Amorphous Ga2O3 Research Articles

Alloying Ga2O3 with Fe2O3 on Corundum‐Structured rh‐ITO by Mist CVD and Its Demonstration of Photodetector and Photoelectrode Applications

Corundum‐structured α‐Ga2O3 is an ultrawide bandgap semiconductor with a bandgap of 5.3 eV and is actively investigated for applications in power electronics and optoelectronic devices. This study explores bandgap engineering of α‐Ga2O3 to broaden its application field. By alloying α‐Fe2O3, which has the same corundum structure as α‐Ga2O3, the bandgap can be tuned from 2.2 to 5.3 eV. This allows α‐Ga2O3 to be used as a visible‐light‐driven photocatalyst by narrowing its bandgap. Herein, (Ga, Fe)2O3 alloy thin films are grown on corundum‐structured indium tin oxide (rh‐ITO) electrodes for photocatalytic applications. X‐ray diffraction 2θ–ω measurements reveal that corundum‐structured α‐(Ga, Fe)2O3 thin films are grown on rh‐ITO electrodes with up to ≈20% Ga composition. At higher Ga compositions, orthorhombic ε‐GaFeO3 and amorphous Ga2O3 are observed on the rh‐ITO electrode. Photoresponsivity measurements using a photodetector structure confirm that the thin films exhibit visible light sensitivity upon alloying Fe2O3 with Ga2O3. Linear sweep voltammetry measurements indicate that the α‐(Ga, Fe)2O3 thin film grown on rh‐ITO can serve as a visible light‐driven photoelectrode. The findings contribute to the bandgap engineering of α‐Ga2O3 and its application in photocatalysis.

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film.

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64×64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Barrier Polarity Reversal Based on Interfacial Modification of Au Nanoparticles for Nonvolatile Multilevel Memory and Optoelectronic Synapses.

Optoelectronic synaptic devices, integrating light sensing and information processing capabilities, have emerged as advantageous tools for the implementation of visual neuromorphic computing. However, the transient light-triggered response characteristic typically results in unstable memory retention times and restricted current response ranges, posing significant challenges to the development and practical application of neural network systems. In response to these limitations, this study developed a nonvolatile optoelectronic memory based on the indium tin oxide (ITO)/Au nanoparticles (NPs)/amorphous Ga2O3 (a-Ga2O3)/Pt structure. Unlike conventional optoelectronic memories, this device features a modification with Au NPs that markedly enhances the Schottky barrier height at the interface. Au NPs function as a charge-trapping layer for sensitive and large-scale modulation of the barrier by the light field, thereby enabling the nonvolatile reversal of the device's barrier polarity. This innovative approach enables controllable multilevel data storage with an ultra large on/off ratio (∼104) and excellent retention capability exceeding 12,000 s. Additionally, the device emulates essential synaptic functions and demonstrates potential application values in visual weak signal perception and image memory. This study introduces a mechanism for Schottky barrier polarity control and presents a promising strategy for the development of future high-performance integrated devices and optoelectronic synaptic elements.

Improved-Performance Amorphous Ga2O3 Photodetectors Fabricated by Capacitive Coupled Plasma-Assistant Magnetron Sputtering

Ga2O3 has received increasing interest for its potential in various applications relating to solar-blind photodetectors. However, attaining a balanced performance with Ga2O3-based photodetectors presents a challenge due to the intrinsic conductive mechanism of Ga2O3 films. In this work, we fabricated amorphous Ga2O3 (a-Ga2O3) metal–semiconductor–metal photodetectors through capacitive coupled plasma assisted magnetron sputtering at room temperature. Substantial enhancement in the responsivity is attained by regulating the capacitance-coupled plasma power during the deposition of a-Ga2O3. The proposed plasma energy generated by capacitive coupled plasma (CCP) effectively improved the disorder of amorphous Ga2O3 films. The results of X-ray photoelectron spectroscopy (XPS) and current-voltage tests demonstrate that the additional plasma introduced during the sputtering effectively adjust the concentration of oxygen vacancy effectively, exhibiting a trade-off effect on the performance of a-Ga2O3 photodetectors. The best overall performance of a-Ga2O3 photodetectors exhibits a high responsivity of 30.59 A/W, a low dark current of 4.18 × 10−11, and a decay time of 0.12 s. Our results demonstrate that the introduction of capacitive coupled plasma during deposition could be a potential approach for modifying the performance of photodetectors.

