Graphene Interdigital Electrodes for Improving Sensitivity in a Ga2O3:Zn Deep-Ultraviolet Photoconductive Detector

Carbon Micro/Nano Machining toward Miniaturized Device: Structural Engineering, Large-Scale Fabrication, and Performance Optimization

With the rapid development of micro/nano machining, there is an elevated demand for high-performance microdevices with high reliability and low cost. Due to their outstanding electrochemical, optical, electrical, and mechanical performance, carbon materials are extensively utilized in constructing microdevices for energy storage, sensing, and optoelectronics. Carbon micro/nano machining is fundamental in carbon-based intelligent microelectronics, multifunctional integrated microsystems, high-reliability portable/wearable consumer electronics, and portable medical diagnostic systems. Despite numerous reviews on carbon materials, a comprehensive overview is lacking that systematically encapsulates the development of high-performance microdevices based on carbon micro/nano structures, from structural design to manufacturing strategies and specific applications. This review focuses on the latest progress in carbon micro/nano machining toward miniaturized device, including structural engineering, large-scale fabrication, and performance optimization. Especially, the review targets an in-depth evaluation of carbon-based micro energy storage devices, microsensors, microactuators, miniaturized photoresponsive and electromagnetic interference shielding devices. Moreover, it highlights the challenges and opportunities in the large-scale manufacturing of carbon-based microdevices, aiming to spark further exciting research directions and application prospectives.

High-Performance Solar-Blind Photodetector Based on (010)-Plane β-Ga2O3 Thermally Oxidized from Nonpolar (110)-Plane GaN

A high-performance planar structure metal-semiconductor-metal-type solar-blind photodetector (SBPD) was fabricated on the basis of (010)-plane β-Ga2O3 thermally oxidized from nonpolar (110)-plane GaN. A full width at half maximum of 0.486° was achieved for the X-ray rocking curve associated with (020)-plane β-Ga2O3, which is better than most reported results for the heteroepitaxially grown (-201)-plane β-Ga2O3. As a result of the relatively high crystalline quality, a dark current as low as 6.30 × 10-12 A was achieved at 5 V, while the photocurrent reached 1.86 × 10-5 A under 254 nm illumination at 600 μW/cm2. As a result, the photo-to-dark current ratio, specific detectivity, responsivity, and external quantum efficiency were calculated to be 2.95 × 106, 2.39 × 1012 Jones, 3.72 A/W, and 1815%, respectively. Moreover, the SBPD showed excellent repeatability and stability in the time-dependent photoresponse characteristics with fast relaxation time constants for the rise and decay processes of only 0.238 and 0.062 s, respectively. This study provides a promising approach to fabricate the device-level (010)-plane β-Ga2O3 film and a new way for the epitaxial growth of (010)-plane β-Ga2O3 and (110)-plane GaN as mutual substrates.

Enhancing Performance of Ultraviolet C Photodetectors Through Single-Domain Epitaxy of Monoclinic β-Ga2 O3 Films and Tailored Anti-Reflection Coating

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga2 O3 films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga2 O3 films on a hexagonal sapphire substrate. Unlike 3D β-Ga2 O3 films with twin domains, 2D β-Ga2 O3 films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga2 O3 films and the application of ARC for the development of high-performance UVC PDs.

Boron Nitride Nanoribbons Grown by Chemical Vapor Deposition for VUV Applications

The fabrication process of vacuum ultraviolet (VUV) detectors based on traditional semiconductor materials is complex and costly. The new generation of wide-bandgap semiconductor materials greatly reduce the fabrication cost of the entire VUV detector. We use the chemical vapor deposition (CVD) method to grow boron nitride nanoribbons (BNNRs) for VUV detectors. Morphological and compositional characterization of the BNNRs was tested. VUV detector based on BNNRs exhibits strong response to VUV light with wavelengths as short as 185 nm. The photo-dark current ratio (PDCR) of this detector is 272.43, the responsivity is 0.47 nA/W, and the rise time and fall time are 0.3 s and 0.6 s. The response speed is faster than the same type of BN-based VUV detectors. This paper offers more opportunities for high-performance and low-cost VUV detectors made of wide-bandgap semiconductor materials in the future.

