GaN Nano Research Articles

Dodecagonal GaN Microrods: Chemical Stability of a‐, m‐, and c‐Plane Walls and Their Application to Water‐Splitting

AbstractPhotoelectrolysis of water is a sustainable option for the production of hydrogen fuel. GaN nano‐ or microstructures are considered for water‐splitting due to their general high chemical stability and high surface‐to‐volume ratio enhancing the process effectiveness. In this study GaN structures with dodecagonal microrods are used as a working electrode for the water‐splitting process. Microrods are grown using a plasma‐assisted molecular beam epitaxy process allowing tailoring of microrod height and density. Their unique property is the of presence twelve sidewalls with alternating a‐ and m‐plane orientations. This enables a simultaneous study of the chemical stability of c‐, a‐, and m‐plane walls of GaN. The water‐splitting process is performed using a 1 mol l−1 NaOH electrolyte solution. Non‐zero current measured at zero bias under illumination indicates that the process takes place. A degradation of the GaN structure is observed after a prolonged process time. In short‐term exposures, etching of microrod sidewalls is observed. Roughening of the a‐plane walls studied by transmission electron microscopy indicates that this orientation is etched with a fastest rate. The internal crystalline structure is not influenced by the etching and remains stable as shown by the X‐ray absorption spectroscopy study.

Impact of radiation damage on the photoconductor and photodiode properties of GaN core–shell p–n junction microwires

GaN nano- and microwires have gained increasing interest due to their unique geometry and flexibility, and have already been successfully applied in optoelectronics. One important advantage is their superior crystalline quality in comparison to their thin-film counterparts. Beside this, GaN is also known for its high radiation hardness, owed to the large displacement energy of the atoms in its crystal lattice and efficient dynamic annealing properties. In this work, single GaN core–shell p–n junction microwires have been processed into radiation detectors and the induced damage effects on the electrical and optoelectrical characteristics, when irradiating the detectors with 1 and 2 MeV protons, have been studied. By measuring the dark and photocurrent as a function of the irradiation fluence we show that for fluences up to 1×1014 protons/cm2 there is no significant modification of any of the parameters and that serious degradation only occurs for fluences above 1×1015 protons/cm2. Furthermore, we also observe that the dark current decays at a lower irradiation fluence with respect to the photocurrent due to the different impact of the created irradiation defects on the properties of the neutral region and the p–n junction. As a consequence, the signal-to-noise ratio of the detector is strongly enhanced, especially when applying a higher reverse bias. Thermal treatments furthermore show that the degree of recovery of the properties of the detectors is strongly dependent on the irradiation fluence. The detector irradiated with a fluence of 5×1014 protons/cm2 almost completely retrieved its pre-irradiation characteristics whereas the detector irradiated with 5×1015 protons/cm2 only showed a minimal recovery.

GaN Nano Air Channel Diodes: Enabling High Rectification Ratio and Neutron Robust Radiation Operation.

Nano air channel transistors (NACTs) provide numerous advantages over traditional silicon devices, including faster switching speeds, higher operating frequencies, and enhanced radiation hardness attributable to the ballistic transport of electrons. In the development of field-emission-based integrated circuits, low-power consumption rectifying nano air channel diodes (NACDs) play a crucial role. However, achieving rectification characteristics in NACDs is challenging due to their structural and material symmetry. This paper proposes a vertical GaN NACD with a consistent nano air channel fabricated using IC-compatible processes. The GaN NACD exhibits an exceptionally low turn-on voltage of 0.3 V while delivering a high output current of 5.02 mA at 3 V. Notably, it demonstrates a high rectification ratio of up to 2.2 × 105, attributing to significant work function disparities within the GaN-Au structure, coupled with the reduction of Au surface roughness to minimize reverse current. Furthermore, the junction-free structure and superior material properties of GaN enable the NACD to be suitable for use in radiation-rich environments. With its potential as a fundamental component of ultrafast and ultrahigh-frequency integrated circuits, this intriguing and cost-effective rectifying diode is anticipated to garner widespread interest within the electronics community.

