Deep Ultraviolet Photodetectors Research Articles

Structure Engineering of Ga2O3 photodetectors: A Review

Abstract Deep ultraviolet (DUV) photodetectors play important roles in the modern semiconductor industry due to their diverse applications in critical fields. Wide bandgap semiconductor Ga2O3 is considered as one promising material for highly sensitive DUV photodetectors. However, the high responsivity of Ga2O3 DUV photodetectors always comes at the expense of its response speed. Material engineering for high-quality Ga2O3 materials can optimize the photoresponse performance but at the cost of much more complex process. Structure engineering can efficiently improve the performance of Ga2O3 photodetectors based on various physical mechanisms. Owing to the increased modulation probabilities, part schemes of structure engineering even alleviate the tough requirements on Ga2O3 material quality for high-performance DUV photodetectors. This article reviews the recent efforts in optimizing the performance of Ga2O3 photodetectors through structure engineering. Firstly, photodetectors based on Ga2O3 nanostructures and metasurface structures with nanometer size effect are discussed. In addition, junction structures of Ga2O3 photodetectors, which effectively promote carrier separation in the depletion region, are summarized based on a classification of Schottky junction, heterojunction, phase junction, etc. Besides, Ga2O3 avalanche photodiodes, offering ultra-high gain and responsivity, are focused as a promising prototype for commercialization. Furthermore, field effect phototransistors, based on which the scalability and low power performance of Ga2O3 photodetectors have been well proven, are analyzed in detail. Moreover, auxiliary-field configurations with extra tunable dimensions for Ga2O3 photodetectors are introduced. Finally, we conclude this review and discuss the main challenges of Ga2O3 DUV photodetectors from our perspective.

High-performance deep-ultraviolet photodetector based on a single-crystalline ϵ-Ga2O3/Sn-doped In2O3 heterojunction

Abstract Metastable ϵ-Ga2O3, with its superior physical properties and high substrate compatibility, demonstrates considerable potential in developing heterojunction deep-ultraviolet photodetectors (DUV PDs). Herein, we fabricate a high-performance DUV PD utilizing a single crystalline ϵ-Ga2O3/ Sn-doped In2O3 (ITO) heterojunction. Under a reverse bias of 15 V, the device exhibits a high responsivity of 506 A/W, an excellent UV/visible rejection ratio of 6.74 × 104, and a fast fall time of 40 ms while maintaining good performance across a broad illumination range of 90–4100 μW cm−2. Moreover, the device can operate in a self-powered mode at zero bias, further verifying the presence of a depletion region within the ϵ-Ga2O3/ITO heterojunction. Our results demonstrate that ϵ-Ga2O3 is promising for high-quality integration on ITO and application in DUV detection, offering new strategic directions for developing high-performance Ga2O3-based DUV PDs.

Dressing AgNWs with MXenes Nanosheets: Transparent Printed Electrodes Combining High-Conductivity and Tunable Work Function for High-Performance Opto-Electronics.

High-work function transparent electrodes (HWFTEs) are key for establishing Schottky and Ohmic contacts with n-type and p-type semiconductors, respectively. However, the development of printable materials that combine high transmittance, low sheet resistance, and tunable work function remains an outstanding challenge. This work reports a high-performance HWFTE composed of Ag nanowires enveloped conformally by Ti3C2Tx nanosheets (TA), forming a shell-core network structure. The printed TA HWFTEs display an ultrahigh transmittance (>94%) from the deep-ultraviolet (DUV) to the entire visible spectral region, a low sheet resistance (<15 Ωsq-1), and a tunable work function ranging from 4.7 to 6.0eV. The introduction of additional oxygen terminations on the Ti3C2Tx surface generates positive dipoles, which not only increases the work function of the TA HWFTEs but also elevates the TA/Ga2O3 Schottky barrier, resulting in a high self-powered responsivity of 18mAW-1 in Ga2O3 diode DUV photodetectors, as demonstrated via experimental characterizations and theoretical calculations. Furthermore, the TA HWFTEs-based organic light-emitting transistors exhibit exceptional emission brightness of 5020cd m-2, being four-fold greater than that in Au electrodes-based devices. The innovative nano-structure design, work function tuning, and the revealed mechanisms of electrode-semiconductor contact physics constitute a substantial advancement in high-performance optoelectronic technology.

