This paper discusses the recent advancement in understanding of the nature of carrier recombination in wide InGaN/GaN quantum wells (QWs). The large electric field present in InGaN/GaN QWs separates the electron and hole wavefunctions, which leads to reduction of the oscillator strength. It might seem that increasing the thickness of the QW would only exaggerate this problem. For this reason the wide InGaN/GaN QWs are commonly regarded as not useful in optoelectronic devices. We show that wide InGaN QWs are in fact highly efficient, which is explained with a complex recombination mechanism. Upon excitation, charge carriers accumulate, due to lack of recombination, and screen the built-in field. As the field becomes weaker, the band structure changes, until a new recombination path is created. Surprisingly, this new path is more efficient then in standard thin InGaN/GaN QWs. Interestingly, the carrier recombination occurs solely through excited states, while the ground states are confined close to interfaces and still lack overlap with each other. A comprehensive study involving light emitting diodes, laser diodes and advanced modeling is presented to understand the behavior of this quantum system. Time-resolved electroluminescence studies of laser diodes with wide InGaN/GaN quantum wells reveal that the nature of the system shifts from a 2D quantum confinement to a 3D bulk-like structure as more carriers are injected into the active region. Furthermore, by means of gain spectroscopy performed on laser diodes and complementary kp calculations we study the material gain of InGaN/GaN quantum wells. We show that wide InGaN QWs can be beneficial for optoelectronic devices.

Perhaps you have grown beautiful forests of free-standing semiconductor nanowires. Or maybe you have exfoliated many flakes of a two-dimensional semiconductor. These materials are relatively easy to obtain and their atomic composition and structure can be determined accurately using electron microscopy. With nanowires, you may have benefited from the ability to grow highly mismatched heterostructures and attained unusual emission wavelengths impossible with standard planar epitaxial methods. With the 2D semiconductors, you have found unusual transport phenomena or realized advantages of the large surface to volume ratios. Perhaps you are experimenting with fabrication on flexible substrates hoping to exploit the many opportunities open to a less expensive manufacturing technique. This talk will describe a few examples from our own studies on nanowires and 2D materials where unusual junctions and sensors were demonstrated [1-6]. I will also endeavor to ask how successful has the field been towards the application of nanowires or 2D materials into green energy applications. Where do these material systems excel? Acknowledgements, NSERC. References 1. Thushani de Silva, Mirette Fawzy, et al., “Ultrasensitive rapid cytokine sensors based on asymmetric geometry two-dimensional MoS2 diodes”, Nature Comm. 22, 18274 (2022). 2. Christoph Herrmann, Miriam Rath, Christian Kumpf and Karen L. Kavanagh, “Rotational Epitaxy of h-BN on Cu (110)”, Surf. Sci. 721, 122080 (2022). 3. Mingze Yang, Ali Darbandi, Simon P. Watkins, and Karen L. Kavanagh, “Geometric effects on carrier collection in core-shell nanowire p-n junctions”, Nano Futures 5, 025007 (2021). 4. Clayton W. Schultz, Mirette Fawzy, Farzad Nasirpouri, Karen L. Kavanagh, and Hua-Zhong Yu, “Three-Dimensional Conductive Fingerprint Phantoms Made of Ethylene-Vinyl Acetate/Graphene Nanocomposite for Evaluating Smartphone Scanners”, ACS Appl. Elec. Matls. 3, 2097 (2021). 5. Cristina Cordoba, Taylor Teitsworth, Mingze Yang, James Cahoon, and Karen L. Kavanagh, “Abrupt degenerately doped, silicon nanowire, tunnel junctions”, Nanotechnol. 31, 415708 (2020). 6. Ali Darbandi, James C. McNeil, Azadeh A Zavareh, Simon P. Watkins, and Karen L. Kavanagh, “Direct Measurement of the Electrical Abruptness of a Nanowire p-n Junction”, Nano Letters 16, 3982-3988 (2016). (DOI: 10.1021/acs.nanolett.6b00289) 7. Karen L. Kavanagh, Igor Saveliev, Marina Blumin, Greg Swadener, and Harry E. Ruda, “Faster radial strain relaxation in InAs-GaAs core-shell heterowires”, J. Appl. Phys. 111 (2012) 093516.

Amorphous Indium-Gallium-Zinc-Oxide thin film transistors gained commercial success in back panel display applications owing to its high mobility, high on/off ratio, and low subthreshold swing (SS). In this work, we study the current-voltage characteristics and mobility of reactive-sputtered IGZO-based TFTs, varying the deposition parameters. Our study indicates that lower oxygen flow during deposition and annealing result in improved device performance. This can drive an array of nano-LEDs and enable the heterogeneous integration of the two devices for high-resolution display applications.

High purity silicon is currently produced through a two-step process consisting of the carbothermal reduction of silica in submerged electric arc furnaces to form metallurgical grade silicon followed by the Siemens process involving trichlorosilane to produce electronic grade polycrystalline silicon (polySi). The current standard polySi manufacturing process is energy-intensive and has a large emissions footprint. This paper examines laser-driven approaches for polySi production to achieve higher energy efficiency and lower the environmental impact of silicon manufacturing.