Role of Surface Chemistry of Ta Metal Foil on the Growth of GaN Nanorods by Laser Molecular Beam Epitaxy and Their Field Emission Characteristics

This study investigates the influence of surface nitridation of Ta metal foil substrates on the growth of GaN nanorods using the laser molecular beam epitaxy (LMBE) technique and the field emission characteristics of the grown GaN nanorod ensemble. Surface morphology examinations underscore the pivotal role of Ta foil nitridation in shaping the dimensions and densities of GaN nanorods. Bare Ta foil fosters the formation of high-density, vertically self-aligned GaN nanorods at a growth temperature of 700 °C. Furthermore, the density of these nanorods is directly related to the duration of Ta foil nitridation, with increased duration leading to a reduced nanorod density. X-ray Photoelectron Spectroscopy (XPS) studies reveal that the transition of the Ta foil surface from tantalum oxide to tantalum nitride during nitridation emerges as a crucial factor influencing GaN nanorod growth. Photoluminescence (PL) spectroscopy at ambient temperature reveals a strong near-band-edge (NBE) emission peak with negligible defect-related peaks, displaying the high optical quality of the GaN nanorods. The highly dense vertically aligned GaN nanorod ensemble growth without Ta prenitridation exhibits the most favorable field emission performance, featuring a turn-on field of 2.1 V/μm, a field enhancement factor of 2480, and a stable long-term operation at the emission current density of 2.26 mA/cm2. This study advances the understanding of the role of the surface chemistry of metal foil in determining GaN nanorod growth and opens up exciting possibilities for tailoring advanced optoelectronic devices for specific application requirements.

Flexible perylenediimide/GaN organic-inorganic hybrid system with exciting optical and interfacial properties

We report the band gap tuning and facilitated charge transport at perylenediimide (PDI)/GaN interface in organic–inorganic hybrid nanostructure system over flexible titanium (Ti) foil. Energy levels of the materials perfectly align and facilitate high efficiency charge transfer from electron rich n-GaN to electron deficient PDI molecules. Proper interface formation resulted in band gap tuning as well as facilitated electron transport as evident in I–V characteristics. Growth of PDI/GaN hybrid system with band gap tuning from ultra-violet to visible region and excellent electrical properties open up new paradigm for fabrication of efficient optoelectronics devices on flexible substrates.

Synthesis, structure and optimized field emission properties of highly oriented ZnO/Pt core–shell nanorods on a Zn substrate

The current density of as-fabricated Pt15/ZnO NR emitters was about 1900 times that of the bare ZnO emitters.

Catalytic Growth of Gallium Nitride Nanowires on Wet Chemically Etched Substrates by Chemical Vapor Deposition

Growth of gallium nitride nanowires on etched sapphire and GaN substrates using binary catalytic alloy were investigated by manipulating the growth time and precursor-to-substrate distance. The variations in behavior at different growth conditions were observed using X-ray diffractometer, Raman spectroscopy, X-ray photoelectron spectroscopy, cathodoluminescence spectroscopy, optical microscopy, atomic force microscopy, and scanning electron microscopy. It was noticed that, in respect of both the substrates, when growth time and/or precursor-to-substrate distance is increased, thickness of the nanowires around the etch pits remains unaltered, but there is variation in the density of nanowires. In addition, formation of gallium nitride microwires within the etch pits was also observed on etched sapphire substrates. Similarly, the thickness and density of the microwires were found to increase with increase in growth time and decrease with increase in precursor-to-substrate distance. The dimensionality scaling of gallium nitride was found to have a positive effect in improving the luminescence property and band gap of the grown nanowires. This method of nanowire growth can be helpful in increasing the probability of multiple reflections in the materials which makes them a suitable candidate for optoelectronic devices.