Toward ultrahigh efficiency GaN nano and micro full-color LEDs

Toward ultrahigh efficiency GaN nano and micro full-color LEDs

Publisher's Note: “Beyond solid-state lighting: Miniaturization, hybrid integration, and applications of GaN nano- and micro-LEDs” [Appl. Phys. Rev. 6, 041315 (2019)

Publisher's Note: “Beyond solid-state lighting: Miniaturization, hybrid integration, and applications of GaN nano- and micro-LEDs” [Appl. Phys. Rev. <b>6</b>, 041315 (2019)

Optical, surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method

ABSTRACTRoom-temperature ferromagnetism of GaN and doped GaN materials has been reported in nanostructured form. Especially, nanoparticles show ferromagnetic properties at room temperature. In this paper, Ti-doped effects on GaN were deposited on glass and Polyethylene terephthalate (PET) substrates by thermionic vacuum arc and their room temperature magnetic properties are presented for the first time. The structure of the Ti-doped GaN was crystallized in a novel form, nano honeycomb formation. Optical and surface properties of the nano honeycombs and honeycomb nanosheets were determined. GaN and TiN phases were detected in X-ray diffraction patterns. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) device were used for imaging of the crystal structure. According to FESEM images, hexagonal crystal formations were detected for all samples. Crystal formations are very good oriented on PET substrates materials according to glass samples. The band gap value of the sample is changed by crystallization dimension. It was found that increasing crystallizations and decreasing crystal dimensions were increased the band gap of the Ti-doped GaN approximately 50 meV. Fourier transform infrared spectra and a vibrating sample magnetometer results were presented. These results confirm the Ti doped GaN honeycomb nanosheets and nano honeycombs show the room temperature ferromagnetic properties.

Electron mobility of self-assembled and dislocation free InN nanorods grown on GaN nano wall network template

A kinetically controlled two-step growth process for the formation of an array of dislocation free high mobility InN nanorods (NRs) on GaN nanowall network (NWN) by Molecular Beam Epitaxy is demonstrated here. The epitaxial GaN NWN is formed on c-sapphire under nitrogen rich conditions, and then changing the source from Ga to In at appropriate substrate temperature yields the nucleation of a self assembled spontaneous m-plane side faceted-InN NR. By HRTEM, the NRs are shown to be dislocation-free and have a low band gap value of 0.65 eV. Hall measurements are carried out on a single InN NR along with J-V measurements that yield mobility values as high as ≈4453 cm2/V s and the carrier concentration of ≈1.1 × 1017 cm−3, which are unprecedented in the literature for comparable InN NR diameters.

Modeling of Noise Power Spectral Density Analysis for GaN/AlGaN HEMT

Nano Technology is the branch of technology that deals with dimensions and tolerances in terms of nanometers. In this paper, the electrical characteristics analysis is determined for the Nano-GaN HEMT and Micro-GaN HEMT and also power spectrum density is determined for GaN Nano-HEMT by reducing the gate length Lg in nm range. The GaN Nano HEMT is producing high current comparing to Micro GaN HEMT. Accuracy of the proposed analytical model results is verified with simulation results.

Electronic and optical properties of advance semiconductor materials: BN, AlN and GaN nanosheets from first principles

We investigate the electronic and linear optical properties of BN, AlN and GaN hexagonal nanosheets using the band structure results obtained through the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). The dielectric tensor and corresponding optical properties are derived within the random phase approximation (RPA). Specifically, the dielectric function, absorption coefficient, optical conductivity, extinction index, reflectivity, loss function and the refraction index of these above mentioned nanosheets are calculated for both parallel (E||x) and perpendicular (E||z) electric field polarizations. Calculated results show that the hexagonal XN (X=B, Al and Ga) nanosheets have semiconductor characters with wide band gap of about 4.96, 2.73 and 1.95eV respectively. The optical conductivity in E||x and E||z starts with a gap about 2.92eV and 6.73eV for BN, 2.73eV and 3.52eV for AlN and 1.61eV and 3.58eV for GaN, confirms that these nanosheets have semiconductor properties moreover the optical spectra are isotropic along these two polarizations. These results propose potential application for the development of BN, AlN and GaN nano structures in electronic and optoelectronic devices.

