Enhancement of solar blind full band absorption in photodetector with Ga2O3 nanopore and Al nanograting.

In this paper, we presented a novel double-layer light-trapping structure consisting of nanopores and nanograting positioned on both the surface and bottom of a gallium oxide-based solar-blind photodetector. Utilizing the finite element method (FEM), we thoroughly investigated the light absorption enhancement capabilities of this innovative design. The simulation results show that the double-layer nanostructure effectively combines the light absorption advantages of nanopores and nanogratings. Compared with thin film devices and devices with only nanopore or nanograting structures, double-layer nanostructured devices have a higher light absorption, achieving high light absorption in the solar blind area.

Structures, influences, and formation mechanism of planar defects on (100), (001) and (-201) planes in ß-Ga2O3 crystals.

The ß-Ga2O3 crystal is a significant ultrawide bandgap semiconductor with great potential in ultraviolet optoelectronics and high-power devices. Planar defects in ß-Ga2O3 have been observed in experiments, but their structures, influences, formation mechanism, and controlling methods remain to be studied. We conducted a comprehensive study of ß-Ga2O3 planar defects using density functional theory. We determined the atomic structures of planar defects (stacking faults and twins) on (100), (001), and (-201) planes in ß-Ga2O3 crystals and calculated the formation energy and band structure of each defect. Our results indicate that the formation energy of stacking faults on the (100) plane and twins on the (100) and (-201) planes was extremely low, which explained why these planar defects were observed readily. We also studied the influence of common impurities (Si, Sn, Al, H) and vacancies in ß-Ga2O3 crystals on the formation of these planar defects. Our findings revealed that specific impurities and vacancies could facilitate the formation of planar defects or even make them spontaneous. This research provides critical insights into the atomic structures of planar defects in ß-Ga2O3, and explains why they form readily from the perspective of formation energy. These insights are important for future research into ß-Ga2O3 defects.

Passively Q-switched single crystal fiber pulsed laser at 1.05†µm with T3C2Tx as the saturable absorber.

In this paper, Ti3C2Tx MXene prepared by LiF/HCl etching method was spin-coated on glass substrate and sapphire substrate as the saturable absorber (SA), and the MXene SA is combined with Yb: LuAG single crystal fiber (SCF) for the first time to achieve a 1.05 µm passively Q-switched pulsed laser output with the average power, pulse width, and repetition frequency of 1.989 W, 149.6 ns, and 365.44 kHz, respectively, which is the highest average power ever reported for passively Q-switched SCF pulsed lasers. This work enriches the research on SCF pulsed lasers and provides a feasible approach for achieving high-power all-solid-state pulsed lasers.

Formation of Au, Pt, and bimetallic Au-Pt nanostructures from thermal dewetting of single-layer or bilayer thin films.

Formation of Au, Pt, and bimetallic Au-Pt nanostructures by thermal dewetting of single-layer Au, Pt and bilayer Au-Pt thin films on Si substrates was systematically studied. The solid-state dewetting of both single-layer and bilayer metallic films was shown to go through heterogeneous void initiation followed by void growth via capillary agglomeration. For the single-layer of Au and Pt films, the void growth started at a temperature right above the Hüttig temperature, at which the atoms at the surface or at defects become mobile. Uniformly distributed Au (7 ± 1 nm to 33 ± 8 nm) and Pt (7 ± 1 nm) NPs with monodispersed size distributions were produced from complete dewetting achieved for thinner 1.7-5.5 nm thick Au and 1.4 nm thick Pt films, respectively. The NP size is strongly dependent on the initial thin film thickness, but less so on temperature and time. Thermal dewetting of Au-Pt bilayer films resulted in partial dewetting only, forming isolated nano-islands or large particles, regardless of sputtering order and total thin film thickness. The increased resistance to thermal dewetting shown in the Au-Pt bilayer films as compared to the individual Au or Pt layer is a reflection of the stabilizing effect that occurs upon adding Pt to Au in the bimetallic system. Energy dispersive x-ray spectroscopic analysis showed that the two metals in the bilayer films broke up together instead of dewetting individually. According to the x-ray diffraction analysis, the produced Au-Pt nanostructures are phase-segregated, consisting of an Au-rich phase and a Pt-rich phase.

