Solar-blind Detection Research Articles

Self-powered solar-blind ultraviolet detectors based on the amorphous boron nitride films

Boron nitride (BN) has been a popular material in the field of ultraviolet detection because of its excellent thermal conductivity, high breakdown field strength, high absorption coefficient, and strong resistance to radiation. However, the harsh preparation conditions of its large-scale single crystal films limit the rapid development of its devices. In this work, amorphous BN films were deposited by the magnetron sputtering technique at a relatively low temperatures. On the basis of the films, the asymmetric Schottky junction solar-blind ultraviolet detectors were fabricated by the Ohmic and Schottky contact, respectively. The maximum responsivity and detectivity of the detectors are 6.4 μA/W and 2.5 × 1010 Jones under 20 V bias and 81.1 μW/cm2 ultraviolet light irradiation, respectively. More importantly, the fabricated asymmetric Schottky junction detector also achieves the stable self-powered characteristics due to the presence of its built-in electric field, and the performances are further improved after the rapid thermal annealing. The prepared BN asymmetric Schottky junction detector can operate without the need for the external power supply, which have many advantages such as simplifying the equipment structure and being able to operate in wireless. This work will provide a new reference for the design of the next generation of independent sustainable detectors.

Excellent Wavelength Selectivity of p-AlGaN/n-Ga2O3 Solar-Blind UVC PD.

Due to the advantages of ultrawide bandgap, chemical stability, self-powered, and low cost, gallium oxide (Ga2O3) based photodetectors (PDs) are considered as one of the most promising solar-blind ultraviolet PDs, having garnered significant attention in fields such as missile warning and flame arc detection. High selective ratios and excellent responsivity are important to reduce the false alarm rate in solar-blind detection. However, due to the lack of p-type Ga2O3, existing Ga2O3-based PN PDs utilized heterostructures with narrower bandgap p-type semiconductors (e.g., p-GaN, p-SiC, etc.), inducing poor selective ratios with visible light and ultraviolet-A/B (UVA/B). Therefore, a high Al content AlGaN was used in this study to form a p-AlGaN/n-Ga2O3 solar-blind ultraviolet-C (UVC) PD. Since the bandgap of p-AlGaN aligned with the UVC region, the device exhibited exceptionally high selective ratios with R247nm/R360nm = 3.71 × 105 and R247nm/R300nm = 1.47 × 105 at 0 V, which surpassed the reported Ga2O3-based PN PDs. The formation of the type-II heterojunction facilitated the effective separation and transport of photogenerated carriers, resulting in high responsivity (0.36 A/W) under zero bias. Overall, the high selective ratios and high responsivity of the p-AlGaN/n-Ga2O3 PD in this paper provided a reliable pathway for self-powered solar-blind PDs with a low false alarm rate.

Balancing Carrier Dynamics in Oxygen-Vacancy-Tuned Amorphous Ga2O3 Thin-Film Self-Powered Photoelectrochemical-Type Solar-Blind Photodetector Arrays for Underwater Imaging.

Underwater imaging technology plays a pivotal role in marine exploration and reconnaissance, necessitating photodetectors (PDs) with high responsivity, fast response speed, and low preparation costs. This study presents the synergistic optimization of responsivity and response speed in self-powered photoelectrochemical (PEC)-type photodetector arrays based on oxygen-vacancy-tuned amorphous gallium oxide (a-Ga2O3) thin films, specifically designed for solar-blind underwater detection. Utilizing a low-cost one-step sputtering process with controlled oxygen flow, a-Ga2O3 thin films with varying oxygen vacancy (VO) concentrations are fabricated. By balancing the trade-offs among electrocatalytic reactions, charge transfer, carrier recombination, and trapping, both the responsivity and response speed of a-Ga2O3-based self-powered PEC-PDs are simultaneously improved. Consequently, the optimized PEC-PDs demonstrated exceptional performance, achieving a responsivity of 33.75mA W-1 and response times of 12.8ms (rise) and 31.3ms (decay), outperforming the vast majority of similar devices. Furthermore, a pronounced positive correlation between anomalous transient photocurrent spikes and the concentration of VO defects is observed, offering compelling evidence for VO-mediated indirect recombination. Finally, the proof-of-concept solar-blind underwater imaging system, utilizing an array of self-powered PEC-PDs, demonstrated clear imaging capabilities in seawater. This work provides valuable insight into the potential for developing cost-effective, high-performance a-Ga2O3 thin-film-based PEC-PDs for advanced underwater imaging technology.