Performance enhancement of MOCVD grown Zn-doped β-Ga2O3 Deep-Ultraviolet photodetectors on silicon substrates via TiN buffer layers

Integrating β-Ga2O3-based devices on silicon substrates faces challenges due to lattice and thermal expansion mismatches, leading to performance-degrading defects. Therefore, this work explores the utilization of a titanium nitride (TiN) buffer layer in order to enhance the performance of MOCVD grown Zn-doped β-Ga2O3-based deep-ultraviolet (DUV) photodetectors (PDs) on silicon substrates with 12, 24, and 36 sccm diethylzinc (DEZn) flow rates. The XPS depth profiles revealed the presence of TiN buffer layer in β-Ga2O3/TiN/Si films, which served as a diffusion barrier during deposition, preserving interface integrity and reducing defect density. Zn-doped β-Ga2O3/TiN/Si based DUV PDs revealed remarkable results. The 12 sccm Zn-doped β-Ga2O3/TiN/Si PDs demonstrated an exceptional maximum responsivity of 31.4 A/W, which is 7 times higher compared to the undoped β-Ga2O3/TiN/Si (4.47 A/W) under a 5 V bias and 240 nm wavelength illumination. This PD exhibited the detectivity of 1.68 × 1013 Jones and EQE of 1.63 × 104 %. This PD possess quick rise time of 6.5 s and fall time of 0.5 s. The energy band diagram for Zn-doped β-Ga2O3/TiN/Si metal–semiconductor-metal type PDs is discussed. This work demonstrates that TiN buffer layers and Zn doping significantly improve the performance and reliability of β-Ga2O3-based DUV photodetectors on silicon substrates.

Interfacial modification of CuO/Ga2O3 by plasmonic Pt for high performance self-powered solar-blind UV photodetector

Applications for solar-blind photodetectors (PDs) vary widely and include space communications, ozone monitoring, and more. In this study, pulsed laser deposition (PLD) and ion sputtering were employed to develop an unusual self-powered deep ultraviolet (UV) photodetector based on CuO/Ga2O3 with a Pt nanoparticles (NPs) interface. The Pt NPs interface transforms the device design from heterojunction to Schottky junction. The device features a low dark current of 83.2 fA and performs a high photo-to-dark current (Iphoto/Idark) ratio of 1.72 × 104, a specific detectivity (D*) of 9.98 × 1011 Jones, and a quick decay time of 56 ms upon 254 nm UV light at 196.5 μW/cm2 without any power supply. The CuO/Pt/Ga2O3 Schottky junction-based device outperforms the CuO/Ga2O3 heterojunction-based device in terms of detection capabilities in both biased and non-biased settings. This is explained by the Schottky barrier creation mechanism with both Ga2O3 and CuO films, as well as how the plasmon resonance effect (PR effect) balances the barrier on the Ga2O3 side. Furthermore, Pt NPs serve as a potential well, offering an additional recombination channel that accelerates the decay process when the light is turned off. Our findings pave the way for more optoelectronic uses of Ga2O3-based solar-blind UV photodetectors in the future.

Boosting deep-ultraviolet photodetector performance via ferroelectric effect based on HfAlOx@PEI composite

In this study, hafnium-aluminum oxide (HfAlOx) was used as an effective active layer in a self-powered deep-ultraviolet (UV) photodetector. For the first time, we exploited the ferroelectric properties of crystalline HfAlOx to enhance device performance. The HfAlOx powder obtained at an annealing temperature of 850 °C exhibited the highest-intensity peak for the orthorhombic phase (o-phase), representing the ferroelectric property of the material. The HfAlOx particles were reduced to a small size using mechanical treatment to facilitate the preparation of a composite thin film with a polyethyleneimine (PEI) polymer matrix. First, the HfAlOx@PEI composite film-based photodetector demonstrated a remarkable on/off ratio of more than 103 and a rapid response (trise/tfall of 0.127/2.7 s) at zero bias under 254-nm UV illumination. Second, the photocurrent of the device was dramatically boosted under an external bias owing to the injection of carriers, supported by the ferroelectric effect of the o-phase HfAlOx. As a result, the external quantum efficiency and responsivity approached 2628 % and 5.37 A/W at −1 V bias, respectively. Furthermore, the device exhibited excellent photostability, demonstrating almost no change in the photocurrent after 1000 s of UVC irradiation. Our findings provide guidance for the preparation of optoelectronic devices, particularly self-powered high-performance UV photodetectors.

