High-Performance Solar-Blind Photodetector Based on (010)-Plane β-Ga2O3 Thermally Oxidized from Nonpolar (110)-Plane GaN

A high-performance planar structure metal-semiconductor-metal-type solar-blind photodetector (SBPD) was fabricated on the basis of (010)-plane β-Ga2O3 thermally oxidized from nonpolar (110)-plane GaN. A full width at half maximum of 0.486° was achieved for the X-ray rocking curve associated with (020)-plane β-Ga2O3, which is better than most reported results for the heteroepitaxially grown (-201)-plane β-Ga2O3. As a result of the relatively high crystalline quality, a dark current as low as 6.30 × 10-12 A was achieved at 5 V, while the photocurrent reached 1.86 × 10-5 A under 254 nm illumination at 600 μW/cm2. As a result, the photo-to-dark current ratio, specific detectivity, responsivity, and external quantum efficiency were calculated to be 2.95 × 106, 2.39 × 1012 Jones, 3.72 A/W, and 1815%, respectively. Moreover, the SBPD showed excellent repeatability and stability in the time-dependent photoresponse characteristics with fast relaxation time constants for the rise and decay processes of only 0.238 and 0.062 s, respectively. This study provides a promising approach to fabricate the device-level (010)-plane β-Ga2O3 film and a new way for the epitaxial growth of (010)-plane β-Ga2O3 and (110)-plane GaN as mutual substrates.

Ultrafast Multifunctional Photodetector Based on the NiAl2O4/4H-SiC Heterojunction

Solar-blind photodetectors based on wide bandgap semiconductors have recently attracted a lot of interest. Nickel-containing spinel phase oxides, such as NiAl2O4, are stable p-type semiconductors. This paper describes a multifunctional solar-blind photodetector based on a NiAl2O4/4H-SiC heterojunction that utilizes photovoltaic effects. The position sensitivity reaches a value of 1589.7 mV/mm under 405 nm laser illumination, while the relaxation times of vertical photovoltaic (VPV) effect and lateral photovoltaic (LPV) effect under 266 nm laser illumination are only 0.32 and 0.42 μs, respectively. This junction was used to create a space optical communication system with sunlight having little effect on its optoelectronic properties. The ultrafast photovoltaic relaxation time makes NiAl2O4/4H-SiC a promising candidate for self-powered high-performance solar-blind detectors.

Over 5 × 103-Fold Enhancement of Responsivity in Ga2O3-Based Solar Blind Photodetector via Acousto-Photoelectric Coupling

The emergence of the wide-band-gap semiconductor Ga2O3 has propelled it to the forefront of solar blind detection activity owing to its key features. Although various architectures and designs of Ga2O3-based solar blind photodetectors have been proposed, their performance still falls short of commercial standards. In this study, we demonstrate a method to enhance the performance of a simple metal-semiconductor-metal-structured Ga2O3-based solar blind photodetector by exciting acoustic surface waves. Specifically, we demonstrate that under a bias voltage of 100 mV and a radio frequency signal of 20 dBm, the responsivity and detectivity can increase from 2.78 to 1.65 × 104 A/W and from 8.35 × 1014 to 2.66 × 1016 jones, respectively, rivaling a commercial photomultiplier tube. The over 5 × 103-fold enhancement in responsivity could be attributed to the acousto-photoelectric coupling mechanism. Furthermore, since surface acoustic waves can also serve as signal receivers, such photodetectors offer the prospect of dual-mode detection. Our findings reveal a promising pathway for achieving high-performance Ga2O3-based electronics and optoelectronics.