Improvement of Swanepoel method for deriving the thickness and the optical properties of chalcogenide thin films.

A tangencypoint method (TPM) is presented to derive the thickness and optical constants of chalcogenide thin films from their transmission spectra. It solves the problem of the abnormal value of thickness in the strong absorption region obtained by Swanepoel method. The accuracy of the thickness and refractive index is better than 0.5% by using this method. Moreover, comparing with Swanepoel method by using the same simulation and experimental data from the transmission spectrum, the accuracy of the thickness and refractive index obtained by the TPM is higher in the strong absorption region. Finally the dispersion and absorption coefficient of the chalcogenide films are obtained based on the experimental data of the transmission spectrum by using the TPM.

Femtosecond solid-state laser based on a few-layered black phosphorus saturable absorber.

In this Letter, a high-quality, few-layered black phosphorus (BP) saturable absorber (SA) was fabricated successfully, and a femtosecond solid-state laser modulated by BP-SA was experimentally demonstrated for the first time, to the best of our knowledge. Pulses as short as 272 fs were achieved with an average output power of 0.82 W, corresponding to the pulse energy of 6.48 nJ and peak power of 23.8 MW. So far, these represent the shortest pulse duration and highest output power ever obtained with a BP-based mode-locked solid-state laser. The results indicate the promising potential of few-layered BP-SA for applications in solid-state femtosecond mode-locked lasers.

High-power passively mode-locked laser at 1062.4 nm based on Nd:LaGGG disordered crystal.

A diode-pumped passively continuous-wave mode-locked Nd:(La(x)Gd(1-x))3Ga5O12 (Nd:LaGGG) laser at 1062.4 nm with a semiconductor saturable absorber mirror was demonstrated for the first time, to the best of our knowledge. Pulses with duration of 12.78 ps were produced at a repetition rate of 59.8 MHz. A maximum average mode-locked output power of 3.18 W was obtained at the absorbed pumped power of 10.12 W, corresponding to a slope efficiency of 35.7% and a peak power of 4.2 kW. As far as we know, this is the highest power obtained in the passively mode-locking operation with Nd3+-doped disordered garnet crystals.

Linear and nonlinear optical properties of terbium calcium oxyborate single crystals.

The linear and nonlinear optical properties of TbCa4O(BO3)3 (abbreviated as TbCOB) single crystals were investigated for the first time. The refractive indices of TbCOB at several wavelengths were measured by using the minimum deviation method and the parameters of Sellmeier's dispersion equation were determined from the experimental data. The complete set of six second-order nonlinear optical (NLO) coefficients of TbCOB single crystals were obtained using the Maker fringe (FM) technique, with the largest d32 being on the order of 1.65 pm/V. Moreover, the phase-matching (PM) configurations of second-order harmonic generation (SHG) in the principal planes were calculated, and the largest effective NLO coefficient is deff = 0.86 pm/V along (22.56°, 180°) PM direction. The SHG conversion efficiency from 1064 nm to 532 nm of 8 mm long crystal samples without AR coating along this direction was achieved 57.1% at 28.2 mW input power, and it has a small walk-off angle of 13.8 mrad. In addition, the comparison and discussion with GdCOB and YCOB were carried out.

Growth, Spectroscopy, and Laser Performance of a 2.79 µm Er: YSGG Single Crystal Fibers.

