Development of solar-blind photodetectors based on Si-implanted β-Ga(2)O(3)

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.

High-Photoresponsivity Self-Powered a-, ε-, and β-Ga2O3/p-GaN Heterojunction UV Photodetectors with an In Situ GaON Layer by MOCVD

In this paper, self-powered ultraviolet (UV) photodetectors with high response performance based on Ga₂O₃/p-GaN were fabricated by metal-organic chemical vapor deposition (MOCVD). The effects of different crystal phases of Ga₂O₃ (including a, ε, ε/β, and β) grown on p-GaN films on the performance of photodetectors were systematically studied. Moreover, an in situ GaON dielectric layer improved the responsivity of Ga₂O₃/p-GaN photodetectors by 20 times. All Ga₂O₃/p-GaN photodetectors showed self-power capability without bias. An ultralow dark current of 3.08 pA and a I_photo/I_dark ratio of 4.1 × 10³ (1.8 × 10³) under 254 nm (365 nm) light were obtained for the β-Ga₂O₃/p-GaN photodetector at 0 V bias. Furthermore, the β-Ga₂O₃/p-GaN photodetector showed excellent sensitivity with a high responsivity of 3.8 A/W (0.83 A/W), a fast response speed of 66/36 ms (36/73 ms), and a high detectivity of 1.12 × 10¹⁴ Jones (2.44 × 10¹³ Jones) under 254 nm (365 nm) light at 0 V bias. The carrier transport mechanism of the Ga₂O₃/p-GaN self-powered photodetector was also analyzed through the device energy band diagram. This work provides critical information for the design and fabrication of high-performance self-powered Ga₂O₃/p-GaN UV photodetectors, opening the door to a variety of photonic systems and applications without an external power supply.

Predicting the Raman spectra of ferroelectric phases in two-dimensional Ga2O3 monolayer

We investigate the vibrational properties and Raman spectra of the two-dimensional Ga₂O₃ monolayer, using density functional theory. Two ferroelectric (FE) phases of the Ga₂O₃ monolayer with wurtzite (WZ) and zinc blende (ZB) structures (FE-WZ and FE-ZB, respectively) are considered. The Raman tensor and angle-dependent Raman intensities of two major Raman peaks (A11 and A21) in both FE-WZ (497, and 779 cm^-1) and FE-ZB (481, and 772 cm^-1) Ga₂O₃ monolayers, are calculated for the polarization of scattered light, parallel and perpendicular to that of the incident light. The characteristics of angle-dependent Raman intensities are analyzed. The average non-resonant Raman spectra of the minor peaks in FE-WZ (E¹) and FE-BZ (E¹ and E²) are compared with those of major peaks A11 and A21. These predictions of the Raman spectra of the Ga₂O₃ monolayer may guide the rational design of two-dimensional optical devices.

Hybrid metal/Ga2O3/GaN ultraviolet detector for obtaining low dark current and high responsivity

In this work, we have proposed and fabricated a metal/Ga₂O₃/GaN hybrid structure metal-semiconductor-metal ultraviolet photodetector with low dark current and high responsivity. The Schottky contact of Ni/Ga₂O₃ makes the Ga₂O₃ layer fully depleted. The strong electric field in the Ga₂O₃ depletion region can push the photo-induced electrons from the Ga₂O₃ layer into the GaN layer for more efficient carrier transport. Therefore, the hybrid structure simultaneously utilizes the advantage of the absorption to solar-blind ultraviolet light by the Ga₂O₃ layer and the high electron mobility of the GaN layer. Thus, the dark current and the photocurrent for the proposed device can be greatly improved. As a result, an extremely high photo-to-dark-current ratio of 1.46 × 10⁶ can be achieved. Furthermore, quick rise and fall times of 0.213 s and 0.027 s at the applied bias of 6 V are also obtained, respectively.

Silicon: quantum dot photovoltage triodes

Silicon is widespread in modern electronics, but its electronic bandgap prevents the detection of infrared radiation at wavelengths above 1,100 nanometers, which limits its applications in multiple fields such as night vision, health monitoring and space navigation systems. It is therefore of interest to integrate silicon with infrared-sensitive materials to broaden its detection wavelength. Here we demonstrate a photovoltage triode that can use silicon as the emitter but is also sensitive to infrared spectra owing to the heterointegrated quantum dot light absorber. The photovoltage generated at the quantum dot base region, attracting holes from silicon, leads to high responsivity (exceeding 410 A·W-1 with Vbias of -1.5 V), and a widely self-tunable spectral response. Our device has the maximal specific detectivity (4.73 × 1013 Jones with Vbias of -0.4 V) at 1,550 nm among the infrared sensitized silicon detectors, which opens a new path towards infrared and visible imaging in one chip with silicon technology compatibility.

