Ultrathin Ga2O3 Research Articles

Ultrathin Ga2O3 Photodetector with Fast Response and Trajectory Tracking Capability Fabricated by Liquid Metal Oxidation.

Low-dimensional Ga2O3 demonstrates a unique ultraviolet photoresponse and could be used in various electronic and optical systems. However, the low-dimensional Ga2O3 photodetector is faced with the challenges of a complex preparation process and poor device performance. In this work, ultrathin Ga2O3 layers with ∼7 nm thickness are prepared on quartz rods by UV exposure to liquid gallium. Benefiting from low-density oxygen vacancy defects cured by UV exposure, the low-dimensional Ga2O3 photodetector exhibits a high response speed (rise: 64.7 μs; fall: 51.4 μs) and an exceptional linear dynamic range of 120 dB. Furthermore, the photodetector array based on these ultrathin Ga2O3 shows an effective trajectory tracking capability by monitoring UV source motion. This work develops a simple preparation method to construct a low-dimensional UV photodetector array with fast response and useful trajectory tracking capability, exhibiting the significance of ultrathin Ga2O3 in UV optoelectronics.

Hybrid mode for absorption enhancement in the Ga2O3 nanocavity photodetector with grating electrodes

Gallium oxide (Ga2O3) photodetectors have drawn increased interest for their widespread applications ranging from military to civil. Due to the inherent oxygen vacancy defects, they seriously suffer from trade-offs that make them incompetent for high-responsivity, quick-response detection. Herein, a Ga2O3 nanocavity photodetector assisted with grating electrodes is designed to break the constraint. The proposed structure supports both the plasmonic mode and the Fabry–Perot (F-P) mode. Numerical calculations show that the absorption of 99.8% is realized for ultra-thin Ga2O3 (30 nm), corresponding to a responsivity of 12.35 A/W. Benefiting from optical mechanisms, the external quantum efficiency (EQE) reaches 6040%, which is 466 times higher than that of bare Ga2O3 film. Furthermore, the proposed photodetector achieves a polarization-dependent dichroism ratio of 9.1, enabling polarization photodetection. The grating electrodes also effectively reduce the transit time of the photo-generated carriers. Our work provides a sophisticated platform for developing high-performance Ga2O3 photodetectors with the advantages of simplified fabrication processes and multidimensional detection.

Interface Properties of MoS2 van der Waals Heterojunctions with GaN.

The combination of the unique physical properties of molybdenum disulfide (MoS2) with those of gallium nitride (GaN) and related group-III nitride semiconductors have recently attracted increasing scientific interest for the realization of innovative electronic and optoelectronic devices. A deep understanding of MoS2/GaN interface properties represents the key to properly tailor the electronic and optical behavior of devices based on this heterostructure. In this study, monolayer (1L) MoS2 was grown on GaN-on-sapphire substrates by chemical vapor deposition (CVD) at 700 °C. The structural, chemical, vibrational, and light emission properties of the MoS2/GaN heterostructure were investigated in detail by the combination of microscopic/spectroscopic techniques and ab initio calculations. XPS analyses on as-grown samples showed the formation of stoichiometric MoS2. According to micro-Raman spectroscopy, monolayer MoS2 domains on GaN exhibit an average n-type doping of (0.11 ± 0.12) × 1013 cm-2 and a small tensile strain (ε ≈ 0.25%), whereas an intense light emission at 1.87 eV was revealed by PL analyses. Furthermore, a gap at the interface was shown by cross-sectional TEM analysis, confirming the van der Waals (vdW) bond between MoS2 and GaN. Finally, density functional theory (DFT) calculations of the heterostructure were carried out, considering three different configurations of the interface, i.e., (i) an ideal Ga-terminated GaN surface, (ii) the passivation of Ga surface by a monolayer of oxygen (O), and (iii) the presence of an ultrathin Ga2O3 layer. This latter model predicts the formation of a vdW interface and a strong n-type doping of MoS2, in closer agreement with the experimental observations.

Thermal mismatch engineering induced freestanding and ultrathin Ga2O3 membrane for vertical electronics

Inevitable thermal-expansion-coefficient mismatch at the interface of epitaxial-layer/foreign-substrate is generally considered as a weak side since considerable strain would be induced during the temperature ramping process. However, rather than the conventional strain minimizing strategy, engineering this thermal-induced strain, i.e., beyond the tolerance of the interfacial bond energy, may result in the exfoliation of the epitaxial layer from bulk substrate. In this work, Ga2O3 membrane, a promising and desirable material for deep ultraviolet (DUV) photonics and high-power electronics, could be exfoliated from a pre-deposited Si-doped Ga2O3/AlN template in a high-temperature environment, allowing the vertical device configuration and preferable thermal management regardless of the costly Ga2O3 substrates. The exfoliated Ga2O3 membrane, which is comparable to the commercial Ga2O3 substrates, is freestanding, centimeter-scale, but ultrathin. The exfoliated Ga2O3 membrane was applied to a vertical DUV photodetector, which demonstrated an on/off ratio of 4.20 × 104, responsivity of 170.3 A/W, and detectivity of 1.01 × 1013 Jones under 254 nm illumination at a bias of −5 V. The presented thermal mismatch engineering (TME) would allow researchers to look beyond the hetero-mismatch and unitize the interfacial strain for membrane exfoliation, e.g., freestanding Ga2O3 membrane for vertical electronics that avoid the ongoing high-cost native substrates.