Efficient Suppression of Persistent Photoconductivity in β-Ga2O3-Based Photodetectors with Square Nanopore Arrays

In this work, square nanopore arrays were developed on the surface of β-Ga₂O₃ microflakes using focused ion beam (FIB) etching, and solar-blind photodetectors (PDs) were fabricated based on the β-Ga₂O₃ microflakes with square nanopore arrays. The β-Ga₂O₃ microflake-based device was transformed from a gate voltage depletion mode to an oxygen depletion mode by FIB etching. The developed device exhibited excellent solar-blind PD performance with extremely high responsivity (1.8 × 10⁵ at 10 V), detectivity (3.4 × 10¹⁸ Jones at 10 V), and light-to-dark ratio (9.3 × 10⁸ at 5 V) as well as good repeatability and excellent stability. The intrinsic mechanism responsible for this performance was then systematically discussed. This work opens up a new avenue for the fabrication of high-performance β-Ga₂O₃-based low-dimensional PDs with high reproducibility by employing the FIB etching process.

High-Performance Solar-Blind UV Phototransistors Based on ZnO/Ga2O3 Heterojunction Channels

High-performance phototransistor-based solar-blind (200-280 nm) ultraviolet (UV) photodetectors (PDs) are constructed with a low-cost thin-film ZnO/Ga₂O₃ heterojunction. The optimized PD shows high spectral selectivity (R254/R365 > 1 × 10³) with a photo-to-dark current ratio of ∼10⁴, a responsivity of 113 mA/W, a detectivity of 1.25 × 10¹² Jones, and a response speed of 41 ms under 254 nm UV light irradiation. It is found that the gate electrode of a three-terminal phototransistor can amplify the responsivity and increase the photo-to-dark current ratio because of the different densities of field-induced electrons at different gate biases. In addition, the built-in electric field at the ZnO/Ga₂O₃ heterojunction interface can control the distribution of the photoinduced electrons and the total conductivity of the heterojunction, which can further enhance device performance. Together with the simple fabrication process, the achieved results suggest that the three-terminal ZnO/Ga₂O₃ heterojunction phototransistor is a promising candidate for highly sensitive solar-blind PDs.

High Performance of Zero-Power-Consumption MOCVD-Grown β-Ga2O3-Based Solar-Blind Photodetectors with Ultralow Dark Current and High-Temperature Functionalities

In this article, we report on high-performance deep ultraviolet photodetectors (DUV PDs) fabricated on metal-organic chemical vapor deposition (MOCVD)-grown β-Ga₂O₃ heteroepitaxy that exhibit stable operation up to 125 °C. The fabricated DUV PDs exhibit self-powered behavior with an ultralow dark current of 1.75 fA and a very high photo-to-dark-current ratio (PDCR) of the order of 10⁵ at zero bias and >10⁵ at higher biases of 5 and 10 V, which remains almost constant up to 125 °C. The high responsivity of 6.62 A/W is obtained at 10 V at room temperature (RT) under the weak illumination of 42.86 μW/cm² of 260 nm wavelength. The detector shows very low noise equivalent power (NEP) of 5.74 × 10^-14 and 1.03 × 10^-16 W/Hz^1/2 and ultrahigh detectivity of 5.51 × 10¹¹ and 3.10 × 10¹⁴ Jones at 0 and 5 V, respectively, which shows its high detection sensitivity. The RT UV-visible (260:500 nm) rejection ratios of the order of 10³ at zero bias and 10⁵ at 5 V are obtained. These results demonstrate the potential of Ga₂O₃-based DUV PDs for solar-blind detection applications that require high-temperature robustness.

Transferable Ga2O3 Membrane for Vertical and Flexible Electronics via One-Step Exfoliation

