Deep Ultraviolet Photodetectors Research Articles

Recent Progress of Deep Ultraviolet Photodetectors using Amorphous Gallium Oxide Thin Films

Deep ultraviolet (UV) photodetectors have wide applications both in civil and military fields. Many materials have been explored to realize deep UV photodetection. Amorphous gallium oxide (a‐GaOx), as a member of transparent amorphous oxide semiconductors (TAOSs), has attracted a great deal of attention due to its ultrawide bandgap and scalable synthesis at room temperature. Plenty of researches have been focused on this topic in recent years. Herein, the latest progresses in the preparation methods of a‐GaOx using radio‐frequency sputtering, pulsed laser deposition, atomic layer deposition, and other deposition techniques are summarized. Dependence of the stoichiometry, crystallinity, optical, electrical, and morphological properties on different preparation parameters and doping/alloying elements is tentatively discussed, as well as those deep UV photodetectors based on a‐GaOx and related thin films. Finally, a short summary with further possible investigations is provided for a better understanding and development of a‐GaOx materials and photodetectors.

ZnGa2O4 deep-ultraviolet photodetector based on Si substrate

Deep-ultraviolet photodetectors with fast response speed are urgently required in flame detection and atmospheric monitoring. A method for reducing oxygen vacancies in ZnGa2O4 films by high-temperature and oxygen thermodynamic conditions is proposed, to increase the response speed of ZnGa2O4/Si heterojunction deep-ultraviolet photodetectors. Here, a ZnGa2O4/Si heterojunction deep-ultraviolet photodetector with excellent performance is fabricated, exhibiting a decay time of ~67 ms, a dark current of 0.027 nA and a photo-to-dark current ratio of ~490. These results indicate that the high-temperature and oxygen-rich annealing method proposed here can provide a reference for the fabrication of ZnGa2O4 deep-ultraviolet photodetectors with excellent performance.

Photovoltaic and flexible deep ultraviolet wavelength detector based on novel \u03b2-Ga2O3/muscovite heteroepitaxy

Flexible and self-powered deep ultraviolet (UV) photodetectors are pivotal for next-generation electronic skins to enrich human life quality. The fabrication of epitaxial β-Ga2O3 thin films is challenging on flexible substrates due to high-temperature growth requirements. Herein, β-Ga2O3 (stackrel{-}{2} 0 1) films are hetero-epitaxially grown on ultra-thin and environment-friendly muscovite mica which is the first time β-Ga2O3 epitaxy growth on any flexible substrate. Integration of Gallium oxide with muscovite enables high-temperature processing as well as excellent flexibility compared to polymer substrates. Additionally, the metal–semiconductor-metal (MSM) photodetector on β-Ga2O3 layer shows an ultra-low dark current of 800 fA at zero bias. The photovoltaic peak responsivity of 11.6 µA/W is obtained corresponding to very weak illumination of 75 μW/cm2 of 265 nm wavelength. Thermally stimulated current (TSC) measurements are employed to investigate the optically active trap states. Among these traps, trap with an activation energy of 166 meV dominates the persistence photocurrent in the devices. Finally, photovoltaic detectors have shown excellent photocurrent stability under bending induced stress up to 0.32%. Hence, this novel heteroepitaxy opens the new way for flexible deep UV photodetectors.

Patterned growth of β-Ga2O3 thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

Solar-blind deep-ultraviolet (DUV) photodetectors based on Ga2O3 have attracted great attention due to their potential applications for many military and civil purposes. However, the development of device integration for optoelectronic system applications remains a huge challenge. Herein, we report a facile method for patterned-growth of high-quality β-Ga2O3 thin films, which are assembled into a photodetectors array comprising 8 × 8 device units. A representative detector exhibits outstanding photoresponse performance, in terms of an ultra-low dark current of ∼0.62 pA, a large Ilight/Idark ratio exceeding 104, a high responsivity of ∼0.72 A W−1 and a decent specific detectivity of ∼4.18 × 1011 Jones, upon 265 nm DUV illumination. What is more, the DUV/visible (250/400 nm) rejection ratio is as high as 103 with a sharp response cut-off wavelength at ∼280 nm. Further optoelectronic analysis reveals that the photodetectors array has good uniformity and repeatability, endowing it the capability to serve as a reliable DUV light image sensor with a decent spatial resolution. These results suggest that the proposed technique offers an effective avenue for patterned growth of β-Ga2O3 thin films for multifunctional DUV optoelectronic applications.

