Edge-defined Film-fed Growth Method Research Articles

Investigation of the crack extending downward along the seed of the β-Ga2O3 crystal grown by the EFG method

The formation mechanism of the crack and its effect on the crystal quality of β-Ga2O3 grown by the edge-defined film-fed growth method.

2-Dimensional Ga2O3 Based Field Effect Transistor for Hydrogen Sensing Application

β-phase gallium oxide (β-Ga2O3) has attracted a lot of interest for the applications of high-power electronics, gas sensors, and solar-blind photodetectors. β-Ga2O3 is an alternative semiconducting material for high-power and high-temperature devices due to a large bandgap energy of 4.9 eV and high critical breakdown field (> 8 MV/cm). The Baliga’s figure of merit is 3400, which is 4-10 times higher than those of GaN and SiC. Ga2O3 based devices is expected to be more efficient with reduced size and high level of integration because the theoretical on-state resistance is almost one order magnitude lower than those of GaN and SiC devices at the same breakdown voltage. When compared to GaN and SiC, single crystal Ga2O3 wafers are available at low cost with floating zone and the edge-defined film-fed growth methods. The monoclinic β-Ga2O3 is the most stable form among five different crystal phases of Ga2O3. The large lattice constant of 12.23 Å of β-Ga2O3 along [100] direction enables to achieve the facile cleavage of β-Ga2O3 crystal into 2-dimensional flake though β-Ga2O3 is not a Van der Waals material. The thin channel of Ga2O3 flake is beneficial to the FET (field effect transistor) type gas sensor. In this study, the fabrication of 2-dimensional β-Ga2O3 flake based field effect transistor and its hydrogen sensing characteristics for hydrogen sensor application will be presented.

Growth and spectroscopic properties of Tm3+ and Tb3+ co-doped GdScO3 crystal

GdScO3 single crystal codoped with Tm3+ and Tb3+ ions was successfully grown by the Edge-defined Film-fed Growth Method (EFG) for the first time. Absorption, fluorescence spectrum and fluorescence lifetimes of the grown crystal at room temperature were measured. The absorption cross-section at 789 nm was calculated to be 8.20 × 10−21 cm2. The emission cross-section was 1.35 × 10−21 cm2 at 1504 nm with the FWHM of 95.3 nm. The fluorescence lifetimes of the 3H4 state and the 3F4 state were fitted to be 253 μs and 1460 μs, respectively. Compared with Tm3+ single doped GdScO3 crystal, the codoping of Tb3+ successfully depopulated the 3F4 energy level and enhanced the emission at 1.5 μm region. It indicated that Tm,Tb:GdScO3 could be favorable laser medium for 1.5 μm-laser operation.

Raman and photoluminescence properties of un-/ion-doped β-Ga2O3 single-crystals prepared by edge-defined film-fed growth method

In this paper, β-Ga2O3 single-crystal with three different (100), (010) and (001) orientations and Si-/Mg-/Fe-/Sn-doped are synthesized by EFG method. β-Ga2O3 is investigated by confocal Raman and PL spectroscopy. Raman results indicated that 3D Ga2O3 substrates in the cases of un-/ions-doped growth have superior crystallinity and high uniformity. The possible reasons for the shift and broadening of vibration modes at the typical Ag (3), Ag (6) and Ag (10) mode are mainly caused by ions doping. Ga2O3(001) has a stronger vibration and translation mode of GaIO4 chain at the Ag (3) mode, in contrast to un-doped (100)/(010) planes. The Ag (10) mode change in Mg-doped (100) is significant, which means that Mg atoms are the most likely to substitute GaII atoms in the center of GaIIO6 octahedron. In PL spectroscopy, Sn-doped samples show wider blue-green emission in the range of 350–650 nm, which are related to the defect emission of Ga2O3 and Sn-doped nsnp-ns2 transition.