Ultrathin BiOCl crystals grown in highly disordered vapor micro-turbulence for deep ultraviolet photodetectors

Ultrathin BiOCl crystals grown in highly disordered vapor micro-turbulence for deep ultraviolet photodetectors

Localized surface plasmon resonance enhanced deep ultraviolet photodetectors based on Pd@Nb2CTx/AlGaN van der Waals heterojunctions

Localized surface plasmon resonance (LSPR) has been proven as an effective means to improve the performance of optoelectronic devices from infrared to ultraviolet region. However, due to the lack of suitable plasmon materials in the deep ultraviolet (DUV) region, studies in this field were relatively rare. Herein, a simple solution reduction method was proposed to decorate palladium nanoparticles (Pd NPs) onto two-dimensional (2D) niobium carbide Nb2CTx (MXene) nanosheets to fabricate Pd@Nb2CTx/aluminum-gallium nitride (AlGaN) van der Waals heterojunction (vdWH) DUV photodetectors (PDs). Thanks to the plasmon coupling between Pd@Nb2CTx and AlGaN, the obvious enhanced optical absorption and carrier excitation of the as-fabricated DUV PDs have been observed with a peak responsivity of 0.86 A/W, as well as a fast response (rise/decay time of 37.8/14.5 ms) under −3 V bias and 254 nm DUV illumination. This study provides direct evidence for LSPR of Pd NPs in the DUV region, which will develop an optional pathway for the structure design of DUV PDs.

High-performance solar-blind photodetector of β-Ga2O3 grown on sapphire with embedding an ultra-thin AlN buffer layer

The authors reported the MOCVD growth of high-quality β-Ga2O3 on c-plane sapphire substrate, resulting in the achievement of high performance solar blind deep UV photodetectors by introducing an ultra-thin AlN buffer seed layer (BSL). Compared with the direct growth of Ga2O3 on the sapphire, the oxygen vacancy of β-Ga2O3 is reduced after introducing an AlN BSL and the full width at half maximum (FWHM) of (-201) diffraction peak becomes narrower. The dark current is reduced by 1000 times and from 10−10 A down to 10−13 A for the metal-semiconductor-metal planner photodetector of β-Ga2O3 thin film with the AlN BSL. And the detectivity reaches 4.65×1015 cm·Hz1/2·W at 5 V bias. This improvement in performance is derived from the improvement of the growth quality of β-Ga2O3 mediated by the AlN BSL due to the decrease of lattice mismatch. The defects in β-Ga2O3 are reduced, the carrier concentration is reduced, the Fermi level is shifted, the depletion region is widened, the probability of electron tunneling in the dark state is reduced, and the dark current is effectively reduced.

Surface plasmon decorated InGaO deep-UV photodetector array for image sensing and water quality monitoring via highly effective hot electron excitation and interfacial injection

Surface plasmon decorated InGaO deep-UV photodetector array for image sensing and water quality monitoring via highly effective hot electron excitation and interfacial injection

Effect of Methylammonium Iodide (MACl) on MAPbI3-Based Perovskite UV-C Photodetectors

In this study, we fabricated deep ultraviolet (DUV) photodetectors based on perovskite thin films doped with halide materials using formamidinium bromide (FABr) and methylammonium iodide (MAI). The device was fabricated using a simple surface engineering technique by post-treating the MAPbI3 perovskite film with an FABr solution. This film acts as a light absorption layer, like a depletion layer with a p-i-n (PIN) structure, with n-type of SnO2-SDBS and p-type of spiro-OMeTAD. Adding 0.10 M MACl to the MAPbI3 precursor solution during the manufacturing process could effectively reduce the trap density compared with existing films. Films with MACl added in the two-step process can control a wide band gap and improve crystallinity. In addition, the Cl atom has a smaller atomic radius than iodine and a higher electronegativity of 3.16, which can improve phase stability, and the effect of the added Cl− increases the electron mobility of the perovskite, showing a fast response.

