Raman Analysis of E2 (High) and A1 (LO) Phonon to the Stress-Free GaN Grown on Sputtered AlN/Graphene Buffer Layer

Piezoelectricity in wide bandgap semiconductor 2D crystal GaN nanosheets

Gallium nitride (GaN) exhibits various potential applications in optics and optoelectronics due to its outstanding physical characteristics, including a wide direct bandgap, strong deep-ultraviolet emission, and excellent electron transport properties. However, research on the piezoelectric and related properties of GaN nanosheets are scarce, as previous small-scale GaN investigations have mainly concentrated on nanowires and nanotubes. Here, we report a strategy for growing 2D GaN nanosheets using chemical vapor deposition on Ga/W liquid-phase substrates. Additionally, utilizing scanning probe techniques, it has been observed that 700 nm-thick GaN nanosheets demonstrate a piezoelectric constant of deff33 = 1.53 ± 0.21 pm V-1 and possess the capability to effectively modulate the Schottky barrier. The piezoelectric characteristics of 2D GaN are offering new options for innovative applications in various fields, including energy harvesting, electronics, sensing, and communications.

Synthesis, Properties, and Application of Ultrathin and Flexible Tellurium Nanorope Films: Beyond Conventional 2D Materials

Nanomaterials that can be easily processed into thin films are highly desirable for their wide range of applicability in electrical and optical devices. Currently, Te-based 2D materials are of interest because of their superior electrical properties compared to transition metal dichalcogenide materials. However, the large-scale manufacturing of these materials is challenging, impeding their commercialization. This paper reports on ultrathin, large-scale, and highly flexible Te and Te-metal nanorope films grown via low-power radiofrequency sputtering for a short period at 25 °C. Additionally, the feasibility of such films as transistor channels and flexible transparent conductive electrodes is discussed. A 20 nm thick Te-Ni-nanorope-channel-based transistor exhibits a high mobility (≈450 cm2 V-1 s-1 ) and on/off ratio (105 ), while 7 nm thick Te-W nanorope electrodes exhibit an extremely low haze (1.7%) and sheet resistance (30 Ω sq-1 ), and high transmittance (86.4%), work function (≈4.9 eV), and flexibility. Blue organic light-emitting diodes with 7 nm Te-W anodes exhibit significantly higher external quantum efficiencies (15.7%), lower turn-on voltages (3.2 V), and higher and more uniform viewing angles than indium-tin-oxide-based devices. The excellent mechanical flexibility and easy coating capability offered by Te nanoropes demonstrate their superiority over conventional nanomaterials and provide an effective outlet for multifunctional devices.

Investigations on the high performance of InGaN red micro-LEDs with single quantum well for visible light communication applications

In this study, we have demonstrated the potential of InGaN-based red micro-LEDs with single quantum well (SQW) structure for visible light communication applications. Our findings indicate the SQW sample has a better crystal quality, with high-purity emission, a narrower full width at half maximum, and higher internal quantum efficiency, compared to InGaN red micro-LED with a double quantum wells (DQWs) structure. The InGaN red micro-LED with SQW structure exhibits a higher maximum external quantum efficiency of 5.95% and experiences less blueshift as the current density increases when compared to the DQWs device. Furthermore, the SQW device has a superior modulation bandwidth of 424 MHz with a data transmission rate of 800 Mbit/s at an injection current density of 2000 A/cm². These results demonstrate that InGaN-based SQW red micro-LEDs hold great promise for realizing full-color micro-display and visible light communication applications.