Optical investigation of Pr3+ doped CsSrI3 single crystals grown by EFG method

Current interest in halide scintillation crystals is ABX3:Eu (A = Cs, B = Ca, Sr, X = Cl, Br, I) material family. Among them, CsSrI3:Eu has been widely studied, but we still hope to study the performance of other ion-doped CsSrI3 crystals. In this work, we report the CsSrI3:Pr crystals with various Pr3+ concentrations are grown by Edge-defined Film-fed Growth (EFG) method for the first time. As Pr3+-doped CsSrI3 single crystal is non-equivalent substitution (Pr3+ → Sr2+), it may affect the growth and luminescent properties of the crystal. We have grown the CsSrI3:Eu and CsSrI3:Pr crystals and compared them with the decay time. By comparison, we found that Pr-doped CsSrI3 crystals has a better decay time than CsSrI3:Eu crystals.

Multiple shaped-crystal growth of oxide scintillators using Mo crucible and die by the edge defined film fed growth method

Abstract Edge defined Film Fed Growth (EFG) method with molybdenum (Mo) crucible and die was studied for the growth of several oxide-based single crystals. At first, reactivity between the molybdenum (Mo) metal and oxide melts of Ce:(Lu,Y)2SiO5 (LYSO) Ce:Y2SiO5 (YSO), Ce:Gd3(Al,Ga)5O12 (GAGG), Ce:Lu3Al5O12 (LuAG), Ce:Y3Al5O12 (YAG) was investigated. The experimental and calculation results on the reactivity with Mo show that the aluminum garnets (LuAG, YAG) had the smallest reactivity with Mo metal. On the contrary, GAGG showed the strongest reaction with Mo. Then, the multiple-die grown shaped single crystal growth of Ce:LuAG was demonstrated by EFG method. Single crystal plates up to 320 mm in length were grown successfully. The homogeneity of dopant distribution, Mo contamination, luminescence and scintillation responses of the grown crystals were evaluated.

Defects and Optical Property of Single-crystal Sapphire Fibers Grown by Edge-defined Film-fed Growth Method

Defects and Optical Property of Single-crystal Sapphire Fibers Grown by Edge-defined Film-fed Growth Method

X-ray diffraction and Raman characterization of β-Ga2O3 single crystal grown by edge-defined film-fed growth method

The crystallinity and wafer uniformity of (2¯01) and (010) oriented β-Ga2O3 substrates grown by edge-defined film-fed growth (EFG) were investigated by laboratory X-ray diffraction (XRD), synchrotron XRD, polarized Raman spectroscopy, and Raman mapping. XRD results indicated that the EFG substrates had superior crystallinity and high uniformity. Position-dependent XRD ω-rocking curves recorded across a 50.8-mm-diameter substrate had small standard deviations of δF = 1.6% for the full width at half maximum and δP = 2.8% for the peak intensity. The radius of curvature was measured to be 37.7 m for the (2¯01) substrate and 16.4 m for the (010) substrate. The results of synchrotron XRD with various beam sizes suggested that the curving of crystal planes was mainly along the [010] growth direction rather than along the [102] direction. Raman spectra showed that Sn doping up to 3.3 × 1018 cm−3 did not give rise to a notable Raman peak shift. The strain distribution evaluated by Raman mapping implied the high uniformity of both (2¯01) and (010) substrates. From these results, it was concluded that β-Ga2O3 ingots grown by EFG have high crystallinity and can be treated as three-dimensionally uniform bulk crystals in the cases of both undoped and Sn-doped growth.

High-speed growth of CsSr1-xEuxI3 (x = 003, 005, 007) single crystals by the edge-defined film-fed growth method

CsSrI3:3%Eu (Φ10×55mm), CsSrI3:5%Eu (Φ10×50mm) and CsSrI3:7%Eu (Φ10×45mm) single crystals have been successfully grown by the edge-defined film-fed growth method for the first time, with the growth rate reaching 10-20mm/h. We designed a crystal growth device that achieved the first growth of this binary scintillation crystal by the EFG method. The raw material purification, temperature gradient of experimental device and growth rate, which are the effect factors of crystal quality, were systematically investigated. Moreover, the effect of Eu2+ concentration on optical properties were studied. The Eu2+ 5d-4f emission band was observed at 450-455nm, and the PL decay time was determined as 1.32µs for CsSrI3:3%Eu, 1.35µs for CsSrI3:5%Eu and 0.73µs for CsSrI3:7%Eu.

