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PhD Thesis Proposal: Shang Liu



2:30pm - 4:00pm ET

Jackson Conf Rm, Cummings Hall/Online

To attend via Zoom, please email

"GeSn on Si for Integrated Photonics and Integrated Quantum Materials"


The utilization of infrared (IR) imaging has become paramount in various fields, including night vision, autonomous driving, medical sciences, and climatology. In light of the high demand for infrared imaging, the development of low-cost, high-performance infrared detectors with large-pixel array have become a focal point of interest within the infrared sensing community. Currently, the IR imaging industry is dominated by detectors based on II-VI materials, such as mercury cadmium telluride (HgCdTe), and III-V materials, such as indium gallium arsenide (InGaAs). But these detectors are hindered by complex fabrication processes, low production yields, and high costs.

GeSn alloys are promising group IV materials for IR imaging due to their capability of tuning direct bandgap and potentially compatibility with Si integrated circuits. However, their synthesis on Si remains an ongoing challenge, especially for Sn composition larger than 10% as the equilibrium solid solubility of Sn in Ge is less than 1%. Our group has developed a method to directly grow crystalline GeSn (with Sn composition up to 15%) on Si using physical vapor deposition (PVD) and rapid thermal annealing (RTA). This method is proposed here as a means to integrate the GeSn into Si CMOS image sensor (CIS) chip for IR image detection.

Recent theoretical prediction has indicated that short-range order (SRO) exists in GeSn alloys and profoundly impacts the band structure. Guided by physics-informed Poisson statistical analyses of k-nearest neighbors (KNN) in atom probe tomography (APT), a new approach is proposed here for 3D nanoscale SRO mapping in GeSn. This work will set a foundation for further engineering the band structure of GeSn through SRO control by tuning growth conditions.

While Ge-rich GeSn alloys encounter great opportunity for integrated photonics, Sn-rich GeSn alloys hold potential for quantum material integration. α-Sn has been identified as a topological quantum material, but bulk α-Sn is thermodynamically stable only below 13oC and its integration on Si is hindered by the large lattice mismatch. Here, we also propose a new method to grow Ge-doped α-Sn on silicon by annealing at 300–500oC.

Thesis Committee

  • Prof. Jifeng Liu (advisor, Chair)
  • Prof. Eric Fossum
  • Prof. Hui Fang


For more information, contact Theresa Fuller at