Deep Ultraviolet Photodetectors Research Articles

2D–3D heterostructure of PtS2−x /Ga2O3 and their band alignment studies for high performance and broadband photodetector

For deep ultraviolet (UV-C) photodetectors, gallium oxide (Ga2O3) is a suitable candidate owing to its intrinsic ultra-wide band gap and high stability. However, its detection is limited within the UV-C region, which restricts it to cover a broad range, especially in visible and near-infrared (NIR) region. Therefore, constructing a heterostructure of Ga2O3 with an appropriate material having a narrow band gap is a worthwhile approach to compensate for it. In this category, PtS2 group-10 transitional metal dichalcogenide stands at the top owing to its narrow band gap (0.25–1.65 eV), high mobility, and stability for heterostructure synthesis. Moreover, heterostructure with Ga2O3 sensing in UV and PtS2 broad response in visible and IR range can broaden the spectrum from UV to NIR and to build broadband photodetector. In this work, we fabricated a 2D–3D PtS2−x /Ga2O3 heterostructure based broadband photodetector with detection from UV-C to NIR region. In addition, the PtS2−x /Ga2O3 device shows a high responsivity of 38.7 AW−1 and detectivity of 4.8 × 1013 Jones under 1100 nm light illumination at 5 V bias. A fast response of 90 ms/86 ms illustrates the device’s fast speed. An interface study between the PtS2−x and Ga2O3 was conducted using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy (UPS) which confirmed type-I band alignment. Finally, based on their band alignment study, a carrier transport mechanism was proposed at the interface. This work offers a new opportunity to fabricate large-area high-performance 2D–3D heterostructures based photodetectors for future optoelectronics devices.

High-performance and low-power consumption deep UV photodetectors based on MOCVD-grown ZnGa2O4epilayers with high temperature functionality

This work reports on the fabrication of excellent quality deep ultraviolet photodetectors (DUV PDs) based on metalorganic chemical vapor deposition (MOCVD) grown spinel ZnGa2O4 thin films on c-plane sapphire. Herein, The DUV PDs by exhibiting an ultra-low dark current of 6.69 fA and a high photo-to-dark-current ratio (PDCR) of >108 at a low-power operation of 0.2 V. While PDCR reached more than 109 on applied bias of 10 V having extremely low dark current of 37 fA. The detector revealed an ultra-high responsivity of 185 and 3.53 A/W under the exposure of 107 μW/cm2 of 245 nm wavelength at room temperature (RT) and applied bias of 10 and 0.2 V, respectively, and exhibited the record-high detectivity of the order of 1017 Jones. The temperature-dependent operation remained stable across a wide temperature range, from 27 °C to 125 °C, maintaining ultra-low dark current. The nearly constant growth and decay time of DUV PDs throughout the temperature range emphasizes the robustness and reliability of PD. The ideality factor in both DUV and dark conditions nearing unity proves the dominance of the thermionic emission mechanism. Also shows the stable and slight improved performance after a year. Therefore, these findings suggest that ZnGa2O4 is a strong contender for deep UV detection that shows robustness even at high temperatures.

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.

A self-powered and flexible deep ultraviolet photodetector based on NiO/Ga2O3 heterojunction and employing stable MXene electrodes

Wearable photodetectors (PDs) have gained significant attention for their importance in smart monitoring applications. The future of wearable electronics emphasizes the development of self-powered devices, necessitating precise material selection and fabrication techniques to achieve optimal electrical and mechanical performance. Traditionally, p-n photodetector junctions have been fabricated using non-oxide materials such as GaN and SiC, but these materials are prone to conductivity degradation due to oxidation of the p-type component. In this investigation, we have successfully engineered a NiO/Ga2O3 heterojunction deep ultraviolet photodetector on both rigid and flexible substrates. The flexible version incorporates Ti3C2TX MXene electrodes, which offer exceptional mechanical stability even in harsh mechanical circumstances. Our photodetector showcases a responsivity of 47 μA/W, a photoresponse time of 0.24 s, a specific detectivity (D*) of 3.84 ×109 jones, and an Ilight/Idark ratio of 121. It also demonstrates excellent repeatability under 254 nm light exposure. The NiO/Ga2O3 heterojunction photodetector exhibits outstanding optoelectronic performance even under harsh mechanical conditions, specifically withstanding 40% stretchability and various bending angles while maintaining self-powered capabilities. This makes it ideal for wearable devices, meeting requirements for both durability and functionality.