Surface defects in EFG sapphire single crystals

Single crystal growth by the edge-defined film-fed growth method (EFG) has been commercially practiced for over 40 years. State of the art sapphire crystals can be over 300 mm wide, 10 mm thick and 1 m long. In addition to well-known defects such as bubble inclusions and bulk structure loss, we describe a crystalline defect occurring uniquely at the outer surfaces of the sapphire panel. Termed ‘surface crystals’, they penetrate less than 1 mm into the depth of the A-plane panel and can originate and terminate multiple times in a single panel. We report correlations with both temperature and ambient conditions and present micro-scale characterization to elucidate the nature of these defects.

X-ray Detection Performance of Vertical Schottky Photodiodes Based on a Bulk β-Ga2O3 Substrate Grown by an EFG Method

In this study, we investigated the X-ray detection capabilities of vertical β-Ga2O3 Schottky photodiodes on a bulk (100) β-Ga2O3 substrate that was grown by an edge-defined film-fed growth (EFG) method. Both the static and transient responses of the fabricated detectors to X-ray illumination were characterized, and a strong trap-related photoconductive effect was observed in addition to the photovoltaic mechanism. The responsivity of the detectors was calculated to be 1.8 μC/Gy at a reverse bias of −25.8 V. The response time was studied though fitting the transient photocurrent using the exponential decay functions. Associated with material characterizations, it was revealed that the existence of oxygen vacancies within the β-Ga2O3 substrate weakened the performances of the X-ray detectors, mainly their sensitivity and response speed.

Numerical Analysis of Thermal Stress in Semi‐Transparent Oxide Crystals Grown by Czochralski and EFG Methods

AbstractCrystal growth of oxides is generally difficult since large curvatures of the growth interface in these systems generate high thermal stress, dislocations and crystal cracking. Three‐dimensional numerical modeling is applied to investigate thermal stress distribution in sapphire and langatate La3Ta0.5Ga5.5O14 (LGT) semi‐transparent crystals grown by Czochralski (Cz) and Edge‐defined Film‐fed Growth (EFG) techniques. The analysis of thermal stress distribution in a sapphire ingot grown in a Czochralski furnace shows high von Mises stresses distributed almost symmetrically on large areas in the crystal. Thermal stress computations for piezoelectric langatate crystals grown in a Czochralski configuration show non‐symmetrical von Mises distribution with higher stress on one side of the ingot. These numerical results are in agreement with experimental results showing non‐symmetrical cracking at the outer surface of the crystal. 3D modeling of multi‐die EFG growth of white sapphire ribbons shows that the von Mises stress is almost constant when the number of ribbons is increased from two to ten. Two models are applied to simulate the internal radiative heat transfer in the sapphire crystals: P1 approximation and the Rosseland radiation model. Numerical results show that applying Rosseland formula introduces significant errors in temperature field calculations especially in the case of the EFG configuration.

Temperature Gradient Designing and Optical Properties of SrI2 and SrI2:Eu Crystals Grown by Edge-Defined Film-Fed Growth (EFG) Method

In this work, SrI2 and SrI2:Eu5% single crystals with size of O10 × 60 mm3 and O10 × 30 mm3 were successfully grown by edge-defined film-fed growth (EFG) method. In the crystal growth process, the crack and turbidity of the crystal were solved by designing a temperature field, thereby optimizing crystal quality and obtaining crack-free crystals. X-ray diffraction analysis was performed on the grown crystals, and the optical properties of these crystals have been investigated at room temperature. Under the excitation of ultraviolet (UV) light, the crystals exhibit a single luminescence peak centered at 435 nm (λex = 350 nm), and the photoluminescence (PL) decay time is 0.594 μs. In addition, the designed temperature field also provides a reference value for other crystals grown by EFG method.