High ultraviolet gain in Ga2O3/ZnO heterojunction photodetector based on MSM structure

Amorphous Ga2O3 (a-Ga2O3) has attracted extensive attention due to its simple preparation process and low cost, but the extension of photoelectron lifetime caused by the trap state inhibits the responsiveness of a-Ga2O3 photodetector (PD), and how to improve the ultraviolet (UV) gain of a-Ga2O3 based PD is still a challenge. In this study, an a-Ga2O3/ZnO heterojunction PD based on metal-semiconductor-metal (MSM) structure was designed and fabricated by radio frequency magnetron sputtering (RFMS), and a high-concentration electron transport channel was formed by using carrier multiplication and specific band structure in the high-field region of MSM structure, which achieved high optical gain and extraordinary optical detection ability. In the UVC-UVA band, the device has a peak responsivity of 1.59 A W−1 and a high light-dark ratio, EQE and D* of 1×104, 647 % and 3.6×1012 Jones under 5 V, respectively. In particular, compared to ZnO PD and a-Ga2O3 PD, the responsivity of the device is improved by a factor of 21 and 90, respectively. This study provides a new and effective method for the significant improvement of a-Ga2O3 based UV photoelectric detection performance.

Ultrasensitive Self-Powered Flexible Crystalline β-Ga2O3-Based Photodetector Obtained through Lattice Symmetry and Band Alignment Engineering.

Due to its portable and self-powered characteristics, the construction of Ga2O3-based semiconductor flexible devices that can improve the adaptability in various complex environments have drawn great attention in recent decades. However, conventional Ga2O3-based flexible heterojunctions are based on either amorphous or poor crystalline Ga2O3 materials, which severely limit the performance of the corresponding devices. Here, through lattice-symmetry and energy-band alignment engineering, we construct a high-quality crystalline flexible NiO/β-Ga2O3 p-n self-powered photodetector. Owing to its suitable energy-band alignment structure, the device shows a high photo-to-dark current ratio (1.71 × 105) and a large detection sensitivity (6.36 × 1014 Jones) under zero bias, which is superior than most Ga2O3 self-powered photodetectors even for those based on rigid substrates. Moreover, the fabricated photodetectors further show excellent mechanical stability and robustness in bending conditions, demonstrating their potential practical applications in flexible optoelectronic devices. These findings provide insights into the manipulation of crystal lattice and energy band engineering in flexible self-powered photodetectors and also offer guideline for designing other Ga2O3-based flexible electronic devices.

Improvements in Resistive and Capacitive Switching Behaviors in Ga2O3 Memristors via High-Temperature Annealing Process.

This study investigates the effect of a high-temperature annealing process on the characteristics and performance of a memristor based on a Ag/Ga2O3/Pt structure. Through X-ray diffraction analysis, successful phase conversion from amorphous Ga2O3 to β-Ga2O3 is confirmed, attributed to an increase in grain size and recrystallization induced by annealing. X-ray photoelectron spectroscopy analysis revealed a higher oxygen vacancy in annealed Ga2O3 thin films, which is crucial for conductive filament formation and charge transport in memristors. Films with abundant oxygen vacancies exhibit decreased set voltages and increased capacitance in a low-resistive state, enabling easy capacitance control depending on channel presence. In addition, an excellent memory device with a high on/off ratio can be implemented due to the reduction of leakage current due to recrystallization. Therefore, it is possible to manufacture a thin film suitable for a memristor by increasing the oxygen vacancy in the Ga2O3 film while improving the overall crystallinity through the annealing process. This study highlights the significance of annealing in modulating capacitance and high-resistive/low-resistive state properties of Ga2O3 memristors, contributing to optimizing device design and performance. This study underscores the significance of high-temperature annealing in improving the channel-switching characteristics of Ga2O3-based memristors, which is crucial for the development of low-power, high-efficiency memory device.

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 %.

