Session Index

We will present nano-scale correlation of structural, electronic and optical properties of nitride-based heterostructures using cathodoluminescence and electron-beam induced current directly performed in a scanning transmission electron microscope. Typical results exhibiting the complex nano-transport of excess carriers, in particular charge carriers and/or excitons, due to a specific heterostructure design of a device will be presented.


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This work investigates the optical properties of (Al,Ga)N heterostructures emitting between 310nm and 209nm. Photoluminescence (PL) analyses were conducted on thick epilayers, single and multiple quantum wells. Full width at half maximum of the PL, orientations and shapes of the on-side emission diagram, and PL intensity were analyzed by taking into account valence band symmetry, Quantum Confined Stark Effect, and 2D carrier localization.
This work was supported by ANR funding GANEX (ANR-11-LABX-0014) and DOPALGAN .

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We characterized two UVC light-emitting diode (LED) epi wafers by high-resolution scan transmission electron microscopy (HR-STEM) and atom probe tomography (APT). Geometry phase analysis with HR-STEM revealed the sample grown on the more compressively strained template possesses a more pronounced local lattice constant distortion in the multiple-quantum-well (MQW) region. APT further verified the local lattice distortion originated from the strain-induced Ga segregation in the MQW. The nanoscopic compositional fluctuation favors AlGaN growth front destabilization and triggers new defect nucleation, which explains the atomistic origin of strain-induced morphology and performance degradation in UVC LEDs.

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Green hydrogen generation through photoelectrochemical water splitting (PEC-WS) is regarded as one of the most environmentally friendly hydrogen generation methods. III-nitride semiconductors are promising photoanode materials due to their tunable bandgap (UV to NIR) and favorable alignment with water redox potentials. However, their application in direct seawater PEC-WS is hindered by surface defects, limited surface area, and severe energy band bending. This study demonstrates that GO/GaN photoanodes enhance charge transport and improve photoelectrode stability through graphene oxide passivation, offering an effective strategy to overcome existing limitations and enable efficient hydrogen generation from direct seawater.

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The demand for high-power, high-frequency electronics drives GaN-based high electron mobility transistor (HEMT) development. To suppress threading dislocations (TDs) that cause leakage, SiNₓ nano-mask was incorporated into AlGaN/GaN HEMTs on Si(111). Effects of varying SiH₄ flow rates during MOCVD growth were studied. Cathodoluminescence spectroscopy visualized TDs density, confirmed uniformity, and assessed optical properties, supported by Raman and electrical characterization. At 50 sccm SiH₄, the defect-to-free-exciton emission ratio was minimized, and breakdown voltages improved (1710 V to 1780 V, 411 V to 448 V). Comprehensive understanding of SiNₓ nano-mask effects enables substantial improvements in GaN-based HEMT crystal quality and device performance.

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This study compares β-Ga₂O₃ PN heterojunctions grown using TMGa and TEGa sources. Devices were fabricated with identical metal contacts and annealing parameters, and evaluated for their electrical characteristics. TMGa-grown devices showed higher on/off ratio and higher breakdown voltage, while TEGa-grown structures demonstrated superior ideality factors. The results highlight trade-offs between precursor choice and Ga₂O₃ device performance.

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This study investigates the integration of nickel oxide (NiO), deposited 100 nm at room temperature by sputtering, as the gate dielectric in AlGaN/GaN high electron mobility transistors (HEMTs). Devices were fabricated with post-deposition annealing (PDA) at various temperatures (600 °C, 700 °C, 800 °C). Electrical characteristics including threshold voltage (Vth), transconductance (gm), breakdown voltage, and mobility were analyzed. The device annealed at 700 °C exhibited the highest gm,max (57.35 mS/mm), improved Vth (−1.79 V), and breakdown voltage (~1103 V). The results indicate annealing NiO deposition enhances device performance, positioning room-temperature NiO as a viable gate dielectric for high-performance GaN-based electronics.

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