GaN Thin Films Research Articles

Light-stimulated artificial synapses based on Si-doped GaN thin films

A simple, two-terminated, light-stimulated synaptic device based on GaN thin films was reported, which enables multiple functionalities of biological synapses including the transition from short-term to long-term memory, and cognitive behavior.

Disorder Induced in Gan Thin Films by 200 Mev Silver Ions

Disorder Induced in Gan Thin Films by 200 Mev Silver Ions

Integration of H2V3O8 nanowires and a GaN thin film for self-powered UV photodetectors.

H2V3O8/GaN n-n heterojunction ultraviolet photodetectors are fabricated via a facile dip-coating method. The Schottky junction between the GaN and H2V3O8 builds a built-in electric field to achieve the self-powered phenomenon. The photodetector presents a high photocurrent (0.23 μA) and a fast response speed (less than 0.3 s) at 0 V bias and under 365 nm light illumination (24.50 mW cm-2). Furthermore, the photocurrent increases steadily as the light intensity increases from 0.53 to 24.50 mW cm-2. The H2V3O8/GaN heterojunction holds great potential to realize high-performance hybrid PDs.

PECVD-prepared high-quality GaN films and their photoresponse properties

In this study, the high-quality GaN films are prepared by a simple, green and low-cost plasma enhanced chemical vapor deposition (PECVD) method at 950 ℃, with Ga<sub>2</sub>O<sub>3</sub> and N<sub>2</sub> serving as a gallium source and a nitrogen source, respectively. In order to improve the crystal quality of GaN films and ascertain the photoresponse mechanism of GaN films, the effect of the preparation temperature of GaN buffer layer on the crystal quality and photoelectric properties of GaN thin films are investigated. It is indicated that with the increase of the buffer temperature of GaN films, the crystal quality of GaN films first increases and then decreases, and the highest crystal quality is obtained at 875 ℃. When buffer layer temperature is 875 ℃, the calculated total dislocation density is 9.74 × 10<sup>9</sup> cm<sup>–2</sup>, and the carrier mobility is 0.713 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>. The crystal quality of GaN film after being annealed is improved. The total dislocation density of GaN film decreases to 7.38 × 10<sup>9</sup> cm<sup>–2</sup>, and the carrier mobility increases to 43.5 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>. The UV-Vis absorption spectrum results indicate that the optical band gap of GaN film is 3.35 eV. The scanning electron microscope (SEM) results indicate that GaN film (buffer layer temperature is 875 ℃) has smooth surface and compact structure. The Hall and X-ray photoelectron spectroscopy (XPS) results indicate that there are N vacancies, Ga vacancies or O doping in the GaN film, which act as deep level to capture photogenerated electrons and holes. With the bias increasing, the photoresponsivity of the GaN film photodetector gradually increases and then reaches a saturation value. This is due to the deep levels produced by vacancy or O doping. In addition, photocurrent response and recovery of GaN film are slow, which is also due to the deep levels formed by vacancy or O doping. At 5-V bias, the photoresponsivity of GaN film is 0.2 A/W, rise time is 15.4 s, and fall time is 24 s. Therefore, the high-quality GaN film prepared by the proposed green and low-cost PECVD method present a strong potential application in ultraviolet photodetector. The PECVD method developed by us provides a feasible way of preparing high-quality GaN films, and the understanding of the photoresponse mechanism of GaN films provides a theoretical basis for the wide application of GaN films.

Effect of Different Substrates on Material Properties of Cubic Gan Thin Films Grown by Lp-Mocvd Method

Effect of Different Substrates on Material Properties of Cubic Gan Thin Films Grown by Lp-Mocvd Method

The Effect of Al-Doping and A- Irradiation on the Electrical Properties of Gan Thin Films Grown by Electrodeposition

The Effect of Al-Doping and A- Irradiation on the Electrical Properties of Gan Thin Films Grown by Electrodeposition

Effects of post-annealing on GaN thin films growth using RF magnetron sputtering

Effects of post-annealing on GaN thin films growth using RF magnetron sputtering

Low-Temperature Growth of Crystalline Gan Thin Films on Quartz Substrates with Sharp Interfaces

Low-Temperature Growth of Crystalline Gan Thin Films on Quartz Substrates with Sharp Interfaces

Narrowband near-ultraviolet photodetector fabricated from porous GaN/CuZnS heterojunction