Liquid-Metal-Printed Ultrathin Oxides for Atomically Smooth 2D Material Heterostructures.

Two-dimensional (2D) semiconductors are promising channel materials for continued downscaling of complementary metal-oxide-semiconductor (CMOS) logic circuits. However, their full potential continues to be limited by a lack of scalable high-k dielectrics that can achieve atomically smooth interfaces, small equivalent oxide thicknesses (EOTs), excellent gate control, and low leakage currents. Here, large-area liquid-metal-printed ultrathin Ga2O3 dielectrics for 2D electronics and optoelectronics are reported. The atomically smooth Ga2O3/WS2 interfaces enabled by the conformal nature of liquid metal printing are directly visualized. Atomic layer deposition compatibility with high-k Ga2O3/HfO2 top-gate dielectric stacks on a chemical-vapor-deposition-grown monolayer WS2 is demonstrated, achieving EOTs of ∼1 nm and subthreshold swings down to 84.9 mV/dec. Gate leakage currents are well within requirements for ultrascaled low-power logic circuits. These results show that liquid-metal-printed oxides can bridge a crucial gap in dielectric integration of 2D materials for next-generation nanoelectronics.

2D graphitic-like gallium nitride and other structural selectivity in confinement at the graphene/SiC interface

An atomic resolution image of an intercalated structure at a graphene/SiC interface along the growth direction which is determined as a buckled GaN monolayer at the immediate interface with an underlying SiC substrate and ultrathin Ga2O3 on top.

Engineering of Oxide Protected Gold Nanoparticles.

Gold nanoparticles that are partially or fully covered by metal oxide shells provide superior functionality and stability for catalytic and plasmonic applications. Yet, facile methods for controlled fabrication of thin oxide layers on metal nanoparticles are lacking. Here, we report an easy method to reliably engineer thin Ga2O3 shells on Au nanoparticles, based on liquid-phase chemical oxidation of Au-Ga alloy nanoparticles. We demonstrate that, with this technique, laminar and ultrathin Ga2O3 shells can be grown with ranging thickness from sub- to several monolayers. We show how the localized surface plasmon resonance can be used to understand the reaction process and quantitatively monitor the Ga2O3 shell growth. Finally, we demonstrate that the Ga2O3 coating prevents sintering of the Au nanoparticles, providing thermal stability to at least 250 °C. This approach, building on dealloying of bimetallic nanoparticles by the solution-phase oxidation, promises a general technique for achieving controlled metal/oxide core/shell nanoparticles.

Aqueous‐Printed Ga2O3 Films for High‐Performance Flexible and Heat‐Resistant Deep Ultraviolet Photodetector and Array

AbstractHigh deep‐ultraviolet (DUV) sensitivity and excellent flexibility of ultrathin gallium oxide (Ga2O3) film with an ultrawide bandgap endow its extreme propensity in flexible DUV photodetector especially for space exploration and wearable electronics. However, an efficient strategy with high throughput and low cost is highly deficient to realize flexible and robust Ga2O3 DUV photodetectors to face potential harsh environments. In this work, flexible and heat‐resistant Ga2O3 DUV photodetectors based on optimized inkjet printing with environmental‐friendly aqueous solvent are demonstrated. The dynamic evolution from Ga(NO3)3 precursor to crystalline Ga2O3 film has been explicitly uncovered. Photodetectors based on printed ultrathin Ga2O3 films on rigid substrate exhibit outstanding performance, including high photo‐to‐dark current ratio about 106, considerable responsivity of 1.3 A W−1, superior detectivity of 1.46 × 1014 Jones, and fast decay time of 0.026 s under 254 nm illumination. In addition, flexible devices on mica substrate not only retain outstanding photoelectrical performance, but also demonstrate excellent mechanical flexibility and thermal stability. Moreover, benefiting from the uniformity of the pixels by high‐throughput inkjet printing, the Ga2O3 DUV photodetector array presents excellent sharp‐imaging capability. This work provides a feasible strategy for printable, flexible, and harsh‐environment‐resistant Ga2O3 DUV photodetectors toward space exploration and wearable electronics.

Controlled growth of 2D ultrathin Ga2O3 crystals on liquid metal.

2D metal oxides (2DMOs) have drawn intensive interest in the past few years owing to their rich surface chemistry and unique electronic structures. Striving for large-scale and high-quality novel 2DMOs is of great significance for developing future nano-enabled technologies. In this work, we demonstrate for the first time controllable growth of highly crystalline 2D ultrathin Ga2O3 single crystals on liquid Ga by the chemical vapor deposition approach. With the introduction of oxygen into the growth process, large-area hexagonal α-Ga2O3 crystals with a uniform size distribution have been produced. At high temperature, fast diffusion of oxygen atoms onto the liquid surface facilitates reaction with Ga and thus leads to in situ formation of 2D ultrathin crystals. By precisely controlling the amount of oxygen, the vertical growth of the Ga2O3 single crystal has been realized. Furthermore, phase engineering can be achieved and thus 2D β-Ga2O3 crystals were also prepared by precisely tuning the growth temperature. The controlled growth of 2D Ga2O3 crystals offers an applicable avenue for fabrication of other 2D metal oxides and can further open up possibilities for future electronics.

