Solar-blind Photodetectors Research Articles

Self-Powered Solar-Blind Photodetector With Low Dark Current and Ultrahigh On/Off Ratio Based on Vertically Aligned Si/SiC Nanowire Arrays p-n Heterojunction

Self-Powered Solar-Blind Photodetector With Low Dark Current and Ultrahigh On/Off Ratio Based on Vertically Aligned Si/SiC Nanowire Arrays p-n Heterojunction

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.

Highly-Polarized Solar-Blind Ultraviolet Organic Photodetectors.

Developing high-performance polarization-sensitive ultraviolet photodetectors is crucial for their application in military remote sensing, detection, bio-inspired navigation, and machine vision. However, the significant absorption in the visible light range severely limits the application of polarization-sensitive ultraviolet photodetectors, such as high-quality anti-interference imaging. Here, based on a wide-bandgap organic semiconductor single crystal (trans-1,2-bis(5-phenyldithieno[2,3-b:3',2'-d]thiophen-2-yl)ethene, BPTTE), high-performance polarization-sensitive solar-blind ultraviolet photodetectors with a dichroic ratio close to 4.26 are demonstrated. The strong anisotropy of 2D grown BPTTE single crystals in molecular vibration and optical absorption is characterized by various techniques. Under voltage modulation, stable and efficient detection of polarized light is demonstrated, attributed to the intrinsic anisotropy of transition dipole moment in the bc crystal plane, rather than other factors. Finally, high-contrast polarimetric imaging and anti-interference imaging are successfully demonstrated based on BPTTE single crystal photodetectors, highlighting the potential of organic semiconductors for polarization-sensitive solar-blind ultraviolet photodetectors.

Unveiling the orientation growth mechanism and solar-blind response performance of β-Ga2O3 (100) film on SiC substrate with AlN buffer layer

Optimizing the orientation of β-Ga2O3 has emerged as an effective strategy to design high-performance β-Ga2O3 device, but the orientation growth mechanism and approach have not been revealed yet. Herein, by employing AlN buffer layer, the highly preferred orientation of β-Ga2O3 (100) film rather than (-201) film is realized on 4H-SiC substrate at low sputtering power and temperature. Because β-Ga2O3 (100) film exhibits a slower growth speed than (-201) film, the former possesses the higher dangling bond density and the lower nucleation energy, and a large conversion barrier exists between these two orientations. Moreover, the AlN buffer layer can suppress the surface oxidation of the 4H-SiC substrate and eliminate the strain of β-Ga2O3 (100) film, which further reduces the nucleation energy and enlarges the conversion barrier. Meanwhile, the AlN buffer layer can increase the oxygen vacancy formation energy and decrease the oxygen vacancy concentration of β-Ga2O3 (100) film. Consequently, the solar-blind photodetector based on the oriented film exhibits the outstanding detectivity of 1.22 × 1012 Jones and photo-to-dark current ratio of 1.11 × 105, which are the highest among the reported β-Ga2O3 solar-blind photodetector on the SiC substrate. Our results offer in-depth insights into the preferred orientation growth mechanism, and provide an effective way to design high-quality β-Ga2O3 (100) orientation film and high-performance solar-blind photodetector.

Recent Progress in Solar-Blind Photodetectors Based on Ultrawide Bandgap Semiconductors.

Ultrawide bandgap (UWBG) semiconductors, including Ga2O3, diamond, Al x Ga1-x N/AlN, featuring bandgaps greater than 4.4 eV, hold significant promise for solar-blind ultraviolet photodetection, with applications spanning in environmental monitoring, chemical/biological analysis, industrial processes, and military technologies. Over recent decades, substantial strides in synthesizing high-quality UWBG semiconductors have facilitated the development of diverse high-performance solar-blind photodetectors (SBPDs). This review comprehensively examines recent advancements in UWBG semiconductor-based SBPDs across various device architectures, encompassing photoconductors, metal-semiconductor-metal photodetectors, Schottky photodiodes, p-n (p-i-n) photodiodes, phototransistors, etc., with a systematic introduction and discussion of their operational principles. The current state of device performance for SBPDs employing these UWBG semiconductors is evaluated across different device configurations. Finally, this review outlines key challenges to be addressed, aiming to steer future research endeavors in this critical domain.