A 2DEG back-gated graphene/AlGaN deep-ultraviolet photodetector with ultrahigh responsivity* *Project supported by the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications (Grant No. 202002046) and the National Natural Science Foundation of China (Grant No. 61804012).

A graphene/AlGaN deep-ultraviolet (UV) photodetector is presented with ultrahigh responsivity of 3.4 × 105 A/W at 261 nm incident wavelength and 149 pW light power. A gain mechanism based on electron trapping at the potential well is proposed to be responsible for the high responsivity. To optimize the trade-off between responsivity and response speed, a back-gate electrode is designed at the AlGaN/GaN two-dimensional electron gas (2DEG) area which eliminates the persistent photocurrent effect and shortens the recovery time from several hours to milliseconds. The 2DEG gate is proposed as an alternative way to apply the back gate electrode on AlGaN based devices on insulating substrates. This work sheds light on a possible way for weak deep-UV light detection.

Enhanced performance of solar-blind photodetector of hexagonal boron nitride with bottom-contact electrodes

A deep ultraviolet photodetector has wide applications in both military and civil fields, such as the missile early warning system, transparent wireless communication, environmental monitoring, and so on. Because of its wide bandgap, hexagonal boron nitride (h-BN) has been envisioned to be a promising material for deep ultraviolet photodetectors. In this work, we have synthesized high-quality h-BN crystals using the flux growth method at atmospheric pressure. Based on the thin-layered h-BN prepared by mechanical exfoliation, two types of solar-blind photodetectors, with either top-contact or bottom-contact electrodes, were fabricated. It is found that the device with bottom-contact electrodes exhibits excellent performance in the specific detectivity exceeding 3.68 × 108 Jones (cm Hz1/2 W−1) at 215 nm. Moreover, the photodetectors have a cutoff wavelength at about 270 nm, which demonstrates that the device can be an ideal candidate for a solar-blind photodetector.

Bandgap-Tuned 2D Boron Nitride/Tungsten Nitride Nanocomposites for Development of High-Performance Deep Ultraviolet Selective Photodetectors.

This study presents a fast and effective method to synthesize 2D boron nitride/tungsten nitride (BN–WN) nanocomposites for tunable bandgap structures and devices. A few minutes of synthesis yielded a large quantity of high-quality 2D nanocomposites, with which a simple, low-cost deep UV photo-detector (DUV-PD) was fabricated and tested. The new device was demonstrated to have very good performance. High responsivity up to 1.17 A/W, fast response-time of lower than two milliseconds and highly stable repeatability were obtained. Furthermore, the influences of operating temperature and applied bias voltage on the properties of DUV-PD as well as its band structure shift were investigated.

Realization of Deep UV Plasmonic Enhancement to Photo Response through Al Mesh.

High-performance UV detectors are of great significance for various applications. Plasmonic structures enable great improvement of the performance of detectors. However, to push the plasmonic enhancement to photo response into the deep-UV region presents some challenges. In this work, we found that the optical properties of the supporting layer play important roles in achieving the optimal plasmonic enhancement. Therefore, we fully considered the dependence of the optical constants of the MgZnO supporting layer, which is a promising material to realize deep-UV photodetectors, on microstructure and crystalline quality, which are related to the fabrication method. Based on the optical constants, we designed an Al mesh plasmonic structure and fabricated it with a polystyrene monolayer as a mask. Finally, we demonstrated a three-times enhancement to photo response with UV radiation at 254 nm.

Nanolayered Graphene/Hexagonal Boron Nitride/n-AlGaN Heterostructures as Solar-Blind Deep-Ultraviolet Photodetectors

The spectral specificity of deep-ultraviolet (UV) photodetectors makes them useful in many fields, spanning from disinfection of various surfaces and water purification to optical communication. As...