β-Ga2O3 Nanoribbon with Ultra-High Solar-Blind Ultraviolet Polarization Ratio.

Solar-blind ultraviolet (UV) detection plays a critical role in imaging and communication due to its low-noise background, high signal-to-noise ratio, and strong anti-interference capabilities. Detecting the polarization state of UV light can enhance image information and expand the communication dimension. Although polarization detection is explored in visible and infrared light, and applied in fields such as astrophysics and submarine seismic wave detection, solar-blind UV polarization detection remains largely unreported. This is primarily due to the challenge of creating UV polarizers with high transmittance, high extinction ratio, and strong resistance to UV radiation. In this study, it is discovered that the space symmetry breaking of the β-Ga2O3's b-c plane results in a significant optical absorption dichroic ratio. Leveraging β-Ga2O3's high solar-blind UV response, a lensless solar-blind UV polarization-sensitive photodetector, circumventing the challenges associated with solar-blind UV polarizers is designed. This photodetector exhibits an exceptionally high intrinsic polarization ratio under 254nm linearly polarized light, approximately two orders of magnitude higher than other reported nanomaterial-based polarization-sensitive photodetectors. Additionally, it demonstrates significant advantages in solar-blind UV imaging and light communication. This work introduces a novel strategy for solar-blind ultraviolet polarization detection and offers a promising approach for solar-blind light communication.

Highly sensitive full solar-blind ultraviolet spectrum detection and imaging based on PdSe2/Ga2O3 vdW heterojunction.

Solar-blind ultraviolet (UV) photodetectors are in great demand for both military and civilian applications. Here, we have successfully demonstrated the synthesis of the Sn-doped Ga2O3 films with controllable bandgaps to construct PdSe2/Ga2O3 van der Waals (vdW) heterojunctions achieving highly sensitive full solar-blind UV spectrum detection. The assembled device demonstrates a full solar-blind UV spectral self-powered response, with a large responsivity of 123.5 mA/W, a high specific detectivity of 1.63 × 1013 Jones, and a rapid response time of 0.15/2.3 ms. Importantly, an outstanding solar-blind UV imaging application based on an integrated PdSe2/Ga2O3 device array has been demonstrated. Our work paves a feasible path toward achieving highly sensitive solar-blind UV detecting and imaging based on wide-bandgap Ga2O3 films.

Highly sensitive Ga2O3 MSM solar-blind UV photodetector with impact ionization gain.

In this study, a (400) crystal-oriented β-Ga2O3 thin film with a thickness of approximately 400 nm was grown on a c-plane sapphire substrate using atomic layer deposition. Schottky contact-type metal-semiconductor-metal solar-blind ultraviolet detectors with an Au/Ni/Ga2O3/Ni/Au structure were fabricated on the epitaxial thin films. The Schottky barrier height is about 1.1 eV. The device exhibited a high responsivity of up to 800 A/W, and a detectivity of 6 × 1014 Jones while maintaining a relatively fast response speed with a rise time of 4 ms and a fall time of 12 ms. The photo-to-dark current ratio was greater than 103, and the external quantum efficiency exceeded 103, indicating a significant gain in the device. Through the analysis of TCAD simulation and experimental results, it is determined that the impact ionization at the edge of the MSM electrode and channel contact is the main source of gain. Barrier tunneling effects and the photoconductive effect due to different carrier mobilities were not the primary reasons for the gain.