Substrate temperature dependent crystal structure and deep-ultraviolet photodetection of ZnGa2O4 thin films * *Project supported by This work was supported by the National Natural Science Foundation of China (No. 12074044), the Fund of State Key Laboratory of Information Photonics and Optical Communications (IPOC2021ZT05), and the Fundamental Research Funds for the Central Universities (BUPT, 2023ZCJH1).

Zinc gallate (ZnGa2O4) is a promising material for deep-ultraviolet (DUV) photodetectors, owing to its wide bandgap and high transparency. However, the effect of substrate temperature on the structural and optical properties of ZnGa2O4 thin films prepared by magnetron sputtering is not well understood. Here, we report a systematic study of the influence of substrate temperature on the crystal quality, stoichiometry, bandgap, and photodetection performance of ZnGa2O4 thin films deposited on sapphire substrates. We find that the films undergo a phase transition from amorphous to polycrystalline at 300 °C, and then to single crystalline at 500 °C, accompanied by an increase in the bandgap from 4.6 to 4.9 eV. We also fabricate metal-semiconductor–metal photodetectors based on the ZnGa2O4 thin films with Ti/Au electrodes, which exhibit excellent Ohmic contact and high light-to-dark current ratio. The photodetectors show remarkable and stable DUV response, with the highest performance achieved at a substrate temperature of 650 °C. Our results demonstrate the crucial role of substrate temperature in tailoring the crystal structure and DUV photodetection of ZnGa2O4 thin films, and provide a facile route for optimizing their performance.

Preparation of ZnGa2O4-based deep ultraviolet photodetector with high photodetectivity by magnetron sputtering

Ultra-wide bandgap semiconductors are frequently utilized materials in the fabrication of deep ultraviolet photodetectors (DUVPDs). However, it is imperative to enhance both the photoresponsivity and response speed of these detectors. Herein, we deposited high-quality (111)-oriented ZnGa2O4 films with a bandgap of approximately 4.75 eV onto c-plane sapphire (0001) substrates using magnetron sputtering. Our findings illuminate the pivotal role of pressure in shaping their structural properties, chemical compositions, and photoelectric characteristics. Importantly, DUVPDs based on ZnGa2O4 films exhibited a photo/dark current ratio of 1.46 × 104. Furthermore, we observed the highest responsivity to be 72.2 A/W, complemented by a photodetectivity of 4.21 × 1014 Jones, an external quantum efficiency of 4.04 × 104 %, and rise and decay times of 2.32 s and 0.055 s, respectively. This study underscores the commendable photoresponsivity and rapid response time of the ZnGa2O4 photodetector, positioning it as a compelling candidate for the advancement of deep ultraviolet devices.

Deep-ultraviolet n-ZnGa2O4/p-GaN heterojunction photodetector fabricated by pulsed laser deposition.

Zinc gallium oxide (ZnGa2O4) has attracted considerable interest in deep-ultraviolet photodetectors, due to the ultrawide bandgap, high transmittance in the ultraviolet (UV) region, and excellent environmental stability. In this study, ZnGa2O4 thin films were deposited on p-GaN epi-layers using pulsed laser deposition, resulting in improved crystalline quality. The ZnGa2O4 film exhibited a bandgap of 4.93 eV, calculated through absorption spectra. A heterojunction photodetector (PD) was constructed, demonstrating a rectification effect, an on/off ratio of 12,697 at -5.87 V, a peak responsivity of 14.5 mA/W, and a peak detectivity of 1.14 × 1012 Jones (262 nm, -6 V). The PD exhibited a fast response time (39 ms) and recovery time (30 ms) under 262 nm illumination. The band diagram based on the Anderson model elucidates the photoresponse and carrier transport mechanism. This work paves the way for advancing next-generation optoelectronics.