High-Performance Deep Ultraviolet Photodetector Based on a One-Dimensional Lead-Free Halide Perovskite CsCu2I3 Film with High Stability.

Lead halide perovskites have received much attention in the field of optoelectronic devices. However, the environment-unfriendly nature and intrinsic instability of these perovskites hamper their commercial applications. In this work, one novel one-dimensional lead-free halide perovskite with high stability, CsCu2I3, was prepared via an antisolvent-assisted crystallization method. The prepared CsCu2I3 bears a high exciton binding energy of ∼105 meV and a high photoluminescence quantum yield of 12.3%. We fabricated a deep ultraviolet photodetector based on a CsCu2I3 film that is nearly blind to 405 nm visible light but is sensitive to 265 and 365 nm illumination. The device exhibits excellent reproducibility and a high Ilight/Idark ratio of 22 under 265 nm illumination. Furthermore, the responsivity, specific detectivity, and external quantum efficiency are as high as 22.1 mA/W, 1.2 × 1011 Jones, and 10.3% under a light density of 0.305 mW/cm2, respectively. These findings demonstrate that CsCu2I3 perovskites should have great potential for future optoelectronics.

Influence of titanium adhesion layer on performance of β-Ga2O3 solar-blind photodetector

The influence of a titanium (Ti) adhesion layer on the ductility of thin Au film well bonded with β-Ga2O3 film on a flexible substrate were investigated with the quality of β-Ga2O3 deep-ultraviolet photodetector. The photodetector fabricated with Ti adhesion layer exhibits excellent photoelectric performance and stability. The photocurrent obtained by the Ti/Au bilayer-device (3.1 × 10−8 A) is significantly greater than that of an Au electrode-device (1.7 × 10−8 A) at 10 V under a flat state. After 250 bending cycles, the photoresponsivity of the Au electrode-device declined approximately 20 times, while little photoresponsivity degradation was observed in the Ti/Au bilayer-device. Additionally, more suppression of the deformation and cracks was observed in the Au film with Ti adhesion layer than the Au grown directly on the β-Ga2O3 films. These results reveal the importance of the adhesion layer in promoting the photodetector.

Contact barriers modulation of graphene/β-Ga2O3 interface for high-performance Ga2O3 devices

The ultra-wide-gap β-Ga2O3 has been regarded as a promising material for next-generation power electronic and deep-ultraviolet (UV) photodetectors. Exploring a suitable electrode is vital for realizing high performance β-Ga2O3 based nanodevices. Herein, the structural and contact properties of graphene/Ga2O3 interfaces are tuned and investigated by using the first-principles calculations. Results show that the small n-type Schottky barrier of about 0.07 eV for the graphene/Ga2O3 interface with weak interlayer interaction is irrespective of the interface stacking arrangement. Moreover, the intrinsic electronic property of Ga2O3 is well preserved in the interface. More interestingly, the n-type Schottky barrier to Ohmic contact transition can be obtained by shorting the interlayer distance, or increasing the graphene layers or applying a negative external electric field for the interface. Moreover, applying a large positive external electric field can realize the p-type Schottky barrier to Ohmic contact transition for graphene/Ga2O3 interface. These results are uncovered by analyzing the interfacial dipole and potential step of graphene/Ga2O3 interface, and expected to enhance the application potential of graphene electrode in the β-Ga2O3 based electronic and optoelectronic devices.

AlGaN-based Schottky barrier deep ultraviolet photodetector grown on Si substrate.

This letter reports the influence of material quality and device processing on the performance of AlGaN-based Schottky barrier deep ultraviolet photodetectors grown on Si substrates. The thermal annealing can significantly improve Schottky barrier height and wet chemical etching can effectively remove etching damage. Meanwhile, the decrease of threading dislocation density and the pit size, especially the later, can substantially suppress reverse leakage. As a result, the reverse leakage current density of the as-fabricated deep UV photodetector was reduced down to 3×10-8 A/cm2. Furthermore, the responsivity of the deep UV photodetectors was greatly improved by reducing the point defect concentration.

Deep Ultraviolet Photodetectors Based on Carbon-Doped Two-Dimensional Hexagonal Boron Nitride.