Preparation and Properties of Sapphire by Edge-defined Film-fed Growth (EFG) Method with Different Growth Directions

Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed (c-sapphire) and a-[11-20] seed (a-sapphire) were used to prepare sapphire by edge-defined film-fed growth (EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×103 and 3.9×103 cm-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid (SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.

Growth and characterization of 2-inch high quality β-Ga2O3 single crystals grown by EFG method

β-Ga2O3 is an ultra-wide band-gap semiconductor with promising applications in UV optical detectors, Schottky barrier diodes, field-effect transistors and substrates for light-emitting diodes. However, the preparation of large β-Ga2O3 crystals is undeveloped and many properties of this material have not been discovered yet. In this work, 2-inch β-Ga2O3 single crystals were grown by using an edge-defined film-fed growth method. The high quality of the crystal has been proved by high-resolution X-ray diffraction with 19.06 arcsec of the full width at half maximum. The electrical properties and optical properties of both the unintentionally doped and Si-doped β-Ga2O3 crystals were investigated systematically.

Ti-Doped β-Ga2O3: A Promising Material for Ultrafast and Tunable Lasers

As we know, Ti3+:Al2O3 is a very famous crystal for ultrafast and tunable lasers. However, it also has disadvantages including small segregation coefficient and short fluorescence lifetime of Ti3+. For comparison, Ti-doped β-Ga2O3 (Ti3+:β-Ga2O3) single crystals with good spectral properties have been designed and grown successfully by edge-defined film-fed growth method with larger segregation coefficient and longer fluorescence lifetime. The segregation coefficient of Ti3+ ions in the Ti3+:β-Ga2O3 crystal was calculated to be 0.49, which was much larger than that in Ti3+:Al2O3 (0.2). The thermal conductivity of Ti3+:β-Ga2O3 crystal was measured to be 24.7 W/mK along the ⟨010⟩ direction at room temperature, which is very attractive as a laser crystal. Furthermore, the polarized absorption spectra and fluorescence spectra of Ti3+:β-Ga2O3 were measured and analyzed. The full width at half-maximum of the emission peak was as large as 140 nm. The fluorescence lifetime was up to 176 ± 5 μs, which was about 50 ...

A comparative study of wet etching and contacts on [formula omitted] and (010) oriented β-Ga2O3

We report on the effect of β-Ga2O3 crystal orientation on wet etching and Ohmic contact formation. The photochemical etching rate in KOH solutions of (2¯01) oriented, n-type bulk single crystals grown by the edge-defined film-fed growth method is ∼3–4 times higher than for the (010) planes. The activation energy for etching was 0.498 eV and 0.424 eV for (2¯01) and (010) orientations, respectively, suggesting the etching is reaction-limited with the same rate-limiting step. Ti (200 Å)/Au (1500 Å) metallization deposited on the two different orientations and annealed at 450 °C showed Ohmic current-voltage (I-V) behavior for (2¯01) but rectifying characteristics for (010). For (010) Ga2O3, there exists 2 types of surfaces having Ga and O atomic densities of 0.58 and 0.87 × 1015 cm−2, respectively. By contrast, for (2¯01) Ga2O3 surfaces, there exist 2 types of surface, with each type terminated with only Ga or O. If the surface is terminated with O, the dangling bond densities of O are 1.78 and 2.68 × 1015 cm−2, respectively. We found that (2¯01)–oriented Ga2O3 is etched at higher rates and is easier to form Ohmic contacts than (010) Ga2O3. The higher density of oxygen dangling bonds on the (2¯01) plane correlates with the faster etch rates and pronounced Ohmic behavior from deposited metals.

