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The twin boundary (TB) is a planar defect that both destroys the integrity of the crystal and significantly deteriorates the performance of semiconductor devices. However, limited research exists on the initial crystal nucleus kinetics of TB, which is a crucial aspect for a comprehensively understanding the twinning mechanism. Here, the nucleation kinetics process of TB has been thoroughly studied regarding crystal morphology, growth interface at the atomic scale, and first-principle calculations in β-Ga2O3. The nucleation kinetics process of TB originates from the smooth interface growth mode of (100)-B, which requires a significant degree of supercooling. During the crystal growth, the large degree of supercooling in front of the (100)-B plane at the three-phase boundary (TPB) leads to nucleation of TB. The twin type of β-Ga2O3 is recognized as twin-B among the two thermodynamically equivalent structures. It is a glide reflection twin whose glide process initiates with a 1/4 length of the [001] vector and then with a 1/2 length of the [010] vector. This study has developed the nucleation kinetics of TB, thus enriching the theory of crystal defects. The revealed relationship between TB and the smooth interface growth mode holds great significance for guiding the suppression of twins.

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.

The chemical stability of alkali halides has caused them to be exploited as inert media in high-pressure, high-temperature experiments. Here, NaCl and KCl are unexpectedly found to react with yttrium, dysprosium and iron oxide in a laser-heated diamond anvil cell, producing Y2Cl, DyCl, Y2ClC and Dy2ClC at ~40 GPa and 2000 K and FeCl2 at ~160 GPa and 2100 K.

[Formula: see text][Formula: see text]TiO3 (BCT) single crystal has been widely studied as a promising lead-free ferroelectric material. In this work, high-quality BCT crystal was successfully grown by the Czochralski (CZ) method. The as-grown crystal is crack-free and shows black coloration. It possesses a high dielectric stability over a wide temperature range, while the dielectric loss is rather small below 90[Formula: see text]C. Furthermore, it possesses excellent ferroelectric properties with residual polarization strength ([Formula: see text]) and coercive field ([Formula: see text][Formula: see text]) of 17.93 [Formula: see text]C/cm2 and 8.47 kV/cm, respectively. Besides, BCT crystal shows large electromechanical coupling factors, with [Formula: see text][Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of 0.535, 0.254, 0.714 and 0.721, respectively. The piezoelectric coefficients [Formula: see text], [Formula: see text] and [Formula: see text] are measured to be − 36.5, 130 and 246 pC/N, respectively.

Single crystal fiber (SCF) is a novel solid gain medium and technique which combines the advantages of glass fiber and single crystal, showing great potential in the field of high-power lasers. In this paper, Er, Nd: YSGG single crystals with diameters of 2 mm and lengths of 80 mm were successfully grown using the micro-pulling-down method for the first time. Then, the measurements of Laue spots and Er3+ distribution indicated that the as-grown crystals were of a high quality. The effect of co-doped Nd3+ on the Er: YSGG was systematically discussed, which demonstrated that Nd3+ can decrease the fluorescence lifetime of Er: 4I13/2 that solve the self-termination bottleneck accordingly. These results demonstrate that Er, Nd: YSGG SCFs are promising materials for the further 3 μm laser generations.

Abstract Fabricating a heterojunction photodetector is efficient to take advantage of the built‐in electric field formed by heterojunction and thus improve the performance of photodetector. Herein, a CuZnS/Ga2O3 type‐II heterojunction photodetector is designed and constructed by chemical bath deposition for the first time. The photodetector exhibits super high rectifying characteristics (5.7 × 104 at ± 1 V), high responsivity (48.01 mA W−1 at 0 V), and detectivity (1.83 × 1012 Jones at 0 V), which are higher than most of the reported inorganic devices as far as the authors know. Benefiting from built‐in electric field constructed by the CuZnS/Ga2O3 type‐II heterojunction, the photo‐induced electron and hole pairs are quickly separated by the built‐in electric field between the Ga2O3 and the CuZnS interface. Therefore, the photodetector constructed by CuZnS/Ga2O3 type‐II heterojunction shows a prominent self‐powered performance. At zero bias, the photodetector shows a fast photoresponse (rise time τr = 70 ms, decay time τd = 10 ms). These data of performance are significantly excellent to most of the reported Ga2O3 heterojunction photodetectors. These performances strongly suggest that the CuZnS/Ga2O3 photodetector has great potential in ultra‐high performance self‐powered solar‐blind photodetector.