MXene/AlGaN van der Waals heterojunction self-powered photodetectors for deep ultraviolet communication

Self-powered deep ultraviolet (DUV) photodetectors (PDs) have attracted considerable attention in environmental, industrial, and military fields because of their power-independent and environmentally sensitive photodetection. However, DUV PDs based on traditional thin film structures are limited by the low intrinsic mobility of aluminum-gallium nitride (AlGaN) and the large barrier width of the heterogeneous structure, which makes it difficult to achieve efficient spontaneous separation, resulting in lower responsiveness and a slow response speed. Herein, a 2D/3D DUV PD based on the MXene, niobium carbide (Nb2CTx)/AlGaN van der Waals heterojunctions (vdWHs) has been proposed. The as-prepared DUV PDs revealed self-powered properties with a high responsivity of 101.85 mA W−1, as well as a fast response (rise/decay time of 21/22 ms) under 254 nm DUV illumination, thanks to the excellent electrical conductivity and tunable work function of the MXene. It also showed a large linear dynamic range of 70 dB under −2 V bias because of the strong DUV absorption of MXene/AlGaN vdWH, and the enhanced carrier mobility under high illumination density. This study presents an easy processing route to fabricate high-performance self-powered DUV PDs based on MXene/AlGaN vdWHs for DUV communication.

Self-powered deep ultraviolet photodetector based on p-CuI/n-ZnGa2O4 heterojunction with high sensitivity and fast speed.

Self-powered deep ultraviolet photodetectors (DUV PDs) are essential in environmental monitoring, flame detection, missile guidance, aerospace, and other fields. A heterojunction photodetector based on p-CuI/n-ZnGa2O4 has been fabricated by pulsed laser deposition combined with vacuum thermal evaporation. Under 260 nm DUV light irradiation, the photodetector exhibits apparent self-powered performance with a maximum responsivity and specific detectivity of 2.75 mA/W and 1.10 × 1011 Jones at 0 V. The photodetector exhibits high repeatability and stability under 260 nm periodic illumination. The response and recovery time are 205 ms and 133 ms, respectively. This work provides an effective strategy for fabricating high-performance self-powered DUV photodetectors.

Deep and Near UV Photodetector Based Upon Zirconium Diboride and n-Doped Silicon Carbide

Deep and Near UV Photodetector Based Upon Zirconium Diboride and n-Doped Silicon Carbide

Gallium oxide nanocrystals for self-powered deep ultraviolet photodetectors

Zero-dimensional colloidal nanocrystals (NCs) of gamma-phased gallium oxide (γ-Ga2O3) were successfully synthesized using the sol-gel method, resulting in nanocrystals with high crystallinity. Heterojunction photodetectors were then constructed by employing spin-coating technology to deposit γ-Ga2O3 NCs film of varying thicknesses onto p-type GaN substrates. The resulting devices demonstrated self-power capability through a photovoltaic effect when exposed to ultraviolet light illumination. Notably, a device with a 300 nm thick active layer, annealed in 400 °C, exhibited a responsivity of 6.7 × 10–3 A W–1, a detectivity of 3.10 × 1011 Jones, and an external quantum efficiency of 3.2 % under 254 nm light illumination at 0.16 mW cm–2, all without the need for an external power supply. These findings suggest promising practical applications for such photodetectors in single-point imaging systems. This study presents a straightforward and viable approach for developing high-performance and self-powered ultraviolet photodetectors based on zero-dimensional γ-Ga2O3 NCs, thereby opening up possibilities for various photonic systems and applications that do not rely on an external power supply.