Narrowband photodetection systems are widely used in fluorescence detection, artificial vision and other fields. In order to realize the narrow spectral detection of special band, it is traditionally necessary to integrate broadband detectors with optical filters. However, with the development of detection technology, higher requirements have also been placed on the power consumption, size, and cost of the detection system, and the applications of traditional narrowband photodetectors with complex structures and high costs are limited. Thus, a filterless, narrowband near-ultraviolet photodetector based on a porous GaN/CuZnS heterojunction is demonstrated. The porous GaN thin films with low defect density and CuZnS thin films with high hole conductivity are fabricated by photoelectrochemical etching and water bath growth methods, respectively, and the porous GaN/CuZnS heterojunction near-ultraviolet photodetectors are thus fabricated. Benefiting from the porous structure of GaN and the optical filtering effect of CuZnS, the photo-dark current ratio of the device exceeds four orders of magnitudes under –2 V bias and 370 nm light illumination; more importantly, the device has an ultra-narrowband near-ultraviolet photoresponse with a full width at half maximum of <8 nm (peak at 370 nm). In addition, the peak responsivity, external quantum efficiency and specific detectivity reach 0.41 A/W, 138.6% and 9.8×10<sup>12</sup> Jones, respectively. These excellent device performances show that the near-ultraviolet photodetectors based on porous GaN/CuZnS heterojunctions have broad application prospects in the field of narrow-spectrum ultraviolet photodetection.

The Mechanism of Charge Flow and Electric Current in Porous GaN Thin Films during Photo Electrochemical Etching

The Mechanism of Charge Flow and Electric Current in Porous GaN Thin Films during Photo Electrochemical Etching

Comparative study on the nanomechanical behavior and physical properties influenced by the epitaxial growth mechanisms of GaN thin films

The effect of carrier gas on nanomechanical properties of GaN thin films grown on (0001) sapphire substrates by metal–organic chemical vapor deposition (MOCVD) process, was studied by Berkovich nanoindentation. GaN/H2 and GaN/N2 films were deposited using hydrogen and nitrogen, as carrier gases, respectively. New method was developed to compute the contact stiffness versus the penetration depth using a single load–displacement curve. It was found that the hardness and Young’s modulus of GaN/H2 are lower than those of GaN/N2. Moreover, pop-in events were revealed for GaN/H2, in contrast for GaN/N2. Fracture was only manifested in the imprint of GaN/N2 due to its low fracture toughness. Besides, it was disclosed the high sensitivity of loading rate only for GaN/H2. The GaN/N2 sample experiences plastic strain relaxation, while GaN/H2 is a highly stressed sample; hence, it has less dislocation density compared to GaN/N2 sample. We demonstrated that the used carrier gas influences on GaN epitaxial growth process, which in return deeply affects the resulting dislocation density and dislocation plasticity mechanisms. These latter, tailor the nanomechanical properties of GaN samples and the indentation-induced deformation behavior.

Temperature dependence of the piezotronic and piezophototronic effects in flexible GaN thin films

Flexible devices operated at a cryogenic temperature are required for significant applications, such as sensors in thermal imaging and infrared and nuclear particle detectors. Hence, in this study, comprehensive temperature dependence was performed on flexible GaN thin films from 225 K to 325 K under 0.0–0.3% strains to investigate the piezotronic and piezophototronic effects. The GaN thin-film device strongly depends on the applied temperature, and the piezotronic effect is enriched by above 360% under 0.3% applied strain at a low chamber temperature. This type of behavior is caused by the increased essential piezocharges at the interface/surface, which results from the less screening effect of the reduced charge carriers in the GaN thin film. To support this behavior, we investigate the piezophototronic effect in a GaN thin film at various temperatures under different strains. The study results will provide an in-depth understanding of the piezotronic and piezo-photonic effects and pave the way for forthcoming device applications in various fields, including human–machine interface, health monitoring, artificial intelligence, and surgical robotic operations.

Strain-induced piezotronic effects in nano-sized GaN thin films

Flexible devices have attracted considerable attention because of their very productive applications in the diverse areas such as healthcare, artificial intelligence, and robotics. Accordingly, in this study, we fabricated a flexible nano-sized GaN thin-film device via a double-transfer method using a laser lift-off process from sapphire with thermal tape and then with carbon tape onto a polycarbonate substrate. With the application of compressive/tensile strains, the flexible nano-sized GaN thin-film device can be mechanically controlled by the piezotronic effect. The device has excellent electromechanical performance with a gauge factor of 2206 at a compressive strain of 0.32%, which is nearly 11.11 times greater than that of a conventional strain-gauge value. Furthermore, the device shows an effective ON condition in the compressive direction and OFF condition in the tensile direction at an applied bias voltage of 0.5 V. The fabricated device has potential for innovative and advanced applications such as human–machine interfaces, biomedical diagnoses, prostheses, intelligently controlled rooms, and active flexible electronics.