Transferable Ga₂O₃ thin film membrane is desirable for vertical and flexible solar-blind photonics and high-power electronics applications. However, Ga₂O₃ epitaxially grown on rigid substrates such as sapphire, Si, and SiC hinders its exfoliation due to the strong covalent bond between Ga₂O₃ and substrates, determining its lateral device configuration and also hardly reaching the ever-increasing demand for wearable and foldable applications. Mica substrate, which has an atomic-level flat surface and high-temperature tolerance, could be a good candidate for the van der Waals (vdW) epitaxy of crystalline Ga₂O₃ membrane. Beyond that, benefiting from the weak vdW bond between Ga₂O₃ and mica substrate, in this work, the Ga₂O₃ membrane is exfoliated and transferred to arbitrary flexible and adhesive tape, allowing for the vertical and flexible electronic configuration. This straightforward exfoliation method is verified to be consistent and reproducible by the transfer and characterization of thick (∼380 nm)/thin (∼95 nm) κ-phase Ga₂O₃ and conductive n-type β-Ga₂O₃. Vertical photodetectors are fabricated based on the exfoliated Ga₂O₃ membrane, denoting the peak response at ∼250 nm. Through the integration of Ti/Au Ohmic contact and Ni/Ag Schottky contact electrode, the vertical photodetector exhibits self-powered photodetection behavior with a responsivity of 17 mA/W under zero bias. The vdW-bond-assisted exfoliation of the Ga₂O₃ membrane demonstrated here could provide enormous opportunities in the pursuit of vertical and flexible Ga₂O₃ electronics.

Ultrasensitive Flexible κ-Phase Ga2O3 Solar-Blind Photodetector

Flexible Ga₂O₃ photodetectors have attracted considerable interest owing to their potential use in the development of implantable, foldable, and wearable optoelectronics. In particular, β-phase Ga₂O₃ has been most widely investigated due to the highest thermodynamic stability. However, high-quality β-phase Ga₂O₃ relies on the ultrahigh crystallization temperature (usually ≥750 °C), beyond the thermal tolerance of most flexible substrates. In this work, we epitaxially grow a high-quality metastable κ-phase Ga₂O₃ (002) thin film on a flexible mica (001) substrate under 680 °C and develop a flexible κ-Ga₂O₃ thin film photodetector with ultrahigh performance. Epitaxial κ-Ga₂O₃ and the mica substrate are maintained to be thermally stable up to 750 °C, suggesting their potential for harsh environment applications. The responsivity, on/off ratio, detectivity, and external quantum efficiency of the fabricated photodetector are 703 A/W, 1.66 × 10⁷, 4.08 × 10¹⁴ Jones, and 3.49 × 10⁵ %, respectively, for 250 nm incident light and a 20 V bias voltage. These values are record-high values reported to date for flexible Ga₂O₃ photodetectors. Furthermore, the flexible photodetector shows robust flexibility for bending radii of 1, 2, and 3 cm. More importantly, it shows strong mechanical stability against 10,000 bending test cycles. These results reveal the significance of high-quality κ-phase Ga₂O₃ grown heteroepitaxially on a flexible mica substrate, especially its potential for use in future flexible solar-blind detection systems.

Localized surface plasmon resonance-enhanced solar-blind Al0.4Ga0.6N MSM photodetectors exhibiting high-temperature robustness

The appealing properties of tunable direct wide bandgap, high-temperature robustness and chemical hardness, make Al_xGa_1-xN a promising candidate for fabricating robust solar-blind photodetectors (PDs). In this work, we have utilized the optical phenomenon of localized surface plasmon resonance (LSPR) in metal nanoparticles (NPs) to significantly enhance the performance of solar-blind Al_0.4Ga_0.6N metal-semiconductor-metal PDs that exhibit high-temperature robustness. We demonstrate that the presence of palladium (Pd) NPs leads to a remarkable enhancement by nearly 600, 300, and 462%, respectively, in the photo-to-dark current ratio (PDCR), responsivity, and specific detectivity of the Al_0.4Ga_0.6N PD at the wavelength of 280 nm. Using the optical power density of only 32μW cm^-2at -10 V, maximum values of ∼3 × 10³, 2.7 AW^-1, and 2.4 × 10¹³Jones are found for the PDCR, responsivity and specific detectivity, respectively. The experimental observations are supported by finite difference time domain simulations, which clearly indicate the presence of LSPR in Pd NPs decorated on the surface of Al_0.4Ga_0.6N. The mechanism behind the enhancement is investigated in detail, and is ascribed to the LSPR induced effects, namely, improved optical absorption, enhanced local electric field and LSPR sensitization effect. Moreover, the PD exhibits a stable operation up to 400 K, thereby exhibiting the high-temperature robustness desirable for commercial applications.