Mixed‐Dimensional 2D PtSe2/3D a‐Ga2O3 Heterojunction for Self‐Driven Broadband Photodetector with High Responsivity in UV Region

Self‐driven broadband photodetectors have wide applications in the fields of biomedicine, remote sensing, rescue, and mineral exploration with advantages of energy conservation and multiband detection. However, most present broadband photodetectors are suffering from a fast degradation of photoresponsivity in ultraviolet (UV) region. To resolve it, a self‐driven broadband photodetector is proposed based on mixed‐dimensional 2D PtSe2/3D amorphous Ga2O3 (a‐Ga2O3) heterojunction considering the high UV responsivity of a‐Ga2O3 thin film. 2D PtSe2 is obtained on a‐Ga2O3 thin film by a simple selenization method directly. The responsivity of the completed device in UV region is about 14 and 172 times higher than that in visible and NIR regions, respectively. In addition, benefiting from the excellent built‐in electric field at the heterojunction and high carrier mobility of 2D PtSe2, photogenerated electron–hole pairs can be rapidly separated. As a result, its rise time (9.36 ms) and decay time (11.27 ms) are much faster than those of the current a‐Ga2O3‐based self‐driven photodetectors (≈100–1000 ms). This work provides a novel building block via a facile strategy for the further development of high‐performance, low‐cost, and energy‐efficient broadband photodetectors.

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

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

Nanopatterning Induced Si Doping in Amorphous Ga2O3 for Enhanced Electrical Properties and Ultra-Fast Photodetection.

Ga2O3 has emerged as a promising material for the wide-bandgap industry aiming at devices beyond the limits of conventional silicon. Amorphous Ga2O3 is widely being used for flexible electronics, but suffers from very high resistivity. Conventional methods of doping like ion implantation require high temperatures post-processing, thereby limiting their use. Herein, an unconventional method of doping Ga2O3 films with Si, thereby enhancing its electrical properties, is reported. Ion-beam sputtering (500eV Ar+) is utilized to nanopattern SiO2-coated Si substrate leaving the topmost part rich in elemental Si. This helps in enhancing the carrier conduction by increasing n-type doping of the subsequently coated 5nm amorphous Ga2O3 films, corroborated by room-temperature resistivity measurement and valence band spectra, respectively, while the nanopatterns formed help in better light management. Finally, as proof of concept, metal-semiconductor-metal (MSM) photoconductor devices fabricated on doped, rippled films show superior properties with responsivity increasing from 6 to 433mAW-1 while having fast detection speeds of 861µs/710µs (rise/fall time) as opposed to non-rippled devices (377ms/392ms). The results demonstrate a facile, cost-effective, and large-area method to dope amorphous Ga2O3 films in a bottom-up approach which may be employed for increasing the electrical conductivity of other amorphous oxide semiconductors as well.

The Impact of the Amorphous-to-Crystalline Transition on the Upconversion Luminescence in Er3+-Doped Ga2O3 Thin Films

Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor promising a wide range of important applications. However, mass production of high-quality crystalline Ga2O3 still suffers from limitations associated with poor reproducibility and low efficiency. Low-temperature-grown amorphous Ga2O3 demonstrates comparable performance with its crystalline counterparts. Lanthanide Er3+-doped Ga2O3 (Ga2O3: Er) possesses great potential for developing light-emitting devices, photodetectors, solid-state lasers, and optical waveguides. The host circumstance can exert a crystal field around the lanthanide dopants and strongly influence their photoluminescence properties. Here, we present a systematical study of the impact of amorphous-to-crystalline transition on the upconversion photoluminescence in Ga2O3: Er thin films. Through controlling the growth temperature of Ga2O3: Er films, the upconversion luminescence of crystalline Ga2O3: Er thin film is strongly enhanced over 100 times that of the amorphous Ga2O3: Er thin film. Moreover, the variation of photoluminescence reflects the amorphous-to-crystalline transformation of the Ga2O3: Er thin films. These results will aid further designs of favorable optoelectronic devices integrated with lanthanide-doped Ga2O3 thin films.

Boosting the responsivity of amorphous-Ga2O3 solar-blind photodetector via organosilicon surface passivation

In this paper, an amorphous Ga2O3 metal–semiconductor–metal photodetectors passivated by the organosilicon layer were reported. Due to the excellent passivation property of the passivation layer and the diffusion effect of hydrogen, the responsivity of Ga2O3 photodetectors was improved effectively, while the dark state current is basically unchanged. The results of x-ray photoelectron spectroscopy have proved that the amount of oxygen vacancy near the interface between organosilicon and Ga2O3 layer has been passivated and the surface chemisorption was suppressed via capping a foreign layer after the deposition of organosilicon passivation layer. The Ga2O3 photodetectors with organosilicon passivation layer exhibit a boosted performance, with a low dark current of 2.96 × 10−12 A, a responsivity of 11.82 A/W, and a specific detectivity of 9.01 × 1014 Jones.