Carbon-doped ZnO thin films: A transparent conductive oxide for application in solar-blind photodetectors

Transparent conductive oxide (TCO) films are crucial in optoelectronic devices, such as photodetectors, due to their unique blend of transparency and electrical conductivity. ZnO is a top choice for TCOs owing to its excellent properties, non-toxicity, and cost-effectiveness. In this work, we explore the potential of carbon doping to enhance the electrical properties of ZnO films for transparent conductive applications. Our findings reveal that C-doped ZnO (ZnO:C) films retain the pristine high quality and surface morphology despite an increase in defects with higher C doping. Notably, C doping does not compromise the visible light transmittance of ZnO films, while inducing a gradual increase in optical bandgap, indicative of the typical Burstein–Moss effect. As carbon doping increases, the ZnO:C films exhibit improved carrier concentration, lower resistivity, and sustained high mobility, achieving optimal performance with an electron concentration of 3.73 × 1019 cm−3, resistivity of 3.69 × 10−3 Ω cm, and mobility of 46.08 cm2 V−1 s−1. Finally, we utilized ZnO:C films as a transparent electrode material in ε-Ga2O3-based photodetector, achieving the development of transparent device and attaining high-performance solar-blind detection capabilities. This work provides a strategy for developing a transparent conductive oxide, with ZnO:C emerging as a promising rival to IIIA-doped ZnO for optoelectronic applications.

Mica-based β-Ga2O3 photodetector: Enabling solar-blind deep-ultraviolet detection with flexibility and transparency

Flexible, transparent solar-blind deep-ultraviolet photodetectors (SBPDs) based on Ga2O3 are gaining momentum for a wide range of future military and civilian applications. However, the fabrication of flexible, transparent SBPDs based on β-Ga2O3 faces challenges due to the inability of commonly used polymer substrates to withstand the high temperatures needed for growth. In this study, the challenge was addressed by producing highly transparent β-phase Ga2O3 thin films on mica substrates using rf magnetron sputtering and annealing techniques. Subsequently, flexible and transparent SBPDs were developed utilizing a metal-semiconductor-metal (MSM) configuration, combining the β-Ga2O3 thin films with an aluminum-doped zinc oxide (AZO) transparent conductive layer. The device with full transparency to visible light revealed a remarkable responsivity of 1.25 A/W and rapid photoresponse rates of 0.18/0.06 s under 254 nm illumination, placing their performance at the forefront among β-Ga2O3-based flexible SBPDs. Notably, even after undergoing numerous mechanical bending tests at varying diameters and cycling counts, the device maintained consistent stability across all performance parameters. This study highlights the potential of mica-based β-Ga2O3 photodetectors for enabling flexible and transparent solar-blind deep-ultraviolet detection.

Performance enhancement of solar-blind UV photodetector by doping silicon in β-Ga2O3 thin films prepared using radio frequency magnetron sputtering

Si-doped β-Ga2O3 thin films were prepared on c-plane (001) sapphire substrates by radio frequency magnetron sputtering, and then annealed at 800 °C under Ar atmosphere for 1 h. Finally, Metal-Semiconductor-Metal type solar-blind UV photodetectors were prepared using the annealed β-Ga2O3 films. The structure, composition, optical properties and photoelectric detection performance of the films were studied using XRD, EDS, UV–Vis, PL spectroscopy and Keithley-4200 system. Results show that after silicon doping, the preferred orientation of the β-Ga2O3 film varies from (−201) to (200) and (201) crystal planes. EDX and XPS results show that 2.34 at% silicon was doped into Ga2O3 films by substituting Ga atoms. Both XPS and PL results show a decline of defect concentration within the Si-doped films, including oxygen vacancy. Si-doped β-Ga2O3 films exhibit enhanced solar-blind detection performance, with lower dark current (32.2 × 10−12 A) under 15 V bias, higher light-to-dark current ratio (3.2 × 104), higher light power density of 2.4 μW/cm2, and shorter response time. The resultant responsivity, detectivity, and external quantum efficiency are 1.146A/W, 7.14 × 1011Jones, and 5.605 %, respectively, more than one order of magnitude higher than the undoped device. This work indicates that Si is an effective n-type dopant for improving the detection performance of β-Ga2O3 film based solar-blind UV photodetectors.

Heterojunction polarization enhancement and shielding for AlGaN-based solar-blind ultraviolet avalanche detectors.