Ultrathin Ga2 O3 Glass: A Large-Scale Passivation and Protection Material for Monolayer WS2.

Atomically thin transition metal dichalcogenide crystals (TMDCs) have extraordinary optical properties that make them attractive for future optoelectronic applications. Integration of TMDCs into practical all-dielectric heterostructures hinges on the ability to passivate and protect them against necessary fabrication steps on large scales. Despite its limited scalability, encapsulation of TMDCs in hexagonal boron nitride (hBN) currently has no viable alternative for achieving high performance of the final device. Here, it is shown that the novel, ultrathin Ga2 O3 glass is an ideal centimeter-scale coating material that enhances optical performance of the monolayers and protects them against further material deposition. In particular, Ga2 O3 capping of monolayer WS2 outperforms commercial-grade hBN in both scalability and optical performance at room temperature. These properties make Ga2 O3 highly suitable for large-scale passivation and protection of monolayer TMDCs in functionalheterostructures.

Investigation in the Ga2O3 passivation layer formed as GaN Schottky barrier through UV/O3 treatment

Passivation capability of ultrathin Ga2O3 surface layer formed on GaN through ultraviolet/ozone (UV/O3) treatment is assessed with an exploration of conduction in GaN Schottky diode (SD). The physical and chemical features of ultrathin oxide layer are analyzed to examine the crystalline property. The passivation of dislocation-related structures by UV/O3 treatment improves the conduction in GaN SD.

Precise control of the microstructural, optical, and electrical properties of ultrathin Ga2O3 film through nanomixing with few atom-thick SiO2 interlayer via plasma enhanced atomic layer deposition

Ultrathin Ga2O3 films nanomixed with few atom-thick SiO2 interlayer were deposited on silicon and quartz substrates through plasma-enhanced atomic layer deposition.

Self-limiting growth of ultrathin Ga2O3 for the passivation of Al2O3/InGaAs interfaces

Ga2O3 film growth on InGaAs substrates was investigated using an atomic layer deposition system with trimethylgallium (TMGa) and H2O as precursors. Self-limiting growth of Ga2O3 was confirmed on InGaAs substrates as well as on Si and GaAs. During initial formation of the Ga2O3 film on an InGaAs substrate, the selective self-cleaning effect of TMGa on AsOx and GaOx was observed. The insertion of ultrathin Ga2O3 into an Al2O3/InGaAs gate stack as an interfacial passivation layer proved quite effective to reduce Dit around the midgap. The Al2O3/InGaAs MISFET performance also revealed improvement of the effective mobility for both NH4OH- and (NH4)2S-treated devices.

A Ga2O3underlayer as an isomorphic template for ultrathin hematite films toward efficient photoelectrochemical water splitting

Hematite photoanodes for photoelectrochemical (PEC) water splitting are often fabricated as extremely-thin films to minimize charge recombination because of the short diffusion lengths of photoexcited carriers. However, poor crystallinity caused by structural interaction with a substrate negates the potential of ultrathin hematite photoanodes. This study demonstrates that ultrathin Ga2O3 underlayers, which were deposited on conducting substrates prior to hematite layers by atomic layer deposition, served as an isomorphic (corundum-type) structural template for ultrathin hematite and improved the photocurrent onset of PEC water splitting by 0.2 V. The benefit from Ga2O3 underlayers was most pronounced when the thickness of the underlayer was approximately 2 nm. Thinner underlayers did not work effectively as a template presumably because of insufficient crystallinity of the underlayer, while thicker ones diminished the PEC performance of hematite because the underlayer prevented electron injection from hematite to a conductive substrate due to the large conduction band offset. The enhancement of PEC performance by a Ga2O3 underlayer was more significant for thinner hematite layers owing to greater margins for improving the crystallinity of ultrathin hematite. It was confirmed that a Ga2O3 underlayer was applicable to a rough conducting substrate loaded with Sb-doped SnO2 nanoparticles, improving the photocurrent by a factor of 1.4. Accordingly, a Ga2O3 underlayer could push forward the development of host-guest-type nanocomposites consisting of highly-rough substrates and extremely-thin hematite absorbers.

パルスレーザー堆積法により作製したアルミドープ酸化亜鉛透明導電膜の超薄膜化

Ultra-thin Ga2O3 doped zinc oxide transparent conduction films was deposited on glass substrates using pulsed laser deposition method by ArF excimer laser (λ=193 nm) at the substrate temperature from 180 to 260 °C. The film thickness was changed from 40 to 110 nm-thick. The target containing 3 and 5 wt.% Ga2O3 were employed. As a result, resistivity of 2.69×10−4 Ω·cm was obtained for the film with 40 nm-thick fabricated using the target containing 5 wt.% Ga2O3 at substrate temperature of 260°C.