High‐Performance Self‐Powered Deep Ultraviolet Photodetector Based on NiO/β‐Ga2O3 Heterojunction with High Responsivity and Selectivity

A high‐performance self‐powered deep ultraviolet (DUV) photodetector based on the NiO/β‐Ga2O3 heterojunction is fabricated and analyzed. The NiO/β‐Ga2O3 heterojunction photodetectors are fabricated both with and without a post‐annealing process following NiO film deposition. Each photodetector structure is investigated through technology computer‐aided design simulations, including energy band diagram, trap density, and carrier concentration. The pristine self‐powered NiO/β‐Ga2O3 photodetector, lacking a post‐annealing process, exhibits partial Schottky contact formation between metal and NiO film, leading to performance degradation, including reduced responsivity, detectivity, and response time. On the other hand, the post‐annealed self‐powered NiO/β‐Ga2O3 photodetector demonstrates high performance such as a responsivity of 592.0 mA W−1, a detectivity of 4.30 × 1012 Jones, and response times of 30.93 ms and 72.32 ms, respectively. Therefore, the fabricated NiO/β‐Ga2O3 photodetector shows a promising potential for various applications requiring DUV detection without an external voltage bias.

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.

Robust Deep UV Photodetectors Based on One‐Step‐Grown Polycrystalline Ga2O3 Film via Pulsed Laser Deposition toward Extreme‐Environment Application

AbstractGallium oxide (Ga2O3), with an ultrawide bandgap corresponding to the deep ultraviolet (DUV) range, has attracted significant attention in optical filter‐free photodetectors. In practical terms, DUV photodetectors employed in extreme conditions, for example, flame detection and space exploration, face the challenges of performance degradation caused by high/low‐temperature transformation. Here, DUV photodetectors are tailored with high durability and stability by one‐step‐grown β‐Ga2O3 films via pulsed laser deposition. A high‐oxygen‐pressure scheme effectively addresses the issue of film‐free deposition at specifically high temperatures, facilitating the formation of polycrystalline high‐resistivity β‐Ga2O3 films. As a result, the devices exhibit outstanding performance, including a low dark current (4.4 pA @30 V), high photoresponsivity (147.36 A W−1), and fast response time (3.1/22.6 ms). Additionally, the photoresponse performance shows minimal degradation at high temperatures up to 300 °C and even improves at low temperatures down to −100 °C, ranking it among the most robust DUV photodetectors. The mechanism of photoresponse, involving the exciton formation, bandgap evolution, carrier‐phonon scatter, etc., is also elucidated in a wide temperature range. This work provides an efficient solution for developing robust Ga2O3 DUV photodetectors with excellent performance for extreme‐condition applications.

Chemical Bath Deposition of ZnO/ZnGa2O4 Core-Shell Nanowire Heterostructures Using Partial Chemical Conversion.

The development of innovative heterostructures made of ZnO nanowires is of great interest for enhancing the performances of many devices in the fields of optoelectronics, photovoltaics, and energy harvesting. We report an original fabrication process to form ZnO/ZnGa2O4 core-shell nanowire heterostructures in the framework of the wet chemistry techniques. The process involves the partial chemical conversion of ZnO nanowires grown via chemical bath deposition into ZnO/ZnGa2O4 core-shell nanowire heterostructures with a high interface quality following their immersion in an aqueous solution containing gallium nitrate heated at a low temperature. The double-step process describing the partial chemical conversion relies on successive dissolution and reaction mechanisms. The present finding offers the possibility to fabricate ZnO/ZnGa2O4 core-shell nanowire heterostructures at low temperatures and over a wide variety of substrates with a large surface area, which is attractive for nanostructured solar cells, deep-UV photodetectors, and piezoelectric devices.

Dynamical stability, electronic and optical properties of AcAlO3 perovskite using mBJ and hybrid functionals: A DFT approach

The structural, elastic, electronic, and optical properties of perovskite AcAlO3 were examined using DFT. First, the dynamical stability of the crystal in the cubic phase was ensured by the phonon dispersion curves. The elastic moduli suggest that the perovskite is mechanically hard and brittle. The 3D elastic moduli surfaces signify moderate elastic anisotropy. To precisely predict the band gaps, the band structures are analyzed using mBJ and YS-PBE0 screened hybrid functionals. Both mBJ and hybrid schemes offer similar band structures with direct band gaps of about 5.6 eV. The optical absorption in the perovskite is prominent in the UV-C region due to the ultra-wide band gap nature and may find suitable application in deep UV 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

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.