Owing to the advantages of ultra-wide bandgap and rich material systems, gallium oxide (Ga2O3) has emerged as a highly viable semiconductor material for new researches. This article mainly focuses on the growth processes, material characteristics, and applications of Ga2O3. Compared with single crystals and the epitaxial growth of other wide-bandgap semiconductors, large-size and high-quality β-Ga2O3 single crystals can be efficiently grown with a low cost, making them highly competitive. Thanks to the availability of high-quality single crystals, epitaxial films, and rich material systems, high-performance semiconductor devices based on Ga2O3 go through a booming development in recent years. The defects and interfaces of Ga2O3 are comprehensively analyzed owing to their significant influence on practical applications. In this study, the two most common applications of Ga2O3 materials are introduced. The high breakdown electric field, high working temperature, and excellent Baliga's figure-of-merit of Ga2O3 represent an inspiring prospect for power electronic devices. In addition, the excellent absorption in deep-ultraviolet band provides new ideas for optoelectronic detectors and ensures the dramatic progress. Finally, the summary, challenges, and prospects of the Ga2O3 materials and devices are presented and discussed.

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.

β-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 β-Ga2O3 nanostructures depends strongly on the growth temperature and time. Successful growth of β-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 β-Ga2O3. The bandgap of the β-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 β-Ga2O3 nanostructures. Strong photoluminescence emission in the UV-blue spectral region was obtained in the β-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 β-Ga2O3 nanostructures are expected to have potential applications in optoelectronic devices such as tunable UV–Vis photodetectors.

Abstract The edge-terminated Au/Ni/β-Ga2O3 Schottky barrier diodes were fabricated by using argon implantation to form the high-resistivity layers at the periphery of the anode contacts. With the implantation energy of 50 keV and dose of 5 × 1014 cm−2 and 1 × 1016 cm−2, the reverse breakdown voltage increases from 209 to 252 and 451 V (the maximum up to 550 V) and the Baliga figure-of-merit (VBR 2/Ron) also increases from 25.7 to 30.2 and 61.6 MW cm−2, about 17.5% and 140% enhancement, respectively. According to the 2D simulation, the electric fields at the junction corner are smoothed out after argon implantation and the position of the maximum breakdown electric filed, 5.05 MV/cm, changes from the anode corner at the interface to the overlap corner just under the implantation region. The temperature dependence of the forward characteristics was also investigated.

β−Ga2O3 field−effect transistors (FETs) were fabricated with and without local thinning to change the threshold voltage. A 220 nm Ga2O3 layer was mechanically exfoliated from a Cr−doped gallium oxide single crystal. Approximately 45 nm Ga2O3 was etched by inductively coupled plasma to form the local thinning. The threshold voltage of the device with etched local thinning increased from −3 V to +7 V compared to the unetched device. The effect of the local thinning was analyzed by device simulation, confirming that the local thinning structure is an effective method to enable enhancement−mode Ga2O3 FETs.

Empowered by an ultrawide bandgap (Eg = 4.5–4.9 eV), beta gallium oxide (β-Ga2O3) crystal is an ideal material for solar-blind ultraviolet (SBUV, λ < 280 nm) detection. Here, we report on the first demonstration of dual-modality SBUV light sensing integrated in the same device enabled by multi-physics coupling across photo-electrical and photo-thermo-mechanical domains. The specially designed suspended β-Ga2O3 nanoelectromechanical systems (NEMS) transducer reveals dual-modality responses, with a photocurrent responsivity of 4 mA/W and a frequency shift responsivity of 250 Hz/nW, upon SBUV light exposure. An additional demonstration of a β-Ga2O3 photo-field-effect transistor exhibits a boosted responsivity of 63 A/W. Analysis on the device suggests that reducing the thickness and length of the transducer could further improve the SBUV light sensing responsivities for both modalities. The demonstration could pave the way for future realization of SBUV detectors with dual modalities for enhanced detection fidelity, or respectively optimized for different sensing scenarios.