Vertically Graded Oxygen Vacancies in Amorphous Ga2O3 for Offsetting the Conventional Trade-Off between Photoresponse and Response Time in Solar-Blind Photodetectors

Vertically Graded Oxygen Vacancies in Amorphous Ga₂O₃ for Offsetting the Conventional Trade-Off between Photoresponse and Response Time in Solar-Blind Photodetectors

Superior performance of ZnGaO solar-blind photodetectors by Implementing TFT structure and tunable ZnO cycle ratio

In this study, plasma enhanced atomic layer deposition was used to prepare ZnGaO thin films with different ZnO cycle ratios from 0 % to 50 %, which were employed to fabricate the MSM-type and TFT-type solar-blind photodetector. The properties of the films and the performance of the solar blind photodetector are greatly affected by the ZnO cycle ratio. Appropriate Zn doping content decreases the ratio of oxygen vacancies and Zn interstitials in Ga2O3, while excessive Zn doping degrades the quality of the film. Compared to MSM-type photodetector, an obviously improved performance of ZnGaO TFT-type photodetector has been observed due to its self-amplified photocurrent and the reduced dark current controlled by gate voltage. At a ZnO cycle ratio of 40 %, a superior performance of TFT-type solar-blind photodetector with an ultra-low dark current ∼4.5 × 10−13 A, an excellent light switching ratio ∼2.2 × 107, and an outstandingly high sensitivity ∼34.31 A/W has been obtained. These results demonstrate that the incorporation of Zn dopants can effectively modulate the performance of Ga2O3 TFT-type photodetector providing a great perspective for cost-effective and high-performance solar-blind PDs.

Solar blind avalanche photodetector based on a n-β-Ga2O3/n-Si heterojunction via an introduction of AlN buffer layer for interface lattice and band Engineering

The ultrawide-band gap semiconductor Ga2O3 as a photodetector heteroepitaxially grown on Si is expected to be widely used for weak solar-blind signal detections because the optical filters typically used in Si-based UV detectors can be avoided. Photodetectors fabricated from Ga2O3/Si are promising for multi-color detection (Ga2O3-based for UV and Si-based for visible/IR) and are more compatible with traditional Si-based electronic circuits. This paper proposes an n-type semiconductor-barrier-n-type semiconductor (n/B/n) with a unipolar barrier β-Ga2O3/AlN/n-Si heterostructure as a solar-blind avalanche photodetector. Introducing the AlN buffer layer eliminates the native amorphous SiOx layer, reduces lattice mismatch between β-Ga2O3 and Si, and improves the quality of β-Ga2O3 crystallization. Embedding AlN increases the conduction band shift of β-Ga2O3/Si, limits electron migration, reduces device dark current, and increases the reverse breakdown voltage. The β-Ga2O3/AlN (150 nm)/n-Si heterostructure has a high responsivity of 131.3 A/W with a detectivity of 2.9 × 1015 Jones, and an ultrahigh UV/visible (Rpeak/R400nm) rejection ratio of 5.2 × 105 at −55 V. The avalanche gain can also reach 2.7 × 104 at an 85 V reverse bias. This work provides an effective strategy for constructing a high-performance avalanche solar-blind-UV/visible/IR as a multi-color photodetector on one “chip” of a Si-based integrated circuit.