Interfacial thermal transport of graphene/β-Ga2O3 heterojunctions: a molecular dynamics study with a self-consistent interatomic potential

Graphene/β-Ga₂O₃ heterojunctions are widely used in high-power and high-frequency devices, for which thermal management is vital to the device operation and life. Here we apply molecular dynamics simulation to calculate the interfacial thermal resistance (ITR) between graphene and β-Ga₂O₃. Based on the rigid ion model, a self-consistent interatomic potential with a set of parameters that can well reproduce the basic physical properties of crystal β-Ga₂O₃ is fitted. Using this potential, the effects of model size, interface type, temperature, vacancy defects and graphene hydrogenation on the ITR of graphene/β-Ga₂O₃ heterojunctions are evaluated. The results show that there is no obvious dependence of ITR on the size of graphene and β-Ga₂O₃. It is reported that the ITR values of the (100), (010) and (001) interfaces are 7.28 ± 0.35 × 10^-8 K m² W^-1, 6.69 ± 0.44 × 10^-8 K m² W^-1 and 5.22 ± 0.35 × 10^-8 K m² W^-1 at 300 K, respectively. Both temperature increase and vacancy defect increase can prompt the energy propagation across graphene/β-Ga₂O₃ interfaces due to the enhancement of phonon coupling. In addition, graphene hydrogenation provides new channels for in-plane and out-of-plane phonon coupling, and thus reduces the ITR between graphene and β-Ga₂O₃. This study provides basic strategies for the thermal design and management of graphene/β-Ga₂O₃ based photoelectric devices.

Synthesis, mechanism and characterization of Urchin-like Ga2O3 microspheres

An effective method without catalyst and template was developed to synthesize a novel micro-/nanostructures of gallium oxide (Ga2O3) for the first time. The urchin-like microspheres with uniformly distributed nanowires were...

Comprehensively Improved Performance of β-Ga2O3 Solar-Blind Photodetector Enabled by a Homojunction with Unique Passivation Mechanisms

Ga₂O₃-based solar-blind photodetectors have been extensively investigated for a wide range of applications. However, to date, a lot of research has focused on optimizing the epitaxial technique or constructing a heterojunction, and studies concerning surface passivation, a key technique in electronic and optoelectronic devices, are severely lacking. Here, we report an ultrasensitive metal-semiconductor-metal photodetector employing a β-Ga₂O₃ homojunction structure realized by low-energy surface fluorine plasma treatment, in which an ultrathin fluorine-doped layer served for surface passivation. Without inserting/capping a foreign layer, this strategy utilized fluorine dopants to both passivate local oxygen vacancies and suppress surface chemisorption. The dual effects have opposite impacts on device current magnitude (by suppressing metal/semiconductor junction leakage and inhibiting surface-chemisorption-induced carrier consumption) but dominate in dark and under illumination, respectively. By means of such unique mechanisms, the simultaneous improvement on dark and photo current characteristics was achieved, leading to the sensitivity enhanced by nearly 1 order of magnitude. Accordingly, the 15 min treated sample exhibited striking competitiveness in terms of comprehensive properties, including a dark current as low as 6 pA, a responsivity of 18.43 A/W, an external quantum efficiency approaching 1 × 10⁴%, a specific detectivity of 2.48 × 10¹⁴ Jones, and a solar-blind/UV rejection ratio close to 1 × 10⁵. Furthermore, the response speed was effectively accelerated because of the reduction on metal/semiconductor interface trap states. Our findings provide a facile, economical, and contamination-free surface passivation technique, which unlocks the potential for comprehensively improving the performance of β-Ga₂O₃ solar-blind metal-semiconductor-metal photodetectors.

Research of nanopore structure of Ga2O3 film in MOCVD for improving the performance of UV photoresponse

Using the mechanism of self-reactive etching between Ga and Ga₂O₃, Ga₂O₃ nanopore films were fabricated. The self-reactive etching effects based on as-grown and annealed Ga₂O₃ films by metal organic chemical vapor deposition were compared. It was found that the nanopore film based on as-grown Ga₂O₃ film has a uniform size, high density and a small diameter. Ultraviolet-visible light reflection spectra and transmission spectra show that the nanopore film could effectively reduce the reflectivity of light and enhance the light absorption. Based on the as-grown Ga₂O₃ film and its nanopore film, metal-semiconductor-metal structure solar blind ultraviolet photodetectors (PD) were fabricated. Under 5 V bias, the light-dark current ratio of the nanopore film PD is about 2.5 × 10² times that of the film PD, the peak responsivity of the nanopore film PD is about 49 times that of the film PD. The rejection ratio is 4.6 × 10³, about 1.15 × 10² times that of the film PD. The nanopore structure effectively increases the surface-volume ratio of film. The photoelectric detection performance and response performance of the nanopore film PD could be significantly enhanced.