AlGaN-based solar-blind ultraviolet avalanche detectors have huge potentials in the fields of corona discharge monitoring, biological imaging, etc. Here, we study the impact of the heterojunction polarization-related effects on the AlGaN-based solar-blind ultraviolet avalanche detectors. Our work confirms that the polarization heterojunction is beneficial to reducing avalanche bias and lifting avalanche gain by improving the electric field in the depletion region, while the polarization-induced fixed charges will lead to a redistribution of the electrons, in turn shielding the charges and weakening the electric field enhancement effect. This shielding effect will need external bias to eliminate, and that is why the polarization heterojunction cannot work at relatively low bias but has an enhancement effect at high bias. Controlling the doping level between the hetero-interface can affect the shielding effect. An unintentionally doped polarization heterojunction can effectively reduce the shielding effect, thus reducing the avalanche bias. The conclusions also hold true for the negative polarization regime. We believe our findings can provide some useful insights for the design of the AlGaN-based solar-blind ultraviolet detectors.

Synaptic properties of GaOx-based memristor with amorphous GaOx deposited by RF magnetic sputtering

GaOx devices have been extensively explored for applications such as power devices and solar blind detectors, based on their wide bandgap. In this study, we investigated the synaptic properties of the amorphous gallium oxide (a-GaOx)- based memristor with a W/WOx/a-GaOx/ITO structure, in which a-GaOx are deposited by RF magnetic sputtering at ambient temperature. The structure and components of a-GaOx are characterized by XRD, XPS, SEM, and EDS. The electrical test indicates that W/WOx/a-GaOx is ohmic due to the thin WOx layer with a high concentration of oxygen vacancies. Consequently, the synaptic characteristics of the W/WOx/a-GaOx/ITO memristor depend on both the a-GaOx layer itself and the a-GaOx/ITO junction. The fitting results indicate that the a-GaOx/ITO junction is Schottky with unidirectional conductive properties. However, the elevated defect density results in a larger current for the reverse-biased a-GaOx/ITO junction. Moreover, adjusting the thickness of a-GaOx allows the device to achieve almost symmetrical forward and reverse currents. We have successfully observed typical synaptic characteristics in W/WOx/a-GaOx/ITO when stimulated by consecutive spike signals. Clearly, through careful design considerations regarding the structure and parameters, we have realized superior synaptic performance in a-GaOx-based memristors. This achievement shows that amorphous GaOx has great potential applications in neuromorphic computation chips for artificial intelligence or the Internet of Things in the future.

Sputtered Sn-doped Ga2O3 films under balance controlled of energy supply and ion bombardment for solar-blind detection application

The characteristics of amorphous Sn-doped Ga2O3 films deposited using radio frequency magnetron sputtering at room temperature under different sputter powers have been demonstrated. A balance mechanism of energy supply and ion bombardment controlled by sputter power has been found during the deposition. The increasing growth rate as power can be due to the increased yield sputtering species indicated by an in situ optical emission spectroscopy. As the power increases to 700 W, an obvious change from discrete nanoparticles to flat-continuous film can be observed because of sufficient energy supply for oxidation reaction, which leads to the maximum ratio of lattice oxygen and Sn4+ indicating the optimal film quality and conductive property. However, a non-negligible high energy ion bombardment presented at 900 W leads to the degraded film quality. The influence of sputtering power on Sn-doped Ga2O3 solar-blind photodetectors is demonstrated. It can obtain a good performance with an ultra-low dark current density of 2.2 × 10−11 A/cm2, a substantial light-dark current ratio of 1.08 × 103 and fast rise/decay time of 1.59 s/0.54 s at 700 W. The revelation of the role of sputtering power on the properties of Sn-doped Ga2O3 films may offer an interesting direction for low-cost and high-performance solar-blind photodetectors.

Ultrafast Multifunctional Photodetector Based on the NiAl2O4/4H-SiC Heterojunction.