Enhanced Performance of Self-Powered Solar-Blind Deep UV Photodetectors Based on ZnGa2O4/Ga2O3 Heterojunctions

Enhanced Performance of Self-Powered Solar-Blind Deep UV Photodetectors Based on ZnGa₂O₄/Ga₂O₃ Heterojunctions

MgSnO3 epitaxial thin films for solar-blind photodetection: Fabrication and properties

In alkaline earth stannates, MgSnO3 has low density, high specific strength and wide bandgap (∼4.0 eV), which is a particularly promising semiconductor material. However, the lack of single crystal film limits the application of such materials in photoelectric devices. Here, high-quality MgSnO3 epitaxial film was grown on SrTiO3 substrate by pulsed laser deposition (PLD). The film grown under an oxygen pressure of 5 Pa at 900 °C presented the best crystal quality, which has high transmittance (>93 %) and wide bandgap (3.94 eV). The in-plane and out-of-plane epitaxial relationships between the film and substrate are MgSnO3[1 1‾ 00] ⎜⎜SrTiO3[1 1‾ 0] and MgSnO3(0001) ⎜⎜SrTiO3(111), respectively. Due to the lower formation energy of Mg vacancies compared to Sn vacancies, the Mg/Sn molar ratio in the film is less than 1, increasing with the oxygen pressure rising during the film. For the solar-blind photodetector based on 10 Pa sample, the device presents a photo-responsivity of 3.76 × 10−3 A ∙ W−1 and a fast speed of photoresponse (<0.05 s). The excellent performance exhibited by single crystal thin films will undoubtedly promote the development of MgSnO3 based single crystal devices.

Photoelectrochemical properties of self-powered corundum-structured Ga2O3 nanorod array/fluorine-doped SnO2 photodetectors modulated by precursor concentrations

Herein, corundum-structured Ga2O3 (α-Ga2O3) nanorod array/fluorine-doped SnO2 (FTO) structures have been fabricated by hydrothermal and thermal annealing processes with different precursor concentrations from 0.01 to 0.06 M. The diameter and length of the nanorod arrays are much larger with increasing precursor concentrations due to more nucleation sites and precursor ions participating in the reaction procedures. The optical bandgap decreases from 4.75 to 4.47 eV because of the tensile stress relieving with increasing the precursor concentrations. Based on self-powered photoelectrochemical (PEC) photodetectors, the peak responsivity is improved from ∼0.33 mA W−1 for 0.06 M to ∼1.51 mA W−1 for 0.02 M. Schottky junctions can be formed in PEC cells. More photogenerated carriers can be produced in wider depletion region. From Mott–Schottky plots, the depletion regions become much wider with decreasing the precursor concentrations. Therefore, the enhance responsivity is owing to the wider depletion regions. Due to the reduced possibility of photogenerated holes captured by traps ascribed from fewer green and yellow luminescence defects, smaller charge transfer resistance, and shorter transportation route, the decay time becomes much faster through decreasing the precursor concentrations. Compared with the other self-powered α-Ga2O3-nanorod-array-based PEC photodetectors, it shows the fastest response time (decay time of 0.005 s/0.026 s) simply modulated by precursor concentrations for the first time without employing complex precursors, seed layers or special device designs. Compared with other high-responsivity monoclinic Ga2O3 (β-Ga2O3) self-powered photodetectors, our devices also show comparable response speed with simple control and design. This work provides the realization of fast-speed self-powered Ga2O3 based solar-blind ultraviolet photodetectors by simple modulation processes and design, which is a significant guidance for their applications in warnings, imaging, computing, communication and logic circuit, in the future.

A Solar-Blind Ultraviolet Photodetector with Self-Biasing Capability, Controlled by Surface Potential based on GaN Hexagonal Nano-Spikes

In recent years, there’s been growing interest in developing solar-blind self-bias ultraviolet photodetectors for uses like monitoring extreme heat, enhancing security, and improving communications. Gallium-nitride (GaN), known for its ability to detect ultraviolet illumination, is a top choice for making these detectors. In this letter, we introduce a GaN photodetector designed with a hexagonal nano-spikes-like structure that enhances performance and allows it to operate without an external power source. We delve into how surface potential is pivotal in its self-biasing capability. This device shows remarkable performance, including a high responsitivity of 2100 mAW−1 and the ability to detect very weak-signals (4 femto-watts) under self-bias condition. Our findings pave the way to fabricate a GaN-based self-bias optoelectronic device.

