Roberto Paiella

Manufacturing of Group-IV Semiconductor Nanomembranes for Laser Applications

PROJECT DESCRIPTION
The development of practical light sources based on group-IV semiconductors (the leading materials platform of microelectronics) represents one of the major outstanding challenges of optoelectronics research. This goal, which is complicated by an intrinsic material property of Si, Ge, and related alloys (their indirect energy bandgap), has far reaching technological implications, as it would enable the monolithic integration of electronic and photonic functionalities on an unprecedented scale. Of particular interest in this context is the predicted ability of biaxial tensile strain in Ge to reduce the difference between the direct and indirect bandgap energies, until (at a strain level of about 1.9 %) Ge is even converted into a direct-bandgap semiconductor.

Recent work in the Paiella group has shown that the required strain levels can be achieved in mechanically stressed Ge nanomembranes (NMs), i.e., single-crystal sheets with nanoscale thicknesses that are either completely released from, or partially suspended over, their native substrates. With this approach we have demonstrated the formation of direct-bandgap Ge with highly enhanced radiative efficiency, and capable of supporting population inversion under realistic pumping conditions. Furthermore, we have developed photonic-crystal cavities compatible with the highly-subwavelength thicknesses and mechanical-flexibility requirements of NM gain media. Ongoing work is aimed at minimizing the cavity losses to enable laser action.

LEARNING GOALS
• Basic skills in micro- and nano-fabrication technologies, involving both rigid inorganic semiconductors and soft polymeric materials.
• Several key concepts in optoelectronics, particularly related to the development and characterization of semiconductor light emitting devices.

Learn more about Professor Paiella’s work on his lab website.