Flexible UV detectors based on in-situ hydrogen doped amorphous Ga2O3 with high photo-to-dark current ratio

Amorphous Ga2O3 (a-Ga2O3) has been attracting more and more attention due to its unique merits such as wide bandgap (∼4.9 eV), low growth temperature, large-scale uniformity, low cost and energy efficient, making it a powerful competitor in flexible deep ultraviolet (UV) photodetection. Although the responsivity of the ever-reported a-Ga2O3 UV photodetectors (PDs) is usually in the level of hundreds of A/W, it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy (V O) defects, which severely limits the possibility to detect weak signals and achieve versatile applications. In this work, the V O defects in a-Ga2O3 thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process. As a result, the dark current of a-Ga2O3 UV PD is remarkably suppressed to 5.17 × 10−11 A at a bias of 5 V. Importantly, the photocurrent of the corresponding device is still as high as 1.37 × 10−3 A, leading to a high photo-to-dark current ratio of 2.65 × 107 and the capability to detect the UV light with the intensity below 10 nW cm−2. Moreover, the H-doped a-Ga2O3 thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs, which exhibit no great degradation in bending states and fatigue tests. These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga2O3 UV PDs, further promoting its practical application in various areas.

Enhancing plasticity in optoelectronic artificial synapses: A pathway to efficient neuromorphic computing

The continuous growth in artificial intelligence and high-performance computing has necessitated the development of efficient optoelectronic artificial synapses crucial for neuromorphic computing (NC). Ga2O3 is an emerging wide-bandgap semiconductor with high deep ultraviolet absorption, tunable persistent photoconductivity, and excellent stability toward electric fields, making it a promising component for optoelectronic artificial synapses. Currently reported Ga2O3 optoelectronic artificial synapses often suffer from complex fabrication processes and potential room for improvement due to plasticity. To address the issue of low device plasticity and practical application scenarios, we present an amorphous Ga2O3 (α-GaOx) flexible optoelectronic artificial synapse. This synapse modulates light stimulus signals using electron/oxygen vacancies and optical stimulation and operates as a visual storage device for information processing. We investigate the improvement of the optoelectronic synapses' plasticity by controlling the number of oxygen vacancies via a plasma treatment method and demonstrate its effective application in a three-layer backpropagation neural network for handwritten digit classification. Under the same stimulus conditions, the synaptic weight of samples treated with Ar plasma exhibits a higher rate of change, with the current levels increasing by 2–3 orders of magnitude, achieving greater plasticity. The improved optoelectronic synapses achieved an accuracy of 93.34%/94%, demonstrating their potential as efficient computing solutions and insights for future applications in NC chips.

Influence of annealing pretreatment in different atmospheres on crystallization quality and UV photosensitivity of gallium oxide films.

Due to their high wavelength selectivity and strong anti-interference capability, solar-blind UV photodetectors hold broad and important application prospects in fields like flame detection, missile warnings, and secure communication. Research on solar-blind UV detectors for amorphous Ga2O3 is still in its early stages. The presence of intrinsic defects related to oxygen vacancies significantly affects the photodetection performance of amorphous Ga2O3 materials. This paper focuses on growing high quality amorphous Ga2O3 films on silicon substrates through atomic layer deposition. The study investigates the impact of annealing atmospheres on Ga2O3 films and designs a blind UV detector for Ga2O3. Characterization techniques including atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used for Ga2O3 film analysis. Ga2O3 films exhibit a clear transition from amorphous to polycrystalline after annealing, accompanied by a decrease in oxygen vacancy concentration from 21.26% to 6.54%. As a result, the response time of the annealed detector reduces from 9.32 s to 0.47 s at an external bias of 10 V. This work demonstrates that an appropriate annealing process can yield high-quality Ga2O3 films, and holds potential for advancing high-performance solar blind photodetector (SBPD) development.