Single crystal fibers combine the great specific surface area of fibers and the single crystal property of the bulk crystal which shows great potential for a high-power laser. For an Er-doped crystal, due to the fluorescence quenching at the 3 µm wavelength, high Er doping is necessary to increase the fluorescent up-conversion for the breaking limitation. However, a high Er doping concentration must lead to high heat accumulation, resulting in poor laser performance. Compared with an Er-doped bulk crystal, Er-doped SCF has the great potential to remove the heat in the crystal, and it is easy to obtain a high power. In this paper, Er: Y3Sc2Ga3O12 (Er: YSGG) single crystals were successfully grown using the micro-pulling-down method (µ-PD). Owing to the stably grown interface, the diameter of the crystal is 2 mm with a length up to 80 mm. Then, the measurements of Laue spots and Er3+ distribution indicated that our crystals have a high quality. Based on the as-prepared Er: YSGG SCF, the continuous-wave (CW) laser operations at 2794 nm were realized. The maximum output was 166 mW with a slope efficiency of up to 10.99%. These results show that Er: YSGG SCF is a suitable material for future high-power 3 µm laser operation.

Toward Smart, Flexible, and Omnidirectional Self-Powered Photodetection by an All-Solution-Processed In2O3/Pbl2 Heterojunction.

Amorphous In2O3 film is emerging as a promising oxide semiconductor for next-generation electronics and optoelectronics owing to high mobility and wide band gap. However, the persistent photocurrent phenomenon and high carrier concentration in amorphous In2O3 film are challenging the photodetection performances, resulting in a long response time and low Ilight/Idark ratio. In this work, the In2O3/PbI2 heterojunction is constructed by an all-solution synthesis process to inhibit the persistent photocurrent phenomenon and large dark current. Benefiting from the built-in electric field at the heterojunction interface, the In2O3/PbI2 heterojunction photodetector exhibits excellent self-powered photodetection performances with an ultralow dark current of 10-12 A, a high Ilight/Idark ratio of 104, and fast response times of 0.6/0.6 ms. Furthermore, the entire solution synthesis process and amorphous characteristics enable the fabrication of an In2O3/PbI2 heterojunction photodetector on arbitrary substrates to realize specific functions. When configured onto the polyimide substrate, the In2O3/PbI2 heterojunction photodetector shows excellent mechanical flexibility, bending endurance, and photoresponse stability. When implanted onto the transparent substrate, the In2O3/PbI2 heterojunction photodetector exhibits an outstanding omnidirectional self-powdered photodetection performance and imaging capability. All results pave the way for an all-solution-processed amorphous In2O3 film in advanced high-performance photodetectors.

High-efficiency femtosecond Yb:Gd3Al(0.5)Ga(4.5)O12 mode-locked laser based on reduced graphene oxide.

A diode-pumped Yb-doped Gd(3)Al(0.5)Ga(4.5)O(12) mode-locked bulk laser based on chemically reduced graphene oxide (RGO) has been demonstrated for the first time to our best knowledge. Pulses with duration of 643 fs were produced at the central wavelength of 1041.1 nm. A maximum average output power of 0.8 W was obtained from the RGO mode-locked laser, corresponding to a slope efficiency of 20.1% and a peak power of 27.6 kW. The results indicate that RGO is suitable for obtaining high-power and high-efficiency ultrafast lasers.

Squeeze-Printing Ultrathin 2D Gallium Oxide out of Liquid Metal for Forming-Free Neuromorphic Memristors.

Two-dimensional (2D) metal oxides exhibit extraordinary mechanical and electronic properties, leading to new paradigms in the design of electronic and optical systems. However, as a representative, a 2D Ga2O3-based memristor has rarely been touched, which is hindered by challenges associated with large-scale material synthesis. In this work, the ultrathin 2D Ga2O3 layer (∼3 nm thick) formation on the liquid gallium (Ga) surface is transferred with lateral dimensions over several centimeters on a substrate via the squeeze-printing strategy. 2D Ga2O3-based memristors exhibit forming-free and bipolar switching behaviors, which also reveal essential functions of biological synapse, including paired-pulse facilitation, spiking timing-dependent plasticity, and long-term depression and potentiation. These results demonstrate the potential of 2D Ga2O3 material for neuromorphic computing and open up an avenue for future electronics application, such as deep UV photodetectors, multimode nanoresonators, and power switching devices.

