SCIENTIFIC HIGHLIGHTS

In-depth analysis of novel semiconductor polymorphs

A combination of Raman spectroscopy and theoretical calculations provides unprecedented insight into crystal phase engineering in semiconducting nanostructures
Recent advances in the synthetic growth of nanowires --rod shaped semiconductors of nanometric size-- have given access to crystal phases that in bulk are only observed under extreme pressure conditions. The advent of these novel polymorphs, such as hexagonal Ge, promises to overcome some of the limitations that have prevented them to find application in photonics and optoelectronics thus far. The bandgap of hexagonal Ge is predicted to be direct, a fact that could have important implications with respect to the long-standing goal of designing a Ge-based light-emitting materials. Experimental data on these novel materials are scarce and are sometimes limited by the quality of the sample.

In this work, we used Raman spectroscopy, a common technique to probe the vibrational properties of materials and demonstrate its versatility when it comes to the determination of the main crystalline, phononic, and electronic properties of one of the most challenging type of nanostructure: a nanoscale sample with constant material composition, but different crystal phases. Theoretical calculations played a crucial role in understanding and interpreting the experimental results, especially because, due to its novelty, there are no reference data on hexagonal Ge.

The general procedure that we establish can be applied to several types of nanostructures. 

Authors

  • Claudia Fasolato1, Marta De Luca1, Doriane Djomani2, Laetitia Vincent2, Charles Renard2, Giulia Di Iorio1, Vincent Paillard3, Michele Amato4, Riccardo Rurali5, and Ilaria Zardo1
  • Affiliations:

    1Departement Physik, Universität Basel, Switzerland
    2Centre de Nanosciences et Nanotechnologies (C2N), CNRS, Univ. Paris-Sud, UniversitéParis-Saclay, France
    3CEMES, University of Toulouse, CNRS, France
    4Laboratoire de Physique des Solides (LPS), CNRS, Univ. Paris-Sud, Université Paris-Saclay, France
    5Institut de Ciència de Materials de Barcelona (ICMAB−CSIC), Spain
  • Publication

    Crystalline, Phononic, and Electronic Properties of Heterostructured Polytypic Ge Nanowires by Raman Spectroscopy
    Nano Letters, 18, 11, 7075-7084 (2018)
    DOI: 10.1021/acs.nanolett.8b03073

  • Figure

    Artist view of a heterostructured Ge nanowire where cubic (in red) and hexagonal (in dark yellow) domains are alternated. Sketches of the Raman spectra acquired are also shown. Two segments of the nanowire are textured with the corresponding TEM image.

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