Two-In-One: End-Emitting Blue LED and Self-Powered UV Photodetector based on Single Trapezoidal PIN GaN Microwire for Ambient Light UV Monitoring and Feedback

With the continuous miniaturization and integration of the semiconductor industry, micro/nanoscale integrated photonics has received extensive attention as a key technology for optical communication, optical storage, and optical interconnection. Here, a two-in-one device is reported with both unidirectional blue light emission and UV photodetection functions based on single trapezoidal PIN GaN microwire. By constructing a Fabry-Perot resonator cavity structure, the end-emitting blue light-emitting diode with a low turn-on voltage (≈0.97 V) and high color purity (full width at half maximum ≈22 nm) is implemented. Furthermore, benefiting from the slow growth rate of the semipolar planes on both sides of the trapezoidal microwire and the high diffuse reflectivity of the patterned substrate, the trapezoidal microwire sides can be used as a high-performance UV photodetector. In self-driven mode, the device exhibits a large responsivity (0.218 A W^-1 ), high external quantum efficiency (83.31%) and fast response speed (rise/decay time of 0.48/0.98 ms). Finally, the prepared two-in-one device is successfully integrated into ambient light UV monitoring and feedback system and tested. This work provides a novel strategy to combine luminescence with photodetection, demonstrating high potential for applications, such as on-chip photonic integration, energy-saving communication and ambient light monitoring and feedback system.

The Influence of Aminoalcohols on ZnO Films’ Structure

Preparing structures with the sol-gel method often requires control of the basal plane of crystallites, crystallite structures, or the appearance of the voids. One of the critical factors in the formation of a layer are additives, such as aminoalcohols, which increase the control of the sol formation reaction. Since aminoalcohols differ in boiling points and alkalinity, their selection may play a significant role in the dynamics of structure formation. The main aim of this work is to examine the properties of ZnO layers grown using different aminoalcohols at different concentration rates. The layers were grown on various substrates, which would provide additional information on the behavior of the layers on a specific substrate, and the mixture was annealed at a relatively low temperature (400 °C). The research was conducted using monoethanolamine (MEA) and diethanolamine (DEA). The aminoalcohols were added to the solutions in equal concentrations. The microscopic image of the structure and the size of the crystallites were determined using micrographs. X-ray diffractometry and Raman spectroscopy were used for structural studies, phase analysis and to establish the purity of the obtained films. UV-vis absorption and photoluminescence were used to evaluate structural defects. This paper shows the influence of the stabilizer on the morphology of samples and the influence of the morphology and structure on the optical properties. The above comparison may allow the preparation of ZnO samples for specific applications.

MicroRaman Study of Nanostructured Ultra-Thin AlGaN/GaN Thin Films Grown on Hybrid Compliant SiC/Por-Si Substrates

In our study, for the first time we demonstrate the advantages of using a compliant hybrid substrate of porSi/SiC to grow high-quality ultra-thin nanostructured AlxGa1−xN/GaN heterostructures using molecular beam epitaxy with plasma-activated nitrogen. Comparison of our experimental results obtained by micro-Raman spectroscopy, deconvolution, and the fitting of the experimental Raman spectra and subsequent calculations with information from already established literature sources show that the use of such a hybrid SiC/porSi substrate has a number of undeniable advantages for the growth of ultra-thin AlxGa1−xN/GaN nanoheterostructures without requiring the use of thick AIIIN buffer layers. Direct growth on a hybrid compliant substrate of SiC/porSi leads to a substantial relaxation in the elastic stresses between the epitaxial film, porous silicon, and silicon carbide, which consequently affects the structural quality of the ultra-thin AlxGa1−xN/GaN epitaxial layers. The experimental and computational data obtained in our work are important for understanding the physics and technology of AlxGa1−xN/GaN nanoheterostructures and will contribute to their potential applications in optoelectronics.

Improvement in the Output Power of Near-Ultraviolet LEDs of p-GaN Nanorods through SiO2 Nanosphere Mask Lithography with the Dip-Coating Method

In this paper, the conditions of the dip-coating method of SiO₂ nanospheres are optimized, and a neatly arranged single-layer SiO₂ array is obtained. On this basis, a "top-down" inductively coupled plasma (ICP) technique is used to etch the p-GaN layer to prepare a periodic triangular nanopore array. After the etching is completed, the compressive stress in the epitaxial wafer sample is released to a certain extent. Then, die processing is performed on the etched LED epitaxial wafer samples. The LED chip with an etching depth of 150 nm has the highest overall luminous efficiency. Under a 100 mA injection current, the light output power (LOP) of the etched 150 nm sample is 23.61% higher than that of the original unetched sample.