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

In this work, square nanopore arrays were developed on the surface of ß-Ga2O3 microflakes using focused ion beam (FIB) etching, and solar-blind photodetectors (PDs) were fabricated based on the ß-Ga2O3 microflakes with square nanopore arrays. The ß-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 ß-Ga2O3-based low-dimensional PDs with high reproducibility by employing the FIB etching process.

Thermoluminescence Studies of Proton-Irradiated Cr-, Mg-Codoped ß-Ga2O3.

Chromium-doped Ga2O3, with intense Cr3+-related red-infrared light emission, is a promising semiconductor material for optical sensors. This work constitutes a comprehensive study of the thermoluminescence properties of Cr-, Mg-codoped ß-Ga2O3 single crystals, both prior to and after proton irradiation. The thermoluminescence investigation includes a thorough analysis of measurements with different ß- irradiation doses used to populate the trap levels, with preheating steps to disentangle overlapping peaks (TM-TSTOP and initial rise methods) and finally by computationally fitting to a theoretical expression. At least three traps with activation energies of 0.84, 1.0, and 1.1 eV were detected. By comparison with literature reports, they can be assigned to different defect complexes involving oxygen vacancies and/or common contaminants/dopants. Interestingly, the thermoluminescence signal is enhanced by the proton irradiation while the type of traps is maintained. Finally, the pristine glow curve was recovered on the irradiated samples after an annealing step at 923 K for 10 s. These results contribute to a better understanding of the defect levels in Cr-, Mg-codoped ß-Ga2O3 and show that electrons released from these traps lead to Cr3+-related light emission that can be exploited in dosimetry applications.

Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na2Cl3 and Na4Cl5 and Bromide Na4Br5.

The field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides), is rapidly evolving. Here, we present the synthesis of three sodium halides with unpredicted chemical compositions and structures (tP10-Na2Cl3, hP18-Na4Cl5, and hP18-Na4Br5), a series of isostructural cubic cP8-AX3 halides (NaCl3, KCl3, NaBr3, and KBr3), and a trigonal potassium chloride (hP24-KCl3). The high-pressure syntheses were realized at 41-80 GPa in diamond anvil cells laser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction (XRD) provided the first accurate structural data for the symmetric trichloride Cl3- anion in hP24-KCl3 and revealed the existence of two different types of infinite linear polyhalogen chains, [Cl]∞n- and [Br]∞n-, in the structures of cP8-AX3 compounds and in hP18-Na4Cl5 and hP18-Na4Br5. In Na4Cl5 and Na4Br5, we found unusually short, likely pressure-stabilized, contacts between sodium cations. Ab initio calculations support the analysis of structures, bonding, and properties of the studied halogenides.

Crystal Growth, Thermal and Spectral Properties of Er: LGGG Crystal.

A high-quality Er3+-doped (Gd1-xLux)3Ga5O12 (Er: LGGG) laser crystal with a size of Φ 36 × 45 mm3 was successfully grown by the Czochralski (Cz) method for the first time. The effective segregation coefficient of Er3+ was determined to be 0.97, close to 1, and, thus, the uniform high-quality Er: LGGG crystal can be grown. In addition, the thermal and spectroscopic properties of Er: LGGG were investigated. Based on the measured characteristics, the Er: LGGG crystal has a huge potential for use in the 3.0 µm mid-infrared laser because of its outstanding optical quality, extraordinary thermal conductivity and stable structure.

ß-Ga2O3 Nanostructures: Chemical Vapor Deposition Growth Using Thermally Dewetted Au Nanoparticles as Catalyst and Characterization.