Recently, the deep ultraviolet (DUV) photodetectors fabricated from two-dimensional (2D) hexagonal boron nitride (h-BN) layers have emerged as a hot research topic. However, the existing studies show that the h-BN-based photodetectors have relatively poor performance. In this work, C doping is utilized to modulate the properties of h-BN and improve the performance of the h-BN-based photodetectors. We synthesized the h-BN atomic layers with various C concentrations varying from 0 to 10.2 atom % by ion beam sputtering deposition through controlling the sputtering atmosphere. The h-BN phase remains stable when a small amount of C is incorporated into h-BN, whereas the introduction of a large amount of C impurities leads to the rapidly deteriorated crystallinity of h-BN. Furthermore, the DUV photodetectors based on C-doped h-BN layers were fabricated, and the h-BN-based photodetector with 7.5 atom % C exhibits the best performance with a responsivity of 9.2 mA·W-1, which is significantly higher than that of the intrinsic h-BN device. This work demonstrates that the C doping is a feasible and effective method for improving the performance of h-BN photodetectors.

P-type β-Ga2O3 metal-semiconductor-metal solar-blind photodetectors with extremely high responsivity and gain-bandwidth product

P-type β-Ga2O3 films deep-ultraviolet (DUV) solar-blind metal-semiconductor-metal (MSM) photodetectors (PDs) are fabricated with extremely high photoresponsivity (9.5 × 103 A/W), external quantum efficiency (4.7 × 106%), detectivity (1.5 × 1015 Jones), and gain-bandwidth product (106) at 5 V bias, very low noise equivalent power (4.9 × 10−16 W/Hz1/2) and high specific detectivity (1.9 × 1013 Jones) at 1 kHz and 3 V bias. The excellent performances of the p-type β-Ga2O3 DUV MSM PDs are attributed to the charge carrier multiplication via collective excitation of aggregated excitons and/or electron-hole liquid within the fabricated high-quality p-type β-Ga2O3 films, which possess the room-temperature Hall resistivity of 52.6 Ωcm, the hole mobility of 41.4 cm2/V⋅s, and the hole concentration of 2.86 × 1015 cm−3. The unprecedentedly high photoresponsivity and detectivity and the carrier multiplication mechanism in high-quality p-type β-Ga2O3 films pave a novel way to fabricate super sensitive DUV PDs based on p-type wide-bandgap oxide semiconductors.

Ultra-high responsivity (>12.34 kA W−1) of Ga–In bimetallic oxide nanowires based deep-UV photodetector

This work demonstrates the application of bimetallic oxide nanowires (NWs) for deep UV-photodetectors. The Ga–In based NWs have been fabricated using a low cost and scalable electrospinning method. The fabrication process includes the synthesis of NWs on cleaned quartz substrates using electrospinning, followed by Al (100 nm)/Au (20 nm)-electrode deposition on top of the fine sheet of NWs. Due to the very large surface to volume ratio, high porosity, photon trapping and simultaneous front and back illumination, the fabricated bimetallic photodetector demostrates a record ultra-high responsivity and the photo-dark current ratio of ~12 348 AW−1 and ~298 846 at 1 V bias respectively. The device has further revealed high detectivity ~3.27 × 1015 mHz0.5 W−1 and external quantum efficiency ~7.73 × 106%.

Solar-blind deep-ultraviolet photodetectors based on solution-synthesized quasi-2D Te nanosheets

Abstract Solar-blind deep ultraviolet (DUV) photodetectors with high responsivity (R) and fast response speed are crucial for practical applications in astrophysical analysis, environmental pollution monitoring, and communication. Recently, 2D tellurium has emerged as a potential optoelectronic material because of its excellent photoelectric properties. In this study, solar-blind DUV photodetectors are demonstrated based on solution-synthesized and air-stable quasi-2D Te nanosheets (Te NSs). An R of 6.5 × 104 A/W at 261 nm and an external quantum efficiency (EQE) of higher than 2.26 × 106% were obtained, which are highest among most other 2D material-based solar-blind DUV photodetectors. Moreover, the photoelectric performance of the quasi-2D Te-based photodetector exhibited good stability even after ambient exposure for 90 days without any encapsulation. These results indicate that quasi-2D Te NSs provide a viable approach for developing solar-blind DUV photodetectors with ultrahigh R and EQE.