Single-crystal fibers (SCFs) have a great application potential in high-power lasers due to their excellent performance. In this work, high-quality and crack-free Yb3+:Lu3Al5O12 (Yb:LuAG) SCFs were successfully fabricated by the micro-pulling-down (μ-PD) technology. Based on the laser micrometer and the X-ray Laue diffraction results, these Yb:LuAG SCFs have a less than 5% diameter fluctuation and good crystallinity along the axial direction. More importantly, the distribution of Yb ions is proved to be uniform by electron probe microanalysis (EPMA) and the scanning electron microscope (SEM). In the laser experiment, the continuous-wave (CW) output power using a 1 mm diameter Yb:LuAG single-crystal fiber is determined to be 1.96 W, at the central wavelength of 1047 nm, corresponding to a slope efficiency of 13.55%. Meanwhile, by applying a 3 mm diameter Yb:LuAG SCF, we obtain a 4.7 W CW laser output at 1049 nm with the slope efficiency of 22.17%. The beam quality factor M2 is less than 1.1 in both conditions, indicating a good optical quality of the grown fiber. Our results show that the Yb:LuAG SCF is a potential solid-state laser gain medium for 1 μm high-power lasers.

In this letter, MOS capacitors with bilayer dielectrics consisted of large bandgap Al2O3 and high-k HfO2 in different stacking order on n-type doped (100) β-Ga2O3 are investigated through C − V and J − V measurement. The C − V measurement results reveal that incoming HfO2 makes both bilayer structures attain an increasing dielectric constant, which means a better gate control ability in transistors comparing with single Al2O3. Additionally, the interface state density extracted by high-low frequency capacitance method suggests that Al2O3/(100)β-Ga2O3 with no treatment shows a comparative Dit value (8.0 × 1012 cm-2eV-1 to 2.2 × 1011 cm-2eV-1) with HfO2/(100)β-Ga2O3 (8.4 × 1012 cm-2eV-1 to 1.0 × 1011 cm-2eV-1) in energy range of 0.2 to 0.9 eV. Furthermore, HfO2/Al2O3/Ga2O3 showing a bigger forward breakdown voltage of 11.0 V than 7.8 V of Al2O3/HfO2/Ga2O3 demonstrates that inserted larger bandgap Al2O3 insulator between Ga2O3 semiconductor and high-k HfO2 dielectric can prevent gate leakage current more effectively. Accordingly, the HfO2/Al2O3/Ga2O3 can enhance gate control ability with an acceptable gate breakdown voltage and become an alternative choice in the design of the gate structure for Ga2O3 MOSFETs.

β-Ga2O3 is an ultra-wide bandgap semiconductor with applications in power electronic devices. Revealing the transport characteristics of β-Ga2O3 devices at various temperatures is important for improving device performance and reliability. In this study, we fabricated a Pt/β-Ga2O3 Schottky barrier diode with good performance characteristics, such as a low ON-resistance, high forward current, and a large rectification ratio. Its temperature-dependent current–voltage and capacitance–voltage characteristics were measured at various temperatures. The characteristic diode parameters were derived using thermionic emission theory. The ideality factor n was found to decrease from 2.57 to 1.16 while the zero-bias barrier height Φb0 increased from 0.47 V to 1.00 V when the temperature was increased from 125 K to 350 K. This was explained by the Gaussian distribution of barrier height inhomogeneity. The mean barrier height Φ ¯ b0 = 1.27 V and zero-bias standard deviation σ0 = 0.13 V were obtained. A modified Richardson plot gave a Richardson constant A* of 36.02 A·cm−2·K−2, which is close to the theoretical value of 41.11 A·cm−2·K−2. The differences between the barrier heights determined using the capacitance–voltage and current–voltage curves were also in line with the Gaussian distribution of barrier height inhomogeneity.