ß-Ga2O3 nanostructures, including nanowires (NWs), nanosheets (NSHs), and nanorods (NRs), were synthesized using thermally dewetted Au nanoparticles as catalyst in a chemical vapor deposition process. The morphology of the as-grown ß-Ga2O3 nanostructures depends strongly on the growth temperature and time. Successful growth of ß-Ga2O3 NWs with lengths of 7-25 µm, NSHs, and NRs was achieved. It has been demonstrated that the vapor-liquid-solid mechanism governs the NW growth, and the vapor-solid mechanism occurs in the growth of NSHs and NRs. The X-ray diffraction analysis showed that the as-grown nanostructures were highly pure single-phase ß-Ga2O3. The bandgap of the ß-Ga2O3 nanostructures was determined to lie in the range of 4.68-4.74 eV. Characteristic Raman peaks were observed with a small blue and red shift, both of 1-3 cm-1, as compared with those from the bulk, indicating the presence of internal strain and defects in the as-grown ß-Ga2O3 nanostructures. Strong photoluminescence emission in the UV-blue spectral region was obtained in the ß-Ga2O3 nanostructures, regardless of their morphology. The UV (374-377 nm) emission is due to the intrinsic radiative recombination of self-trapped excitons present at the band edge. The strong blue (404-490 nm) emissions, consisting of five bands, are attributed to the presence of the complex defect states in the donor (VO) and acceptor (VGa or VGa-O). These ß-Ga2O3 nanostructures are expected to have potential applications in optoelectronic devices such as tunable UV-Vis photodetectors.

Flexible Omnidirectional Self-Powered Photodetectors Enabled by Solution-Processed Two-Dimensional Layered PbI2 Nanoplates.

Realizing omnidirectional self-powered photodetectors is central to advancing next-generation portable and smart photodetector systems. However, the traditional omnidirectional photodetector is typically achieved by integrating complex hemispherical microlens on multiple photodetectors, which makes the detection system cumbersome and restricts its application in the portable field. Here, facile and high-performance flexible omnidirectional self-powered photodetectors are achieved by solution-processed two-dimensional (2D) layered PbI2 nanoplates on transparent conducting substrates. Characterization of PbI2 nanoplates microstructural/compositional and their photodetection properties have been systematically characterized. Under the irradiation of a 405 nm laser, the photodetectors exhibit an impressively low dark current of 10-13 A, a high light on/off ratio up to 106, and a fast rise/decay response time of 2/3 ms. Importantly, when light irradiates the photodetector at 5°, it can still maintain high photodetection properties, realizing almost 360° omnidirectional self-powered photodetection. What is more, these self-powered photodetectors exhibit robust omnidirectional photoresponse stability of flexibility even after bending for 1200 cycles. Thus, this work broadens the applicability of 2D layered nanoplates for further extending its applications in advanced optoelectronic devices.

Synthesis of rare-earth metal compounds through enhanced reactivity of alkali halides at high pressures.

Chemical stability of the alkali halides NaCl and KCl has allowed for their use as inert media in high-pressure high-temperature experiments. Here we demonstrate the unexpected reactivity of the halides with metals (Y, Dy, and Re) and iron oxide (FeO) in a laser-heated diamond anvil cell, thus providing a synthetic route for halogen-containing binary and ternary compounds. So far unknown chlorides, Y2Cl and DyCl, and chloride carbides, Y2ClC and Dy2ClC, were synthesized at ~40 GPa and 2000 K and their structures were solved and refined using in situ single-crystal synchrotron X-ray diffraction. Also, FeCl2 with the HP-PdF2-type structure, previously reported at 108 GPa, was synthesized at ~160 GPa and 2100 K. The results of our ab initio calculations fully support experimental findings and reveal the electronic structure and chemical bonding in these compounds.

Continuous-wave and passively Q-switched laser performance of LD-end-pumped 1062 nm Nd:GAGG laser.

Continuous-wave (CW) and passively Q-switched operations of LD-end-pumped Nd:Gd(3)Al(x)Ga(5-x)O(12) (Nd:GAGG) laser at 1062 nm were reported. The highest CW output power of 5.7 W was obtained, corresponding to an optical conversion efficiency and slope efficiency of 51.0% and 54.5%, respectively. The CW output efficiency of Nd:GAGG laser is comparable and even better than that of Nd:GGG. The passively Q-switched output was realized for the first time to our knowledge. In addition, a maximum output power of 1.12 W, a maximum pulse repetition rate of 39 kHz and a minimum pulse width of 6 ns were obtained by using Cr(4+):YAG as the saturable absorber.