Thermodynamic, electronic, and optical properties of ultra-wide bandgap zirconium-doped tin dioxide from a DFT perspective.

The effects of zirconium doping on the thermodynamic, electronic, and optical properties of tin dioxide are investigated by using density functional theory calculations combined with the cluster expansion method. In the whole composition range, the formation enthalpies of all structures are positive, indicating that SnO2-ZrO2 is an immiscible system and the ZrSnO2 alloy has a tendency of phase separation at low temperature. The x-T phase diagram of ZrSnO2 ternary alloy shows that the critical temperature is 979 K, which means that when the growth temperature of ZrSnO2 crystal is higher than the critical temperature, it is possible to realize the full-component solid solution. The bandgaps of ZrxSn1-xO2 alloys (0 ≤ x ≤ 1) are direct and increase as the Zr composition increases. Zr doping can tune the bandgap of SnO2 from the ultraviolet-B region to the deep ultraviolet region, and has a strong optical response to deep ultraviolet light. The projected density of states and band offsets clearly reveal the reason for the increase of bandgap, which provides useful information to design relevant optoelectronic devices such as quantum wells and solar-blind deep ultraviolet photodetectors.

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

Unleashing the Power of Quantum Dots: Emerging Applications from Deep‐Ultraviolet Photodetectors for Brighter Futures

AbstractSince their discovery in 1981, quantum dots (QDs) have been the center of attention in optoelectronic fields owing to their excellent properties such as clearly discrete band structure, high luminous efficiency, and tunable energy bandgap via dot size control. Among them, the bandgap increase characteristic based on the quantum confinement effect opens a new horizon in the field of deep ultraviolet photodetectors (DUV PDs). Emerging applications such as risk monitoring, wireless optical communication, and chemical sensing with extremely low environmental interference raise the significance of DUV PDs. Nonetheless, the limited material selection for DUV absorption has been the main obstacle for further applications. Along this line, this review systematically revisits the recent advances in QD‐based DUV PDs, using bandgap‐widened QDs, with a focus on the synthetic method, device architecture, and interactions among constituent components. Various QDs categorized into carbon, oxide, sulfide, and nitride are reviewed with the specific characteristics of each substance. The future prospects of QD‐based DUV PDs in terms of practical applications and the current challenges are discussed.

(Invited) Leading-Edge Diamond FET, MEMS, and Photodetector Devices

Diamond is a candidate material for next-generation power electronics, micro-electro mechanical systems (MEMS), and solar-blind deep-ultraviolet (DUV) photodetector devices with excellent thermal stability and radiation hardness, which operate under extreme environment. In order to use an advantage of high-density hole channel of hydrogenated diamond (H-diamond) surface, we have developed the high-k stack gate dielectrics and AlN heterojuction gate for H-diamond FETs, such as HfO2/HfO2, LaAlO3/Al2O3 Ta2O5/Al2O3, and ZrO2/Al2O3, AlN/Al2O3 prepared by a combination of sputter-deposition (SD) and atomic layer deposition (ALD) techniques [1,2]. We also demonstrated the artificial diamond Fin-FETs with high-current level [3] and the nanolaminate insulator gate metal-oxide-gate FETs (MOSFETs) with k value as high as 100 [4], and the new transistor concept named by metal-insulator-metal-semiconductor field-effect transistor (MIMS-FET) to achieve normally-off operation by combining the advantages of MOSFET and metal-semiconductor FET [5]. In addition, we developed the routine ion-implantation process for preparing the diamond cantilever with a resonant frequency quality factor as high as one million [6,7]. We have also developed thermally stable Schottky barrier photodiode (SPD), metal-semiconductor-metal photodetector (MSMPD), and MSM-type SPD (IDF-SPD) with a large photoconductivity gain in DUV wavelength and a large discrimination ratio between DUV/visible light responsivity [8,9]. In this presentation, we will review the comprehensive our work on the diamond FET, MEMS, and photodetector devices. Acknowledgements: This work was in collaboration with J-W. Liu, M. Imura, M-Y. Liao, J. Alvarez in NIMS and A. Ouchiero and E. Obaldia in University of Taxes, Dallas, and partly supported by JSPS KAKENHI Grant Number 20H00313.