Raman tensor determination of transparent uniaxial crystals and their thin films—a-plane GaN as exemplary case

The classical Raman tensor approach does not work for optically anisotropic materials in general. For the transparency regime, this can be circumvented by using an effective Raman tensor that considers the material's birefringence. In the specific case of an uniaxial crystal with in-plane orientation of principal axis, this effective Raman tensor is similar to the classical one, except for an additional phase factor for each tensor element. This phase is dependent on the sample thickness, which is demonstrated here experimentally via polarization resolved Raman scattering of a-plane GaN thin films. The experimental observations coincide very well with our model predictions.

Initial Study of GaN Thin Films for Photocathodes Prepared by Magnetron Sputtering on Copper Substrates

Initial Study of GaN Thin Films for Photocathodes Prepared by Magnetron Sputtering on Copper Substrates

Defect analysis of star defects in GaN thin films grown on HVPE GaN substrates

Defect analysis of star defects in GaN thin films grown on HVPE GaN substrates

GaN thin film: Growth and Characterizations by Magnetron Sputtering

In this article, growth of GaN thin film on low-cost electronic substrate (n-Si) by magnetron sputtering method was reported. Growth parameters of GaN thin film have been studied based on different flow rate of sputtering gasses, chamber pressure, sputtering power, substrate temperature and duty ratio of pulse signals. Characterization techniques such as X-ray diffraction (XRD), micro photoluminescence (µ-PL), raman spectroscopy, transmittance, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were performed to explore the optical and structural properties. XRD studies confirmed the wurtzite structure of grown thin film with the preferentially orientation along (002) plane, it also reveals the effect of growth parameters on the grain size and crystal quality of thin films. E2 (high) and A1 (LO) modes were observed in raman spectrum. Room temperature µ-PL and optical transmittance shows the near band edge (NBE) and sharp transmission edge around ∼3.3 eV relates to the band gap value of GaN structure.

Nanoindentation of AlN, GaN, and AlGaN films grown by HVPE on SiC/Si hybrid substrates

This paper presents an experimental study of structural and mechanical characteristics of thin films of AlN, GaN, and AlGaN grown on hybrid SiC/Si substrates by the method of HVPE. The surface roughness of the films and substrates has been measured. The thickness and molecular composition of the films have been determined by spectral ellipsometry. An analysis of elastic deformation occurring in the films as a result of indentation has been made. The values of hardness and Young’s modulus of the films have been calculated.

Temperature Effect of van der Waals Epitaxial GaN Films on Pulse-Laser-Deposited 2D MoS2 Layer

Van der Waals epitaxial GaN thin films on c-sapphire substrates with a sp2-bonded two-dimensional (2D) MoS2 buffer layer, prepared by pulse laser deposition, were investigated. Low temperature plasma-assisted molecular beam epitaxy (MBE) was successfully employed for the deposition of uniform and ~5 nm GaN thin films on layered 2D MoS2 at different substrate temperatures of 500, 600 and 700 °C, respectively. The surface morphology, surface chemical composition, crystal microstructure, and optical properties of the GaN thin films were identified experimentally by using both in situ and ex situ characterizations. During the MBE growth with a higher substrate temperature, the increased surface migration of atoms contributed to a better formation of the GaN/MoS2 heteroepitaxial structure. Therefore, the crystallinity and optical properties of GaN thin films can obviously be enhanced via the high temperature growth. Likewise, the surface morphology of GaN films can achieve a smoother and more stable chemical composition. Finally, due to the van der Waals bonding, the exfoliation of the heterostructure GaN/MoS2 can also be conducted and investigated by transmission electron microscopy. The largest granular structure with good crystallinity of the GaN thin films can be observed in the case of the high-temperature growth at 700 °C.

Removal of GaN film over AlGaN with inductively coupled BCl3/Ar atomic layer etch

Atomic layer etching (ALE) of thin film GaN (0001) is reported in detail using sequential surface modification by BCl3 adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a reactive ion etching system. The estimated etching rate of GaN is ∼ 0.74 nm/cycle. The GaN is removed from the surface of AlGaN after 135 cycles. To study the mechanism of the etching, the detailed characterization and analyses are carried out, including scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). It is found that in the presence of GaCl x after surface modification by BCl3, the GaCl x disappears after having exposed to low energy Ar plasma, which effectively exhibits the mechanism of atomic layer etch. This technique enables a uniform and reproducible fabrication process for enhancement-mode high electron mobility transistors with a p-GaN gate.