High-performance Ga2O3 solar-blind UV photodetectors via film growth regulation and surface state engineering

Gallium oxide (Ga2O3) with a wide bandgap is emerging as one of the most promising candidates for solar-blind photodetectors (SBPDs). However, the practical application of Ga2O3-based SBPDs is impeded by substantial defects-related leakage currents, sluggish response speed, and high-cost, making their practical applications face great challenges. Here, we proposed strategic films growth regulation and surface state engineering to grow high-quality yet economical β-Ga2O3 films, thereby achieving high-performance SBPDs. High-resolution transmission electron microscopy revealed the presence of high-quality films with an extremely regular arrangement of β-Ga2O3 (2‾01) planes. The full width at half maximum and root mean square roughness values are 0.07° and 0.716 nm, respectively. The β-Ga2O3 films demonstrated a significant reduction in VO concentrations after O2/N2 plasma treatment. This process can effectively minimize thermal damage to the sample surface while retaining highly reactive free radicals. The photocurrents of devices can be further enhanced, leading to a larger PDCRs of 8.6 × 107, through N2 plasma treatment. Moreover, the films effectually suppress the persistent photoconductivity effect with τr and τd values of 5.31/0.97 s and 0.49/0.87 s before and after N2 plasma treatment, respectively. We have demonstrated the influence mechanism of O2/N2 plasma treatment on photoelectronic performance. This study provides a practical approach to growing high-quality β-Ga2O3 films and preparing high-performance but low-cost Ga2O3-based SBPDs.

Fabrication of Al doped α-GaOOH nanorod arrays on FTO for self-powered photoelectrochemical solar-blind UV photodetectors

Al doped α-GaOOH nanorod arrays were grown on FTO via hydrothermal processes by using gallium nitrate and aluminum nitrate mixed aqueous solutions with fixed 1:1 mole ratio as precursors. With increasing the gallium nitrate precursor concentrations, the Ga/Al atom ratios in nanorod arrays increase from 0.36 to 2.08, and the length becomes much longer from 650 nm to 1.04 μm. According to the binding energy difference between Ga 2p3/2 core level and its background in x-ray photoelectron spectroscopy, the bandgap is estimated to be around 5.3 ± 0.2 eV. Al doped α-GaOOH nanorod array/FTO photoelectrochemical photodetectors show enhanced self-powered solar-blind UV photodetection properties, with the decrease of Ga precursor concentrations. The maximum responsivity at 255 nm is 0.09 mA W−1, and the fastest response time can reach 0.05 s. The improved photoresponse speed is ascribed from much shorter transportation route, accelerated carrier recombination by recombination centers, and smaller charge transfer resistance at the α-GaOOH/electrolyte interface with decreasing the gallium nitrate precursor concentrations. The stability and responsivity should be further improved. Nevertheless, this work firstly demonstrates the realization of self-powered solar-blind UV photodetection for α-GaOOH nanorod arrays on FTO via Al doping.

High-performance solar-blind photodetectors based on Ta-doped ZnSnO3 single crystal thin films

High-quality Ta-doped ZnSnO3 single crystal thin films were grown on LiTaO3 substrates by pulsed laser deposition (PLD) method, and the effects of Ta doping on the lattice structure, surface morphology, electronic structure and photodetector performance of ZnSnO3 thin films are studied in detail. When the Ta doping content is 1 %, the [0001]-oriented ZnSnO3 thin film present the highest quality, which the optical band gap (3.75 eV), the smoothest surface roughness (0.83 nm), and the biggest carrier concentration (4.03 × 1019 cm−3). For the solar-blind photodetectors (PDs), based on these excellent characteristics, the 1 % Ta-doped ZnSnO3 PD exhibits large light-to-dark current ratio (>103), responsivity (21.37 A/W), detectivity ((3.63±0.71) ×1011 Jones) and external quantum efficiency (∼1.04× 104 %) under 254 nm UV light at an applied bias of 5 V. This study suggests that Ta doping can effectively improve the optoelectronic performance of ZnSnO3 PDs, laying the foundation for their application.