Three-dimensional Aerographite-GaN hybrid networks: Single step fabrication of porous and mechanically flexible materials for multifunctional applications

Three dimensional (3D) elastic hybrid networks built from interconnected nano- and microstructure building units, in the form of semiconducting-carbonaceous materials, are potential candidates for advanced technological applications. However, fabrication of these 3D hybrid networks by simple and versatile methods is a challenging task due to the involvement of complex and multiple synthesis processes. In this paper, we demonstrate the growth of Aerographite-GaN 3D hybrid networks using ultralight and extremely porous carbon based Aerographite material as templates by a single step hydride vapor phase epitaxy process. The GaN nano- and microstructures grow on the surface of Aerographite tubes and follow the network architecture of the Aerographite template without agglomeration. The synthesized 3D networks are integrated with the properties from both, i.e., nanoscale GaN structures and Aerographite in the form of flexible and semiconducting composites which could be exploited as next generation materials for electronic, photonic, and sensors applications.

Self‐organized growth of catalyst‐free GaN nano‐ and micro‐rods on Si(111) substrates by MOCVD

Our study shows the impact of the process parameters: predose before AlN buffer deposition, SiNx deposition time, GaN growth temperature and silane injection time on growth and morphology of GaN nanowires (NWs) formed by a self‐organized mechanism on a silicon substrate. We determined a process parameter window for successful GaN NW growth and show how the variation of studied parameters changes the NW morphology and density. The optimization of these process parameters led to high‐density straight GaN NWs, aligned perpendicular to the substrate. The use of a preflow before AlN buffer deposition was found to be important for the successful NW formation, and most interestingly, led to a difference in structural morphology for ammonia and TMAl predose.

Synthesis of GaN nano- and microwire crystals induced by a titanium nanolayer

The possibilities of a new method of growing gallium nitride nano- and microwire crystals using continuous titanium films with a thickness of 10–30 nm during growth are described. It is shown that this method can provide growth of high-quality GaN nanowire crystals at an extremely high rate of about 10 μm/min.

Facile synthesis and photoluminescence spectroscopy of 3D-triangular GaN nano prism islands.

We report a strategy for fabrication of 3D triangular GaN nano prism islands (TGNPI) grown on Ga/Si(553) substrate at low temperature by N2(+) ions implantation using a sputtering gun technique. The annealing of Ga/Si(553) (600 °C) followed by nitridation (2 keV) shows the formation of high quality GaN TGNPI cross-section. TGNPI morphology has been confirmed by atomic force microscopy. Furthermore, these nano prism islands exhibit prominent ultra-violet luminescence peaking at 366 nm upon 325 nm excitation wavelength along with a low intensity yellow luminescence broad peak at 545 nm which characterizes low defects density TGNPI. Furthermore, the time-resolved spectroscopy of luminescent TGNPI in nanoseconds holds promise for its futuristic application in next generation UV-based sensors as well as many portable optoelectronic devices.

Free standing GaN nano membrane by laser lift-off method

ABSTRACTIn this work, we present a method able to fabricate thin GaN nanomembranes fit for device applications. Starting from commercial GaN on sapphire substrates, MBE was used to deposit a sacrificial layer, which comprises of a superlattice of InN/InGaN, after which thin a GaN film of hundreds of nanometers thickness was grown on top. Pulsed laser irridiation with photon energy of 2.3eV gives rise to the controlled decomposition of the sacrificial intermediate layer, which can be followed by easy separation of the top GaN membrane from the substrate. This process can be used to manufacture GaN membranes with low defect density and a wider range of thickness. We demonstrated that large area, free-standing GaN membranes, with a thickness from 200nm and up, could be made using this method, and the high crystal quality of the lift-off GaN layers is well preserved in this process.

