Energy and Climate
This research challenge explores the synthesis and properties of GaN/InGaN nanowires as a materials architecture for visible light-emission. If nanowire devices could span the entire visible spectrum, the RYG-gap technology challenges would be overcome. In addition, such full-spectrum emission would enable chromaticity-tunable light, which could also impact so-called smart (or higher functionality) lighting, another technology challenge.

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Among  InGaN nanowires’ many advantages over presently-employed planar InGaN films are:

  • the potential for high-quality material, without detrimental line defects;
  • the ability to accommodate lattice strain and therefore a wider range of alloy compositions and bandgaps;
  • the manipulability of growth geometries so as to expose surface orientations with tailored light emission properties;
  • its compatibility with novel nanoscale intrawire and interwire energy transfer processes.

That said, InGaN nanowires are a relatively immature materials architecture. Thus, this research challenge is wide-ranging in scope, encompassing materials synthesis and processing of both photo- and electro-luminescent structures, and optical, electrical, mechanical and structural characterization.

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Our initial work in this research challenge focused on a bottom-up fabrication method based on highly anisotropic metal-catalyzed epitaxy (the deposition of an overlayer on a crystalline substrate where the overlayer is in registry with the substrate). We also initiated exploratory work on a top-down fabrication method, based on a sequence of planar epitaxy, anisotropic dry and wet etching, and subsequent radial and vertical epitaxy. This top-down method has shown sufficient promise for us to shift our focus entirely to it.

The top-down method enables higher opto-electronic material quality, an ability to create both axial and radial heterostructures, (the interface between two layers or regions of dissimilar semiconducting materials that have unequal bandgaps), and increased control over nanowire periodicity and uniformity – all critical for individual and arrayed electroluminescent light-emitting nanowire devices. As we go forward, we anticipate our focus to be on using this top-down method to fabricate nanowires with electroluminescence in the visible-light spectrum. We will emphasize the longer green-yellow-red wavelengths that are difficult to achieve in planar architectures and using nanowires as a cross-cutting materials architecture for the other research challenges focusing on light-emission phenomena in our EFRC.

Indeed, we note here that progress in nanowire research in our laboratory and others has reached the point of enabling what we believe will be a wide range of nanowire architectures tailored to exhibit phenomena of importance to SSL and beyond.

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(a) Ordered GaN nanowire array (~2 µm height) fabricated using our new top-down process; (b) top-down fabricated flashlight-shaped axial InGaN/GaN single nanowire LED; (c) yellow-red electroluminescence from a vertically integrated array of radial InGaN/GaN nanowire LEDs.

Research Participants

  • Dr. George Wang (SNL) – Principal Investigator – determines research goals and priorities, directs/coordinates team, oversees work, and interfaces with other research challenges.
  • Dr. Andrew Armstrong (SNL) – Deep level optical spectroscopy (DLOS) of nanowires.
  • Dr. Igal Brener, Dr. Willie Luk and Jeremy Wright (Ph.D student) (SNL/UNM) – Study and control of nanowire lasing properties using optical spectroscopy and modeling.
  • Prof. Lincoln Lauhon and Jim Riley (Ph.D student) (Northwestern) –3D atom probe tomography (APT), and Raman spectroscopy analysis of nanoscale variations in structure and composition.
  • Dr. Francois Leonard (SNL) – Theoretical modeling of nanowire electronic structure.
  • Dr. Rohit Prasankumar (LANL) – Ultrafast optical studies of nanowire carrier dynamics.
Research Challenge Publications

 

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