Synthesis of High-Quality Multilayer Hexagonal Boron Nitride Films on Au Foils for Ultrahigh Rejection Ratio Solar-Blind Photodetection

Solar-blind photodetectors have widespread applications due to the unique merit of a "black background" on the earth. However, most solar-blind photodetectors reported previously exhibited quite low rejection ratios (R_200nm/R_280nm < 10³) and were interfered with by light longer than 280 nm. Herein, by an ambient pressure chemical vapor deposition (CVD) method, large-area, clean, and uniform two-dimensional (2D) multilayer h-BN films with different thicknesses have been successfully synthesized on Au foils. The synthesized multilayer h-BN film is transparent to light longer than 280 nm, showing excellent optical and optoelectronic properties to weak solar-blind light (μW/cm²). This sensitive solar-blind h-BN photodetector exhibits ultrahigh rejection ratios (R_220nm/R_280nm > 10³ and R_220nm/R_290nm > 10⁴), a low dark current (10² fA), and a large detectivity (3.9 × 10¹⁰ Jones). It is noteworthy that the rejection ratio (R_220nm/R_290nm) here is superior to most of those previously reported based on traditional semiconductors. This large-scale, clean, and uniform multilayer h-BN film will contribute to the progress of next-generation optoelectronic devices.

Fast Response Solar-Blind Photodetector with a Quasi-Zener Tunneling Effect Based on Amorphous In-Doped Ga2O3 Thin Films

A high-performance solar-blind photodetector with a metal–semiconductor–metal structure was fabricated based on amorphous In-doped Ga₂O₃ thin films prepared at room temperature by radio frequency magnetron sputtering. The photodetector shows a high responsivity (18.06 A/W) at 235 nm with a fast rise time (4.9 μs) and a rapid decay time (230 μs). The detection range was broadened compared with an individual Ga₂O₃ photodetector because of In doping. In addition, the uneven In distribution at different areas in the film results in different resistances, which causes a quasi-Zener tunneling internal gain mechanism. The quasi-Zener tunneling internal gain mechanism has a positive impact on the fast response speed and high responsivity.

Solar-Blind Photodetector with High Avalanche Gains and Bias-Tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures

The metastable α-phase Ga₂O₃ is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga₂O₃ remains challenging. To this end, single crystalline α-Ga₂O₃ epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-Ga₂O₃/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 10³ and a detectivity of 9.66 × 10¹² cm Hz^1/2 W^-1. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W^-1 at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga₂O₃ and Ga₂O₃/ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 10³ and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 10⁵ and a high responsivity of 1.10 × 10⁴ A W^-1. Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.

Self-Powered Solar-Blind Photodetector with Fast Response Based on Au/β-Ga2O3 Nanowires Array Film Schottky Junction

Because of the direct band gap of 4.9 eV, β-Ga2O3 has been considered as an ideal material for solar-blind photodetection without any bandgap tuning. Practical applications of the photodetectors require fast response speed, high signal-to-noise ratio, low energy consumption and low fabrication cost. Unfortunately, most reported β-Ga2O3-based photodetectors usually possess a relatively long response time. In addition, the β-Ga2O3 photodetectors based on bulk, the individual 1D nanostructure, and the film often suffer from the high cost, the low repeatability, and the relatively large dark current, respectively. In this paper, a Au/β-Ga2O3 nanowires array film vertical Schottky photodiode is successfully fabricated by a simple thermal partial oxidation process. The device exhibits a very low dark current of 10 pA at -30 V with a sharp cutoff at 270 nm. More interestingly, the 90-10% decay time of our device is only around 64 μs, which is much quicker than any other previously reported β-Ga2O3-based photodetectors. Besides, the self-powering, the excellent stability and the good reproducibility of Au/β-Ga2O3 nanowires array film photodetector are helpful to its commercialization and practical applications.