High-quality indium gallium nitride baskets revealed by their differential indium content
High-quality indium gallium nitride baskets revealed by their differential indium content lead image
Indium gallium nitride both emits and absorbs light, and is widely used in white light-emitting diodes and laser diodes, and has growing importance in applications such as concentrating solar cells. Under concentration, higher temperatures decrease the efficiency of conventional silicon devices, which reduces their low-cost advantage. Indium gallium nitride, while more expensive, becomes cost competitive at high concentrations. Lattice imperfections that develop during the thicker film growth needed for solar cells, however, are still somewhat mysterious and pose significant challenges to its large scale use in devices.
Research from Wang et al. discovered a new mechanism for plastic deformation during the growth of indium gallium nitride, revealing that a medium-scale indium content causes lattice mismatch between regions with different molecular concentrations. The authors focused on mechanisms of the strain relaxation for indium content between 7 and 15 percent, a range that is not well-understood in the literature. Their work discovers defect-free baskets that contain a higher indium content, which form due to lattice mismatch relaxation of the grown material
The authors probed the nature of the material using transmission electron microscopy enabled with energy dispersive X-ray spectroscopy. This allowed them to locate and identify the types of dislocations and faults and discover the dislocation clusters that resembled baskets.
With cathodoluminescence on a scanning electron microscope, they then probed the optical characteristics of the material at specific locations. The observed dislocation baskets contained defect-free material with a higher indium content than that of the surrounding matrix, which has been identified by the smaller bandgap observed by luminescence spectroscopic imaging with very high spatial resolution.
The revelations of this work could enable larger-scale, high-quality indium gallium nitride devices with specified indium content for tailorable bandgaps to provide desirable properties for high-temperature applications.
Source: “Dislocation baskets in thick InxGa1-xN epilayers,” by Shuo Wang, Hongen Xie, Hanxiao Liu, Alec M. Fischer, Heather McFavilen, and Fernando A. Ponce, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5042079 .