Unraveling the atomic mechanism of the disorder–order phase transition from γ-Ga2O3 to β-Ga2O3

In this paper, we employ in situ transmission electron microscopy to study the disorder–order phase transition from amorphous Ga2O3 to γ-Ga2O3 and then to β-Ga2O3. The in situ studies are complemented by ex situ annealing experiments, of which the results are analyzed by x-ray diffraction and high resolution (scanning) transmission electron microscopy. Amorphous Ga2O3 deposited at 100 °C by molecular beam epitaxy crystallizes at 470 °C in the γ phase (Fd3̄m), which undergoes a phase transition to the β phase above 500 °C. Between 500° and 900 °C, we find a mixture of γ-Ga2O3 and β-Ga2O3 coexisting. Above 950 °C, we find only β-Ga2O3. Through our analyses and by considering symmetry relations, we have constructed a coincidence site lattice of both structures containing a common fcc-type sublattice occupied by oxygen atoms, the cation sites of β-Ga2O3 common to both phases, and partially occupied cation sites in the γ phase corresponding to the interstitial sites in the β phase. We assign the atomic displacements within this lattice responsible for transforming the initially disordered spinel structure with partially occupied cation sites into the well-ordered lattice of β-Ga2O3. We identify this transition as a reconstructive disorder-to-order phase transition, mediated by the exchange of cations to next nearest neighbor sites. Our model not only explains recent observations of the formation of γ-Ga2O3 during implantation for n-type doping and the subsequent recovery of β-Ga2O3 following annealing but also holds potential for inspiring understanding in other materials with similar phase transitions.

Optical properties of Ga2O3 thin films grown by atomic layer deposition using GaI3 and O3 as precursors

Absorption spectra, bandgap energies, refractive indices, and antireflection properties of atomic-layer-deposited amorphous Ga2O3, κ/ε-Ga2O3, and α-Ga2O3 films were Investigated.

Photoresponse of large-area atomically thin β-Ga2O3 and GaN materials via liquid metal print synthesized

This study uses liquid gallium metal to synthesize two-dimensional gallium oxide and gallium nitride ultra-thin layers. Addressing the challenges of conventional methods, this approach combines liquid metal properties with Polydimethylsiloxane (PDMS) transfer printing, resulting in large-area, highly clean, and low-residue amorphous Ga-based wide bandgap semiconductors. Transformation of amorphous Ga2O3 into crystallized β-Ga2O3 and GaN is achieved through annealing and ammoniation. Comprehensive characterizations confirm successful changes. Photodetector devices are fabricated and characterized, revealing Ga2O3 photosensitive nature with distinct performance metrics. GaN, while exhibiting lower photoresponse, displays rapid photocurrent recovery, making it promising for photodetector applications. This research offers a scalable method for two-dimensional gallium-group semiconductor synthesis, holding potential for diverse optoelectronic applications.

Multifunctional solar‐blind ultraviolet photodetectors based on p‐PCDTBT/n‐Ga2O3 heterojunction with high photoresponse

AbstractSolar‐blind ultraviolet (UV) photodetectors based on p‐organic/n‐Ga2O3 hybrid heterojunctions have attracted extensive attention recently. Herein, the multifunctional solar‐blind photodetector based on p‐type poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT)/n‐type amorphous Ga2O3 (a‐Ga2O3) is fabricated and investigated, which can work in the phototransistor mode coupling with self‐powered mode. With the introduction of PCDTBT, the dark current of such the a‐Ga2O3‐based photodetector is decreased to 0.48 pA. Meanwhile, the photoresponse parameters of the a‐Ga2O3‐based photodetector in the phototransistor mode to solar‐blind UV light are further increased, that is, responsivity (R), photo‐detectivity (D*), and external quantum efficiency (EQE) enhanced to 187 A W–1, 1.3 × 1016 Jones and 9.1 × 104 % under the weak light intensity of 11 μW cm–2, respectively. Thanks to the formation of the built‐in field in the p‐PCDTBT/n‐Ga2O3 type‐II heterojunction, the PCDTBT/Ga2O3 multifunctional photodetector shows self‐powered behavior. The responsivity of p‐PCDTBT/n‐Ga2O3 multifunctional photodetector is 57.5 mA W–1 at zero bias. Such multifunctional p‐n hybrid heterojunction‐based photodetectors set the stage for realizing high‐performance amorphous Ga2O3 heterojunction‐based photodetectors.image