Synthesis and Characterization of High‐Quality Ta2O5 Nanoparticles for Highly Selective SAW‐Based DUV Sensor and Corona Detection Application

AbstractIn recent times, significant progress is made in the development of solar‐blind deep‐ultraviolet (DUV) photodetectors (200–280 nm) due to their potential applications for military and civil purposes. In this study, the development of a novel solar‐blind DUV photodetector based on tantalum pentoxide (Ta2O5) nanoparticles (NPs) utilizing Surface Acoustic Wave (SAW) sensor integrated with Interface electronics is reported for the first time. The 3‐D Ta2O5 NPs surface morphology, crystallinity, and defect state level is discussed using various analytical techniques, including scanning electron microscope (SEM), X‐ray diffraction (XRD), and spectrophotometer. The developed 3‐D Ta2O5 NPs based photodetector exhibits high sensitivity to 254 nm DUV irradiation (5 µW cm−2), demonstrating excellent photoresponse characteristics. The performance parameters including highest sensitivity, fast response/recovery time are measured as 1621.1 ppm (mW cm−2)−1, 3.7s/19.8s, respectively. Subsequent analysis demonstrates the stability and repeatability of the photodetector, enabling its potential to real time corona discharge detection. With its inherent advantages, the current DUV photodetector utilizing Ta2O5 NPs exhibits great potential for future applications in DUV optoelectronics.

Enhancing the performance of Self-Powered Deep-Ultraviolet photoelectrochemical photodetectors by constructing α-Ga2O3@a-Al2O3 Core-Shell nanorod arrays for Solar-Blind imaging

With the advancement of Ga2O3-based deep-ultraviolet (DUV) photodetectors (PDs), the integration of PDs into array image sensors has become a sought-after objective. However, while solar-blind imaging research primarily revolves around solid-state Ga2O3-based PDs, there remains a significant gap in the exploration of novel photoelectrochemical (PEC) PDs for solar-blind imaging applications. In this study, self-powered solar-blind PEC-PDs with enhanced performance are fabricated based on α-Ga2O3@a-Al2O3 core–shell nanorod arrays (NRAs). Under DUV irradiation and without external bias, the α-Ga2O3@a-Al2O3 devices demonstrate remarkable superiority over α-Ga2O3 devices. When the light intensity was at 0.50 mW cm−2, the photocurrent density notably rises from 4.60 to 11.24 μA cm−2, accompanied by a corresponding increase in responsivity from 9.60 to 22.70 mA W−1. The enhanced performance is attributed to the α-Ga2O3@a-Al2O3 heterostructure, which establishes a built-in electric field facilitating the separation and directed transport of photogenerated carriers at the interface. Moreover, for the first time, a 5 × 5 matrix of α-Ga2O3@a-Al2O3 core–shell NRAs-based PEC-type PDs is employed to demonstrate a proof-of-concept for self-powered solar-blind imaging, capable of effectively capturing the shapes of the letters “C” and “N”. This work underscores the immense potential of Ga2O3-based PEC-type PDs for future large-area solar-blind imaging applications.