Highly sensitive X-ray detector based on a β-Ga2O3:Fe single crystal

β-Ga₂O₃ semiconductor crystal is of wide band gap and high radiation resistance, which shows great potential for applications such as medical imaging, radiation detections, and nuclear physical experiments. However, developing β-Ga₂O₃-based X-ray radiation detectors with high sensitivity, fast response speed, and excellent stability remains a challenge. Here we demonstrate a high-performance X-ray detector based on a Fe doped β-Ga₂O₃ (β-Ga₂O₃:Fe) crystal grown by the float-zone growth method, which consists of two vertical Ti/Au electrodes and a β-Ga₂O₃:Fe crystal with high resistivity. The resistivity of the β-Ga₂O₃:Fe crystal exceeds 10¹² Ω cm owed to the compensation of the Fe ions and the free electrons. The detector shows short response time (0.2 s), high sensitivity (75.3 µC Gy_air ^-1 cm^-2), and high signal-to-noise ratio (100), indicating great potential for X-ray radiation detection.

Non-steady-state photo-EMF in β-Ga2O3 crystals at λ = 457 nm

The non-steady-state photoelectromotive force is excited in a monoclinic gallium oxide crystal at wavelength λ = 457 nm. The crystal grown in an oxygen atmosphere is insulating and highly transparent for a visible light, nevertheless, the formation of dynamic space-charge gratings and observation of the photo-EMF signal is achieved without application of any electric field to the sample. The dependencies of the signal amplitude on the frequency of phase modulation, light intensity, spatial frequency and light polarization are measured. The material demonstrates the anisotropy along the [100] and [010] directions, namely, there is a small difference in the transport parameters and a pronounced polarization dependence of the signal. The crystal's photoconductivity, responsivity and diffusion length of electrons are estimated for the chosen light wavelength and compared with the ones for other wide-bandgap crystals.

Tunable Optical Properties of Amorphous-Like Ga2O3 Thin Films Deposited by Electron-Beam Evaporation with Varying Oxygen Partial Pressures

Ga₂O₃ thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10⁻² Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the Ga₂O₃ films was analyzed using sophisticated techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet-visible spectroscopy and a laser-induced damage test system. The correlation between the oxygen partial pressure and the film’s properties in optics and materials were investigated. XRD and Raman revealed that all films were amorphous in spite of applying a varying oxygen partial pressure. With the change of oxygen partial pressure, XPS data indicated that the content of oxygen in the Ga₂O₃ films could be broadly modulable. As a result, a changeable refractive index of the Ga₂O₃ film is realizable and a variable blue-shift of absorption edges in transmittance spectra of the films is achievable. Moreover, the damage threshold value varied from 0.41 to 7.51 J/cm² according to the rise of oxygen partial pressure. These results demonstrated that the optical properties of Ga₂O₃ film can be broadly tunable by controlling the oxygen content in the film.

The Investigation of Hybrid PEDOT:PSS/β-Ga2O3 Deep Ultraviolet Schottky Barrier Photodetectors

In this paper, the hybrid β-Ga₂O₃ Schottky diodes were fabricated with PEDOT:PSS as the anode. The electrical characteristics were investigated when the temperature changes from 298 K to 423 K. The barrier height ϕ_b increases, and the ideality factor n decreases as the temperature increases, indicating the presence of barrier height inhomogeneity between the polymer and β-Ga₂O₃ interface. The mean barrier height and the standard deviation are 1.57 eV and 0.212 eV, respectively, after taking the Gaussian barrier height distribution model into account. Moreover, a relatively fast response speed of less than 320 ms, high reponsivity of 0.6 A/W, and rejection ratio of R_{254 nm}/R_{400 nm} up to 1.26 × 10³ are obtained, suggesting that the hybrid PEDOT:PSS/β-Ga₂O₃ Schottky barrier diodes can be used as deep ultraviolet (DUV) optical switches or photodetectors.

The enhancement mechanism of photo-response depending on oxygen pressure for Ga2O3 photo detectors

We have optimized the responsivity and response speed of a β-Ga₂O₃-based photodetector. The β-Ga₂O₃ thin films were deposited on a glass substrate under various oxygen partial pressures from 0 to 50 mTorr using pulsed laser deposition. Time-response measurements show that the as-grown β-Ga₂O₃ at an oxygen partial pressure of 50 mTorr has the fastest response speed and decay times of 33 and 100 ms, which are better than those prepared at lower oxygen pressures. This sample also showed a high photoresponsivity of 5 A W^-1 and detectivity of 10¹² cmHz^1/2/W. The high performance of the β-Ga₂O₃ detector grown at the oxygen partial pressure of 50 mTorr might be due to the reduction of oxygen vacancies caused by the increase in oxygen content during deposition. The results reveal the importance of the oxygen processing gas in promoting photodetector performance.

High-performance β-Ga2O3 thickness dependent solar blind photodetector

Gallium oxide (Ga₂O₃) has been studied as one of the most promising wide bandgap semiconductors during the past decade. Here, we prepared high quality β-Ga₂O₃ films by pulsed laser deposition. β-Ga₂O₃ films of different thicknesses were achieved and their crystal properties were comprehensively studied. As thickness increases, grain size and surface roughness are both increased. Based on these β-Ga₂O₃ films, a series of ultraviolet (UV) photodetectors with interdigital electrodes structure were prepared. These devices embrace an ultralow dark current of 100 fA, and high photocurrent on/off ratio of 10E8 under UV light illumination. The photoresponse time is 4 ms which is faster than most of previous works. This work paves the way for the potential application of Ga₂O₃ in the field of UV detection.