(Invited) Ultrawide Bandgap β-Ga2O3 Thin Films: Growths, Properties and Devices

Ultrawide bandgap (UWBG) gallium oxide (Ga2O3) represents an emerging semiconductor material with excellent chemical and thermal stability up to 1400 oC. It has a band gap of 4.5-4.9 eV, much higher than that of the GaN (3.4 eV) and 4H-SiC (3.2 eV). It exhibits high transparency in the deep ultraviolet (DUV) and visible wavelength region due to its very large bandgap. The monoclinic b-phase Ga2O3 represents the thermodynamically stable crystal among the known five phases (α, β, γ, δ, ε). The breakdown field of β-Ga2O3 is estimated to be 8 MV/cm, which is about three times larger than that of 4H-SiC and GaN. These unique properties make β-Ga2O3 a promising candidate for high power electronic device and solar blind photodetector applications. More advantageously, single crystal β-Ga2O3 substrates can be synthesized by scalable and low cost melting based growth techniques such as edge-defined film-fed growth (EFG), floating zone (FZ) and czochralski methods. For β-Ga2O3 thin film synthesis, both molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) have been demonstrated to produce high quality and controllable doping films but with slow growth rates (2-10 nm/min). Halide vapor phase epitaxy (HVPE) using chloride precursors was demonstrated to grow β-Ga2O3 films with fast growth rates (>5 μm/hr). Recently, we have developed a low pressure chemical vapor deposition (LPCVD) method to grow high quality β-Ga2O3 thin films on both native Ga2O3and c-sapphire substrates with controllable doping and fast growth rates up to 10 μm/hr. In this talk, we present a study on the defects in β-Ga2O3 thin films grown via LPCVD. The β-Ga2O3 thin films were grown on native β-Ga2O3 substrates and sapphire substrates using high purity gallium and oxygen as the precursors, and argon (Ar) as the carrier gas. The growth temperature ranged between 850 ˚C and 950 ˚C. The β-Ga2O3 thin films were characterized by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). FESEM images were taken with Helios 650. High resolution transmission electron microscopy (HRTEM) images and selected-area electron diffraction (SAED) were taken using a FEI Tecnai F30 at 300 kV. Bright field, dark field, combined with two-beam condition TEM were used to characterize the defects in the as-grown films. From our studies, β-Ga2O3 thin films grown on (010), (001) and (-201) β-Ga2O3 substrates have shown different growth rates as well as different properties of interfacial defects. Improved LPCVD growths to suppress defects in β-Ga2O3thin films grown on different substrates will be discussed. Room temperature Hall measurements will be performed to understand the dependence of carrier transport on defects. In summary, the fundamental defect studies are performed on β-Ga2O3 thin films grown via LPCVD on Ga2O3 and sapphire substrates. The results from this study are important knowledge for power device applications.

Growth of homogeneous Nd:LGGG single crystal plates by edge-defined film-fed growth method

Device-size Nd3+:(LuxGd1−x)3Ga5O12 (Nd:LGGG) single crystal plates have been grown by edge-defined film-fed growth (EFG) method for the first time. The problems encountered during the crystal growth have been discussed and solved, resulting in a single crystal plate with a length of 180mm. In particular, the evaporation loss of Ga2O3 composition during the crystal growing has been depressed efficiently by using an Ir lid. The crystal perfection was confirmed by X-ray rocking curve with a FWHM of the 32arcsec, meaning a high crystalline quality. It was very interesting to find that the distribution of Nd3+ in the crystal grown by EFG method was more homogeneous than that in Cz method, benefitting from the larger segregation coefficient of Nd3+ in EFG method. The thermal conductivity was measured to be 8.1Wm−1K−1 at room temperature. All the properties showed that the Nd:LGGG crystal plates grown by EFG method were promising for high power laser application.

Development and melt growth of novel scintillating halide crystals

Melt growth of scintillating halide crystals is reviewed. The vertical Bridgman growth technique is still considered as very popular method that enables production of relatively large and commercially attractive crystals. On the other hand, the micro-pulling-down method is preferable when fabrication of small samples, sufficient for preliminary characterization of their optical and/or scintillation performance, is required. Moreover, bulk crystal growth is also available using the micro-pulling-down furnace. The examples of growths of various halide crystals by industrially friendly melt growth techniques including Czochralski and edge-defined film-fed growth methods are also discussed. Finally, traveling molten zone growth that in some degree corresponds to horizontal zone melting is briefly overviewed.