Enhancement of solar blind full band absorption in photodetector with Ga2O3 nanopore and Al nanograting

In this paper, we presented a novel double-layer light-trapping structure consisting of nanopores and nanograting positioned on both the surface and bottom of a gallium oxide-based solar-blind photodetector. Utilizing the finite element method (FEM), we thoroughly investigated the light absorption enhancement capabilities of this innovative design. The simulation results show that the double-layer nanostructure effectively combines the light absorption advantages of nanopores and nanogratings. Compared with thin film devices and devices with only nanopore or nanograting structures, double-layer nanostructured devices have a higher light absorption, achieving high light absorption in the solar blind area.

Heteroepitaxial growth of Ga2O3 thin films on nickel-nanodot-induced buffer layers for solar-blind ultraviolet photodetector applications

Heteroepitaxial growth of gallium oxide (Ga2O3) thin films has been conducted on nickel (Ni)-nanodot-induced buffer layers using a mist chemical vapor deposition. The separation degree and droplet size of the Ni nanodots on sapphire substrates were controlled through a thermal annealing process, thereby being used as templates for the Ga2O3 thin-film growth. The growth of the inverted cone-shaped ε-Ga2O3 polymorph was observed on the nanodots while the α-Ga2O3 polymorph was grown on the sapphire substrate without nanodots, ultimately a thin film with a mixture of ε and α polymorphs can be achieved. By comparing photoresponses of metal–semiconductor–metal photodetectors fabricated on the thin film with the mixed polymorphs and on a single-crystalline α-Ga2O3 film, a promising template for using solar-blind photo-detecting applications has been verified.

Amorphous Ga2O3-based solar-blind photodetectors on crystalline and amorphous substrates: A comparative study

Amorphous Ga2O3 thin films were deposited on SiO2 and sapphire substrates by pulsed magnetron sputtering (PSD) at room temperature, respectively. Corresponding amorphous Ga2O3 thin film photodetectors were prepared. The oxygen vacancies and defects of the interface between films and substrates were found to determine the discrepancy by comparing the performance between these two photodetectors. Amorphous Ga2O3 photodetectors on SiO2 had highly performances with a responsivity of 417 A/W, detectivity of 7.84 × 1012 Jones, and external quantum efficiency of 2.01 × 105 %.

Liquid-Metal-Based Spin-Coating Exfoliation for Atomically Thin Metal Oxide Synthesis.

Two-dimensional (2D) semiconductors possess exceptional electronic, optical, and magnetic properties, making them highly desirable for widespread applications. However, conventional mechanical exfoliation and epitaxial growth methods are insufficient in meeting the demand for atomically thin films covering large areas while maintaining high quality. Herein, leveraging liquid metal oxidation reaction, we propose a motorized spin-coating exfoliation strategy to efficiently produce large-area 2D metal oxide (2DMO) semiconductors with high crystallinity, atomically thin thickness, and flat surfaces on diverse substrates. Moreover, we realized a 2D gallium oxide-based deep ultraviolet solar-blind photodetector featuring a metal-semiconductor-metal structure, showcasing high responsivity (8.24 A W-1) at 254 nm and excellent sensitivity (4.3 × 1012 cm Hz1/2 W-1). This novel liquid-metal-based spin-coating exfoliation strategy offers great potential for synthesizing atomically thin 2D semiconductors, opening new avenues for future functional electronic and optical applications.