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.

Diamond based photodetectors for solar-blind communication

High performance solar-blind photodetectors have been fabricated from diamond wafers. The peak responsivity is 13.0 A/W at 222 nm with a dark current of 0.93 nA under 60 V bias. The rise and decay times of the photodetector are about 1.3 µs and 203 µs, respectively. The responsivity and response time of the device are both among the best values ever reported for diamond-based photodetectors. A solar-blind optical communication system has been constructed by employing the diamond photodetector as a signal receiver for the first time. Benefiting from the high spectral selectivity of the diamond photodetector, the communication system has excellent anti-interference ability. The results reported in this paper may pave the way for the future application of diamond-based solar-blind photodetectors in confidential communications.

A Review of Recent Applications of Ion Beam Techniques on Nanomaterial Surface Modification: Design of Nanostructures and Energy Harvesting

Nanomaterials have gained plenty of research interest because of their excellent performance, which is derived from their small size and special structure. In practical applications, to acquire nanomaterials with high performance, many methods have been used to modulate the structure and components of materials. To date, ion beam techniques have extensively been applied for modulating the performance of various nanomaterials. Energetic ion beams can modulate the surface morphology and chemical components of nanomaterials. In addition, ion beam techniques have also been used to fabricate nanomaterials, including 2D materials, nanoparticles, and nanowires. Compared with conventional methods, ion beam techniques, including ion implantation, ion irradiation, and focused ion beam, are all pure physical processes; these processes do not introduce any impurities into the target materials. In addition, ion beam techniques exhibit high controllability and repeatability. Here, recent progress in ion beam techniques for nanomaterial surface modification is systematically summarized and existing challenges and potential solutions are presented.

Zero-biased deep ultraviolet photodetectors based on graphene/cleaved (100) Ga2O3 heterojunction

In this paper, fast response, zero-biased, solar-blind UV photodetectors based on graphene/β-Ga₂O₃ heterojunctions were fabricated by transferring a monolayer graphene onto fresh cleaved β-Ga₂O₃ (100) single crystal substrate. At zero bias, the photo responsivity at 254 nm and the UV/visible rejection ratio (R₂₃₅ nm/R₄₀₀ nm) and the response time are obtained to be 10.3 mA/W and 2.28 × 10² and 2.24 μs, respectively, for the graphene/β-Ga₂O₃ (100) detector. The fast response and the high sensitivity can be attributed to the high mobility and UV transparency of graphene top-electrode and the low defect density of the β-Ga₂O₃ (100) cleaved surface. Such zero-biased detectors are very promising for next-generation solar-blind UV photodetection.

Graphene Interdigital Electrodes for Improving Sensitivity in a Ga2O3:Zn Deep-Ultraviolet Photoconductive Detector

Graphene (Gr) has been widely used as a transparent electrode material for photodetectors because of its high conductivity and high transmittance in recent years. However, the current low-efficiency manipulation of Gr has hindered the arraying and practical use of such detectors. We invented a multistep method of accurately tailoring graphene into interdigital electrodes for fabricating a sensitive, stable deep-ultraviolet photodetector based on Zn-doped Ga₂O₃ films. The fabricated photodetector exhibits a series of excellent performance, including extremely low dark current (∼10^-11 A), an ultrahigh photo-to-dark ratio (>10⁵), satisfactory responsivity (1.05 A/W), and excellent selectivity for the deep-ultraviolet band, compared to those with ordinary metal electrodes. The raise of photocurrent and responsivity is attributed to the increase of incident photons through Gr and separated carriers caused by the built-in electric field formed at the interface of Gr and Ga₂O₃:Zn films. The proposed ideas and methods of tailoring Gr can not only improve the performance of devices but more importantly contribute to the practical development of graphene.

Recent Advances in β-Ga2O3-Metal Contacts

Ultra-wide bandgap beta-gallium oxide (β-Ga₂O₃) has been attracting considerable attention as a promising semiconductor material for next-generation power electronics. It possesses excellent material properties such as a wide bandgap of 4.6-4.9 eV, a high breakdown electric field of 8 MV/cm, and exceptional Baliga's figure of merit (BFOM), along with superior chemical and thermal stability. These features suggest its great potential for future applications in power and optoelectronic devices. However, the critical issue of contacts between metal and Ga₂O₃ limits the performance of β-Ga₂O₃ devices. In this work, we have reviewed the advances on contacts of β-Ga₂O₃ MOSFETs. For improving contact properties, four main approaches are summarized and analyzed in details, including pre-treatment, post-treatment, multilayer metal electrode, and introducing an interlayer. By comparison, the latter two methods are being studied intensively and more favorable than the pre-treatment which would inevitably generate uncontrollable damages. Finally, conclusions and future perspectives for improving Ohmic contacts further are presented.