High-Performance X-ray Detector Based on Single-Crystal β-Ga2O3:Mg

X-ray detection plays an important role in medical imaging, scientific research, and security inspection. Recently, the β-Ga₂O₃ single-crystal-based X-ray detector has attracted extensive attention due to its excellent intrinsic properties such as good absorption for X-ray photons, a high breakdown electric field, high stability, and low cost. However, developing a high-performance β-Ga₂O₃-based X-ray detector remains a challenge because of the large dark current and the high oxygen vacancy concentration in the crystals. In this paper, we report a high-performance Mg-doped β-Ga₂O₃ single-crystal-based X-ray detector with a sandwich structure. The reduced dark current enables the detector to have a high sensitivity of 338.9 μC Gy^-1 cm^-2 under 50 keV X-ray irradiation with a dose rate of 69.5 μGy/s. The sensitivity is 16-fold higher than that of the commercial amorphous selenium detector. Furthermore, the reduced oxygen vacancy concentration can improve the response speed (<0.2 s) of the detector. The present studies provide a promising method to obtain the high performances for the X-ray detector based on β-Ga₂O₃ single crystals.

High Responsivity and External Quantum Efficiency Photodetectors Based on Solution-Processed Ni-Doped CuO Films

Photodetectors based on p-type metal oxides are still a challenge for optoelectronic device applications. Many effects have been paid to improve their performance and expand their detection range. Here, high-quality Cu_1-xNi_xO (x = 0, 0.2, and 0.4) film photodetectors were prepared by a solution process. The crystal quality, morphology, and grain size of Cu_1-xNi_xO films can be modulated by Ni doping. Among the photodetectors, the Cu_0.8Ni_0.2O photodetector shows the maximum photocurrent value (6 × 10^-7 A) under a 635 nm laser illumination. High responsivity (26.46 A/W) and external quantum efficiency (5176%) are also achieved for the Cu_0.8Ni_0.2O photodetector. This is because the Cu_0.8Ni_0.2O photosensitive layer exhibits high photoconductivity, low surface states, and high crystallization after 20% Ni doping. Compared to the other photodetectors, the Cu_0.8Ni_0.2O photodetector exhibits the optimal response in the near-infrared region, owing to the high absorption coefficient. These findings provide a route to fabricate high-performance and wide-detection range p-type metal oxide photodetectors.

In-plane enhanced epitaxy for step-flow AlN yielding a high-performance vacuum-ultraviolet photovoltaic detector

In-plane enhanced epitaxy provides reference for the preparation of high-quality AlN and development of VUV photodetectors..

Ultra-Robust Deep-UV Photovoltaic Detector Based on Graphene/(AlGa)2O3/GaN with High-Performance in Temperature Fluctuations

A strategy of adopting Ga₂O₃ alloyed with Al element to reduce the oxygen vacancy defect density and enhance the interface barrier height of Ga₂O₃ heterojunction is proposed to fabricate deep-UV photovoltaic detectors with high thermal stability, high photoresponsivity, and fast response speed. Here, a graphene/(AlGa)₂O₃/GaN device with a photoresponsivity of ∼20 mA/W, a rise time of ∼2 μs, and a decay time of ∼10 ms is presented at 0 V bias. At the working temperature of 453 K, the device still exhibits a photo-to-dark current ratio (PDCR) of ∼1.8 × 10³, which is 1-2 orders of magnitude higher than that of the reported high-temperature deep-UV film detectors. By comparing the formation energy of oxygen vacancy defects and the interface barrier height of the heterojunction at different temperatures in graphene/Ga₂O₃/GaN and graphene/(AlGa)₂O₃/GaN systems, the strategy of synthesizing (AlGa)₂O₃ ternary composite alloy is proved to be reliable for fabricating high-performance deep-UV photovoltaic detectors. The method proposed in this paper can provide reference for the preparation of deep-UV photovoltaic detectors with high photoresponsivity and thermal stability in the future.