Atmospheric-pressure CVD-grown h-BN for the detector with deep ultraviolet response

Hexagonal boron nitride (h-BN) has a wide range of applications, especially as a protective coating, dielectric layer/substrate, transparent film, or deep ultraviolet detectors. High-quality h-BN thick films are indispensable for practical deep-ultraviolet (DUV) photodetector applications. However, the controlled synthesis of h-BN films in terms of thicknesses and crystallinity often requires high growth temperatures, low pressures, and catalytic transition metal substrates, which will ultimately hinder their applicability. In this work, we conducted a detailed study of h-BN films with thickness ranging from 50 nm to 160 nm directly synthesized by chemical vapor deposition (CVD) on SiO2/Si substrate under atmospheric pressure. The synthesized h-BN is clean, uniform, and exhibits excellent optical and photoelectrical properties for ultraviolet light in the range of 210 nm-280 nm. This sensitive h-BN photodetector has a high repulsion rate (R220nm/R280nm > 102 and R220nm/ R290nm > 103), a large detection rate (2.8 × 1010 Jones). This work presented here demonstrates the great potential of this h-BN thick film for the development of DUV photodetectors.

Photocarrier transport reconstruction and dramatical performance enhancement in ultrawide-bandgap ε-Ga2O3 photodetectors via surface defect passivation

The semiconductor surface is a major platform dictating carrier transport and recombination, in particular for planar photoconductive devices such as metal-semiconductor-metal (MSM) photodetectors. Here we demonstrate the integration of an ultrathin Al2O3 capping layer to effectively passivate the surface defects of epitaxial ε-Ga2O3 films and substantially enhance the photodetector performance. Incorporating an Al2O3 layer is found to significantly reduce the dark current of ε-Ga2O3 MSM photodetectors by more than three orders of magnitude, and simultaneously enhance the photocurrent and the response speed. With an ultrathin Al2O3 surface layer, the Al2O3/ε-Ga2O3 MSM photodetector achieves a superhigh responsivity of >104 A/W, a detectivity of >1016 Jones with a photo-to-dark ratio of >107, an UV–vis rejection ratio of >104 and millisecond response time for continuous-wave illumination. The surface passivation mechanism is analyzed by combined X-ray photoemission spectroscopy, secondary ion mass-spectroscopy and numerical calculations. It is revealed that the Al2O3 capping layer passivates the surface defects that are in the form of reduced tin species and oxygen vacancies, and reconstructs a faster surface transport channel for more efficient photocarrier collection. This study expands the design concept of surface passivation with ultrawide bandgap semiconductors for developing efficient deep ultraviolet photodetectors.

Sensing performance of β-Ga2O3 metal–semiconductor-metal deep ultraviolet photodetectors with refractory TiW electrodes at high temperatures

Given the critical impact of high-temperature environments on the detection performance and stability of deep ultraviolet (DUV) photonic devices, especially in urgent demands from fields including high-temperature industries and flame detection, the research on high-temperature resistant DUV photodetectors (PDs) has become of utmost importance. Due to its intrinsic high-temperature resistance, β-Ga2O3 holds significant potential in the field of DUV photodetection under elevated temperature environments. The conventional electrode material, titanium, typically exhibits poor high-temperature performance, while interfaces are susceptible to degradation at elevated temperatures. In this study, we fabricated β-Ga2O3 metal–semiconductor-metal (MSM) PDs using the refractory metal TiW as the electrode, and investigated their DUV detection performance across the temperature range of 300 to 800 K. Favorable performance was achieved at room temperature, with a photo-to-dark current ratio (PDCR) of 3.1 × 106, a responsivity (R) of 0.2 A/W, a detectivity (D*) of 8.3 × 1013 Jones, and an external quantum efficiency (EQE) of 102.3 %. However, an increase in operating temperature led to a continuous rise in dark current (Idark) and a decrease followed by an increase in photocurrent (Iphoto). In an 800 K operating environment, the PDCR decreased to 4.4 × 102, R increased to 0.7 A/W, D* dropped to 2.0 × 1012 Jones, and EQE improved to 343.7 %. Furthermore, the temperature-dependent rise and decay times were investigated, and a detailed analysis of the relevant recombination and transport mechanisms under high-temperature conditions was conducted. By achieving high-performance and stable operation of β-Ga2O3 PDs at 800 K, this study provides prospects for the application of β-Ga2O3 PDs in harsh environments.