MOVPE에 의한 GaN 피라미드 꼭지점 위의 반극성 나노/마이크로 크기의 GaN 성장

We report on the growth and characterization of nano and micro scale GaN structures selectively grown on the vertex of hexagonal GaN pyramids. near the vertex of hexagonal GaN pyramids was removed by optimized photolithgraphy process and followed by a selective growth of nano and micro scale GaN structures by metal organic vapor phase epitaxy (MOVPE). The pyramidal GaN nano and micro structures which have crystal facets of semi-polar {1-101} facets were formed only on the vertex of GaN pyramids and the size of the selectively grown nano and micro GaN structures was easily controlled by growth time. As a result of TEM measurement, Reduction of threading dislocation density was conformed by transmission electron microscopy (TEM) in the selectively grown nano and micro GaN structures. However, stacking faults were newly developed near the edge of film because of the roughness and nonuniformity in thickness of the film.

Anti-reflective and hydrophobic surface of self-organized GaN nano-flowers

GaN nano flowers were grown on various commercial substrates by a simple catalyst free chemical vapor deposition (CVD) technique. The size and shape of the nanostructures were characterized by scanning electron microscopy (SEM). The influence of the substrate, growth temperature, and ammonia flow rate on the size and shape of the nano-flowers were investigated along with their anti-reflective and hydrophobic properties. The normal incident reflectivity measurements carried out on the nano structures showed very low (5%) reflectivity. The wettability of the surface investigated by the static contact angle of water droplet revealed their hydrophobic nature with a large contact angle of about 145°. These results on catalysis-free nanostructures would be useful for anti-reflective surfaces/coatings in solar cell applications.

GaN and ZnO nanostructures

AbstractGaN and ZnO are both wide band gap semiconductors with interesting properties concerning optoelectronic and sensor device applications. Due to the lack or the high costs of native substrates, alternatives like sapphire, silicon, or silicon carbide are taken, but the resulting lattice and thermal mismatches lead to increased defect densities which reduce the material quality. In contrast, nanostructures with high aspect ratio have lower defect densities as compared to layers. In this work, we give an overview on our results achieved on both ZnO as well as GaN based nanorods. ZnO nanostructures were grown by a wet chemical approach as well as by VPT on different substrates – even on flexible polymers. To compare the growth results we analyzed the structures by XRD and PL and show possible device applications. The GaN nano‐ and microstructures were grown by metal organic vapor phase epitaxy either in a self‐organized process or by selective area growth for a better control of shape and material composition. Finally we take a look onto possible device applications, presenting our attempts, e.g., to build LEDs based on GaN nanostructures.

Violet electroluminescence from p-GaN thin film/n-GaN nanowire homojunction

The difficulty associated with the precise positioning of nanowires has been one of the most significant issues hindering nanoelectronic integration. In this paper, we employed dielectrophoretic force to manipulate n-type GaN nano- and microwires onto a p-type GaN thin film to form a pristine p-n homojunction. The GaN wires were attracted to the n-type Ohmic metal in a direction parallel to the electric field, which was consistent with our simulation results. Violet electroluminescence emanated from the point of the n-GaN wire in contact with the p-GaN thin film. This p-n homojunction device displayed forward conduction above 6–9 V and current rectifying behavior down to a −20 V reverse bias. The current-voltage characteristics are distinctive of a p-n homojunction formed without deleterious damage or contamination.

Controlled fabrication of gallium nitride nano- and micro-wires by dielectrophoretic force and torque

This paper demonstrates the manipulation of neutral dielectric wires with high aspect ratio by a pulsed electric field. Dielectrophoretic (DEP) force and torque were employed to align the randomly positioned GaN nano- and micro-wires. A simulation of the DEP force alignment process confirmed the experimentally observed dependence on alignment yield to frequency and bias of the electric field. Current–voltage measurements of the GaN micro-wires, aligned by DEP force and torque to pre-patterned metal contacts, confirms that the direct manipulation of micro-sized wire with an electric field oscillated at a frequency of 10 kHz–5 MHz.

Growth and Characterization of Undoped and Mg-Doped GaN Nano- and Micro-Columns by Chemical Vapor Deposition

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