Titania:Graphdiyne nanocomposites for high-performance deep ultraviolet photodetectors based on mixed-phase MgZnO

Approachable graphdiyne (GDY), characterized by discrepancy hybridized carbon atoms of inhomogeneous π-bonding and carbon 2pz overlapping of orbitals, reveals versatility applications. Previously, interfaces high density between different structure materials induce the high response of photodetector, but the ratio of photocurrent to dark current is restricted for either limited materials properties or lattice mismatch when junctions formed. In this work, titania (TiO2) nanocrystals with a rational phase of anatase are encapsulated on GDY particles, further, the TiO2:GDY nanocomposites are synthesized. High specific surface area GDY, as a proper sustaining material optimizes the characters of TiO2 nanocrystals. Then TiO2:GDY nanocomposites cooperate with Mg0.3Zn0.7O (MZO) are mean to fabricate lateral bilayer ultraviolet photodetector. Because of the formed heterojunction between TiO2:GDY nanocomposites and MZO, the ultraviolet photodetector is highly sensitive to deep ultraviolet light, when optical band gap of MZO is as high as 3.8 eV. The responsivity of TiO2:GDY/MZO bilayer photodetector is also increased by more than one order of magnitude to 76 mA W−1 compares to the MZO device without TiO2:GDY nanocomposites while the photocurrent rejection is about three orders of magnitude from 254 nm to 365 nm. Meanwhile, signal-to-noise ratio is calculated as high as 1.5 × 105 in this work.

First-principle investigation of monoclinic (AlxInyGa1−x−y)2O3 quaternary alloys

First-principle density functional theory calculations were performed to explore electronic and structural properties of β-(AlxInyGa1−x−y)2O3 quaternary alloys with both Al-content (x) and In-content (y) ranging from 0% to 18.75%. The β-(AlxInyGa1−x−y)2O3 quaternary alloys exhibit indirect band gap property with the bandgap energy varying from 4.432 to 5.171 eV. Electron effective masses are also presented for β-(AlxInyGa1−x−y)2O3 quaternary alloys, showing a general reduction with In-content increases but a general increment with Al-content increases in the material. Further analysis indicates the possibility of achieving lattice-matched or near-lattice-matched β-(AlxInyGa1−x−y)2O3/β-Ga2O3 structures system, which is critical for high performance field effect transistor and deep ultraviolet photodetector applications. Our work shows that the β-(AlInGa)2O3 alloys with proper tuning of Al- and In-content have strong potential to be used as part of the epitaxial layers for β-Ga2O3-based material system.

Ultrathin Polymer Nanofibrils for Solar-Blind Deep Ultraviolet Light Photodetectors Application.

Solar-blind deep ultraviolet photodetectors (DUVPDs) based on conventional inorganic ultrawide bandgap semiconductors (UWBS) have shown promising application in various civil and military fields and yet they can hardly be used in wearable optoelectronic devices and systems for lack of mechanical flexibility. In this study, we report a non-UWBS solar-blind DUVPD by designing ultrathin polymer nanofibrils with a virtual ultrawide bandgap, which was obtained by grafting P3HT with PHA via a polymerization process. Optoelectronic analysis reveals that the P3HT-b-PHA nanofibrils are sensitive to DUV light with a wavelength of 254 nm but are virtually blind to both 365 nm and other visible light illuminations. The responsivity is 120 A/W with an external quantum efficiency of up to 49700%, implying a large photoconductive gain in the photoresponse process. The observed solar-blind DUV photoresponse is associated with the resonant mode due to the leakage mode of the ultrathin polymer nanofibrils. Moreover, a flexible image sensor composed of 10 × 10 pixels can also be fabricated to illustrate their capability for image sensing application. These results signify that the present ultrathin P3HT-b-PHA nanofibrils are promising building blocks for assembly of low-cost, flexible, and high-performance solar-blind DUVPDs.