Single crystal fibers of 30% Er3+-doped compound of Y3(ScxGa1−x)5O12 have been grown by using the micro-pulling down (μ-PD) technique successfully. Our main purpose is to tune the fluorescence properties by adjusting the ratios of Sc3+ and Ga3+ ions inside the matrix crystals. The crystal structures of the series compounds were measured and analyzed through X-ray diffraction (XRD) measurements. The components and doping elements distributions were measured by the X-ray Fluorescence spectrometry and electron-probe microanalyzer. The absorption and mid-infrared fluorescence spectra, including the fluorescent lifetime of Er3+:4I13/2 and 4I11/2 levels were measured and compared systematically at room temperature. Spectral analysis indicated that the fluorescent lifetime of Er3+:4I13/2 tended to shorten and the emission spectra began to show a red shift when the proportion of YSG increased in the compound. Furthermore, the Raman spectra were measured to reveal the variations of lattice vibration and phonon energy.

Calcium yttrium aluminate (CaYAl3O7) crystal was grown and characterized in detail for high temperature piezoelectric sensors for the first time. The thermal properties of the CaYAl3O7 (CYAM) crystal were investigated systematically. In particular, the CYAM crystal exhibits considerably high resistivity along X- and Z- direction in the order of 6.96 × 107 Ω·cm and 2.86 × 108 Ω·cm at 600 °C, respectively. The temperature dependence of the electromechanical properties of CYAM crystal were investigated over the temperature range of 25–500 °C. The high thermal stability of piezoelectric properties together with its high electrical resistivity, makes CaYAl3O7 crystal a promising candidate for high temperature piezoelectric applications.

2 μm pulsed lasers not only have critical applications in military, medical, and processing fields but are also an important frontier in laser physics. The development of these pulsed lasers has been hindered by the lack of laser crystals with both high thermal conductivity and broad spectral properties. In this work, Tm, Ho:CaGdAlO4 disordered crystal with ultra-broad emission spectra around 2 μm was achieved successfully by modulating the emission intensities of Tm3+ and Ho3+ ions to the same level. The FWHM of the absorption spectra at 793 nm for the <001> and <100> directions are 18.69 and 19.44 nm, respectively, which is beneficial for commercial laser diode pumping. More importantly, the FWHM of the emission spectrum is 264 nm, which is the widest one reported in the previous literature. The results indicate that the Tm, Ho:CaGdAlO4 crystal with its broader spectra has the potential to generate an ultrashort pulse laser. [ABSTRACT FROM AUTHOR]

In order to balance the contradiction between on and off performances of the Schottky diodes, Si-doped β-(AlxGa1-x)2O3 (β-AlGaO) single crystals were designed based on the bandgap and impurity engineering of β-Ga2O3. The bandgap became larger with Al element doping. The photoluminescence properties of Si-doped β-AlGaO were measured and the emission band was separated into three Gaussian peaks with wavelengths of 372 nm, 410 nm, and 453 nm. These peaks were derived from a self-trapped hole (STH), (VGa + VO)1-, and VGa 2-, respectively. This demonstrated that Al only acted on valence and conduction bands, without introducing intermediate transition levels, indicating excellent bandgap regulation. The thermal properties of Si-doped β-AlGaO were demonstrated for the first time. Noticeably, a carrier concentration of 4.61 X 1018 cm-3 and a resistivity of 0.099 O cm were observed at room temperature in Si-doped b-AlGaO. At low temperatures, the dominant mechanism was ionized impurity scattering, while at high temperatures, optical phonon scattering became dominant. The on-resistance of Schottky barrier diodes (SBDs) prepared using this material was only 1.57 mO cm², and the Schottky barrier was as high as 1.21 eV. At similar Schottky barrier heights, the on-resistance was 10 times lower compared to β-Ga2O3 based SBDs. In addition, the device has a high forward current density (J@2V) of 521 A cm-2 at a forward voltage of 2.0 V and an ON-/OFF-current ratio of up to 109. This work presents a viable approach for fabricating high-performance vertical structure devices using Si-doped β-AlGaO materials based on the bandgap structure and impurity engineering. [ABSTRACT FROM AUTHOR]