon wafer,” Kosciolek explains.

    “We use a special tool called a profilometer that lets us measure the thickness of the sample,” he says. “An easy way to use it is just apply tape beforehand so that there's a very clear distinct ledge between where the sample is and where it ends.” Su adds, “We're just going to adjust the tape a little bit so that we can get a more distinct edge for that profilometer measurement to measure the thickness. What the tape is doing is securing the sample to our sample holder plate, but we also are simultaneously using that piece of tape to create an edge where we have germanium and then suddenly no germanium, and that ledge right there allows us to measure the thickness using a profilometer.”

    Summer Scholar Photonics Ryan Kosciolek 9117 DP Web
    AIM Photonics Academy summer intern Ryan Kosciolek works with amorphous germanium, depositing thin films of that material and characterizing the optical, electrical, and material properties to evaluate its use for photonic applications. Here he stands at the control panel for the thin film, sputter deposition machine. Photo, Denis Paiste, Materials Processing Center.

    After adjusting the sample and the tape, Kosciolek says, they can put it back in the thin film, sputter deposition chamber, first placing it onto the lever arm in the load lock. “After closing the load lock, we can then go back to the control panel and use the pumps to vacuum it down,” he says. He can then move the lever arm containing the sample into the process chamber. “Then we can raise the sample
    inside the process chamber, remove the lever arm, and once again close the valve. Once it's at a sufficiently low pressure, we can then run the deposition.” Kosciolek also hopes to fabricate waveguides from the amorphous germanium material.

    Kosciolek is a physics and mathematics major at Rutgers. His AIM Photonics Academy internship is part of the “AIM Photonics Future Leaders: Research and Professional Skills Training Program,” with additional support from the Materials Processing Center and the Center for Materials Science and Engineering. AIM Photonics interns from MIT, the University California, Santa Barbara [UCSB], University of Arizona and SUNY Polytechnic Albany convened at UCSB Aug. 10-11, 2017.

    Denis Paiste, Materials Processing Center
    August 28, 2017

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    Summer Scholar Photonics Ryan Kosciolek 9186 DP Web
    AIM Photonics Academy summer intern Ryan Kosciolek presents his research on amorphous germanium materials during the MPC-CMSE Summer Scholars Poster Session on Aug. 3, 2017.