Solar-blind photodetectors based on wide bandgap semiconductors have recently attracted a lot of interest. Nickel-containing spinel phase oxides, such as NiAl2O4, are stable p-type semiconductors. This paper describes a multifunctional solar-blind photodetector based on a NiAl2O4/4H-SiC heterojunction that utilizes photovoltaic effects. The position sensitivity reaches a value of 1589.7 mV/mm under 405 nm laser illumination, while the relaxation times of vertical photovoltaic (VPV) effect and lateral photovoltaic (LPV) effect under 266 nm laser illumination are only 0.32 and 0.42 μs, respectively. This junction was used to create a space optical communication system with sunlight having little effect on its optoelectronic properties. The ultrafast photovoltaic relaxation time makes NiAl2O4/4H-SiC a promising candidate for self-powered high-performance solar-blind detectors.

High-speed performance self-powered short wave ultraviolet radiation detectors based on κ(ε)-Ga2O3

High-speed solar-blind short wavelength ultraviolet radiation detectors based on κ(ε)-Ga2O3 layers with Pt contacts were demonstrated and their properties were studied in detail. The κ(ε)-Ga2O3 layers were deposited by the halide vapor phase epitaxy on patterned GaN templates with sapphire substrates. The spectral dependencies of the photoelectric properties of structures were analyzed in the wavelength interval 200–370 nm. The maximum photo to dark current ratio, responsivity, detectivity and external quantum efficiency of structures were determined as: 180.86 arb. un., 3.57 A/W, 1.78 × 1012 Hz0.5∙cm∙W−1 and 2193.6%, respectively, at a wavelength of 200 nm and an applied voltage of 1 V. The enhancement of the photoresponse was caused by the decrease in the Schottky barrier at the Pt/κ(ε)−Ga2O3 interface under ultraviolet exposure. The detectors demonstrated could functionalize in self-powered mode due to built-in electric field at the Pt/κ(ε)-Ga2O3 interface. The responsivity and external quantum efficiency of the structures at a wavelength of 254 nm and zero applied voltage were 0.9 mA/W and 0.46%, respectively. The rise and decay times in self-powered mode did not exceed 100 ms.

Electronic transport and optical properties of five different phases (α, β, ε, δ and γ) of Ga2O3: A first-principles study

In the field of power and ultraviolet devices, Ga2O3 becomes an emerging semiconductor due to its large energy bandgap and suitable optical absorption wavelength at solar blind ultraviolet band. In this work, the electronic and optical properties of five Ga2O3 polymorphs are investigated by the first-principles calculations to study their potential in ultraviolet devices. The geometry structures, electronic structure, optical and electronic transport properties of five polymorphs have been investigated through GGA + U approach and deformation potential theory. Based on the deformation potential theory, the anisotropic electron mobility of five Ga2O3 polycrystals is obtained by analyzing the parameters obtained from the first-principles calculation. TCAD simulations using calculation results before show the spectral response of MSM solar-blind detectors based on five polymorphs, and indicating that ε-Ga2O3 is the best candidate material for solar blind UV detector. This work provides theoretical insights for the preparation of different phase gallium oxide materials and devices.

High-performance single crystal diamond pixel photodetector with nanosecond rise time for solar-blind imaging

Solar-blind ultraviolet imaging detector is widely applied in many commercial and military fields, such as missile warning, guidance, ultraviolet communication, biomedical analysis, and police reconnaissance. High-performance pixel photodetector is the core of imaging technology. Therefore, its construction attracts intensive attentions in recent years. In this work, 8 × 8 planar pixels were constructed on high quality single crystal diamond using ultraviolet direct writing lithography. A typical pixel photodetector in metal-semiconductor-metal (MSM) structure achieved outstanding photo-response properties of a low dark current of 10−13–10−12 A at 50 V, a high light-dark current switching ratio over 105), a high responsivity of 22.6 A/W, and a decent specific detectivity of 4.2 × 1014 Jones. Moreover, the detector has a fast response time of 13 ns. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable solar-blind imaging photodetector with high spatial resolution.

Solar-Blind Photodetector Arrays Fabricated by Weaving Strategy.

The quest for solar-blind photodetectors (SBPDs) with exceptional optoelectronic properties for imaging applications has prompted the investigation of SBPD arrays. Ga2O3, characterized by its ultrawide bandgap and low growth cost, has emerged as a promising material for solar-blind detection. In this study, SBPD arrays were fabricated by weaving Sn-doped β-Ga2O3 microbelts (MBs). These MBs, which have a conductive core surrounded by a high-resistivity depletion surface layer resulting from the segregation of Sn and oxygen, are woven into a grid structure. Each intersection of the MBs functions as a photodetector pixel, with the intersecting MBs serving as the output electrodes of the pixel. This design simplifies the readout circuit for the photodetector array. The solar-blind photodetector array demonstrates superior solar-blind detection performance, including a dark current of 0.5 pA, a response time of 38.8 μs, a light/dark current ratio of 108, and a responsivity of 300 A/W. This research may provide a feasible strategy for the fabrication of photodetector arrays, thus pushing forward the application of photodetectors in imaging.

Transmission enhancement in coupled nanohole and nanodisk arrays for solar blind UV filter

Extraordinary optical transmission (EOT) based on metallic nanohole array has great potential for optical filtering, owing to its spectral selectivity and structure-dependent tunability. However the transmittance of EOT is relatively low owing to the large loss of the metal film, particularly in the UV waveband. Herein, we propose a high transmission narrowband ultraviolet filter based on aluminum compound nanostructures on a UV-grade fused silica substrate. These compound nanostructures are consisted of periodic nanodisk and nanohole arrays with the same period in a staggered rectangular arrangement. Numerical simulations using the finite-difference time-domain (FDTD) method have shown that the compound structures exhibit high transmittance of over 70% and a narrower bandwidth of less than 50 nm in the 200–300 nm spectral region compared with the conventionally EOT of pure metallic nanohole arrays. Moreover, a broad suppression in the wavelength ranges of 300 to 1100 nm was achieved. The enhanced performance is attributed to the coupling between the surface plasmon polariton (SPP) of nanohole arrays and the localized surface plasmon resonance (LSPR) of nanodisk arrays. The compound coupled nanostructures can be used in solar-blind ultraviolet detectors and the enhancement mechanism has potential for use in other spectral regions.

Solar-blind ultraviolet photodetector based on Nb2C/β-Ga2O3 heterojunction

β-Ga2O3 has been widely investigated for its stability and thermochemical properties. However, the preparation of β-Ga2O3 thin films requires complex growth techniques and high growth temperatures, and this has hindered the application of β-Ga2O3 thin films. In this study, β-Ga2O3 thin films with good crystalline quality were prepared using a green method, and an ultraviolet (UV) detector based on β-Ga2O3 with a photocurrent of 2.54 × 10–6 A and a dark current of 1.19 × 10–8 A has been developed. Two-dimensional materials have become premium materials for applications in optoelectronic devices due to their high conductivity. Here, we use the suitable energy band structure between Nb2C and Ga2O3 to create a high carrier migration barrier, which reduces the dark current of the device by an order of magnitude. In addition, the device exhibits solar-blind detection, high responsiveness (28 A W−1) and good stability. Thus, the Nb2C/β-Ga2O3 heterojunction is expected to be one of the promising devices in the field of UV photoelectric detection.

Surface chemical composition and HRTEM analysis of heteroepitaxial β-Ga2O3 films grown by MOCVD

β gallium oxide (β-Ga2O3) is an ultrawide bandgap semiconductor with great potential for solar-blind ultraviolet detection, power devices, and gas sensing. However, the understanding of the surface properties of β-Ga2O3 remains insufficient. Here, epitaxial growth of β-Ga2O3 films was carried by metal–organic chemical vapor deposition (MOCVD) on sapphire substrates. The surface chemical composition, surface layer crystalline properties, and surface morphology of the β-Ga2O3 films were discussed and analyzed in detail. By comparing the atomic ratios of O/Ga, the surface morphology, and the crystalline properties of the films, we attribute the component of O 1s with the binding energy around 531.8 eV to surface lattice O atoms. Moreover, the one-dimensional defects inside the surface layers and the near-interface regions of the films were observed at atomic scale by high resolution transmission electron microscopy (HRTEM). By comparing the lattice fringes of different facets, the geometric phase uniformity, and the distribution of strain, we found that the crystalline quality of the surface layers is much higher than the near-interface regions.