Ga Precursor Research Articles

Growth and performance of n++ GaN cap layer for HEMTs applications

Apart from providing high-quality ohmic contacts to III-N devices, n++ GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 °C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 × 1019 cm−3 and mobility of 103 cm2/Vs. Moreover, electron concentration in the range of 1020 cm−3 is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 × 1019 cm−3) and 8 nm thick (Si: 7.2 × 1019 cm−3) n++ GaN cap is implemented in normally-off n++ GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n++ GaN cap can shield the channel from the unstable surface potential.

Deposition Kinetics and Characteristics of Peald Igzo Films Using Tetrahydrofuran-Adducted in & Ga Precursors

As the down-scaling of semiconductor materials, silicon compatible emerging materials have extensively researched for next generation display and 3D structured devices. In particular, oxide semiconductors are considered a promising candidate for backplane applications in display. Among them, indium-gallium-zinc oxide (IGZO) using plasma enhanced atomic layer deposition (PEALD) has excellent properties, like high mobility, low leakage current, high transparecy and low temperature processablility. However, conventional precursors for IGZO still have some prolems to solve such as low deposition rate, low thermal stability and high price. In this study, we developed indium precursor (Trimethylindium Tetrahydrofuran, DIP-4) and gallium precursor (Trimethylgallium Tetrahydrofuran, DGP-2) to overcome the shortcomings of the conventional In & Ga precursors. ALD characteristics of the films deposited using the newly developed the precursors were confirmed through the source feeding time saturation and linearity. Furthermore, the incubation time of In, Ga and Zn oxide films according to the different bottom layer was respectively verified and calculated using the developed DIP-4, DGP-2 and commercially used DEZn. In order form a multilayer IGZO thin film, application of the incubation factors at IGZO process were experimentally demonstrated. Thickness of the IGZO films can be easily controlled through modulation of the incubation factors. The physical and chemical properties of the films were analyzed by X-ray diffraction, X-ray reflectrometer, X-ray photoelectron spectroscopy, transmission electron microscope. Figure 1

Fabrication of Al doped α-GaOOH nanorod arrays on FTO for self-powered photoelectrochemical solar-blind UV photodetectors

Al doped α-GaOOH nanorod arrays were grown on FTO via hydrothermal processes by using gallium nitrate and aluminum nitrate mixed aqueous solutions with fixed 1:1 mole ratio as precursors. With increasing the gallium nitrate precursor concentrations, the Ga/Al atom ratios in nanorod arrays increase from 0.36 to 2.08, and the length becomes much longer from 650 nm to 1.04 μm. According to the binding energy difference between Ga 2p3/2 core level and its background in x-ray photoelectron spectroscopy, the bandgap is estimated to be around 5.3 ± 0.2 eV. Al doped α-GaOOH nanorod array/FTO photoelectrochemical photodetectors show enhanced self-powered solar-blind UV photodetection properties, with the decrease of Ga precursor concentrations. The maximum responsivity at 255 nm is 0.09 mA W−1, and the fastest response time can reach 0.05 s. The improved photoresponse speed is ascribed from much shorter transportation route, accelerated carrier recombination by recombination centers, and smaller charge transfer resistance at the α-GaOOH/electrolyte interface with decreasing the gallium nitrate precursor concentrations. The stability and responsivity should be further improved. Nevertheless, this work firstly demonstrates the realization of self-powered solar-blind UV photodetection for α-GaOOH nanorod arrays on FTO via Al doping.

Investigation of Si incorporation in (010) β-Ga2O3 films grown by plasma-assisted MBE using diluted disilane as Si source and suboxide Ga2O precursor

Traditionally, elemental Ga and Si have been used to supply Ga and Si, respectively, in molecular beam epitaxy (MBE) to grow Si-doped β-Ga2O3. In this work, we investigated the feasibility of enhancing the β-Ga2O3 growth rate by using a Ga-suboxide precursor in a plasma-assisted MBE. Additionally, Si doping of β-Ga2O3 using diluted disilane and Ga-suboxide as the Si and Ga precursors, respectively, was studied. The growth rate and film quality under different suboxide fluxes were inspected. We found that Si concentration has an inverse relationship with Ga2O flux due to atom competition. A room-temperature mobility of 115 cm2/V s was measured for an electron concentration of 1.2 × 1017 cm−3 on the sample grown using a Ga2O beam equivalent pressure of 1.1 × 10−7 Torr and a disilane flow rate of 0.006 sccm. Temperature-dependent Hall characterization was performed on this sample, revealing compensating acceptor and neutral impurity densities of 2.70 × 1015 and 8.23 × 1017 cm−3, respectively.

Cationic dinuclear complexes [M2(PCP)2μ-Cl][GaCl4] of the group 10 elements. metallophilic interactions and catalytic dehydrogenation of Me2NHBH3.

The facile synthesis of the cationic dinuclear group 10 complexes [M2(PCP)2μ-Cl]+ (M = Ni, Pd, Pt) by transmetallation from a simple Ga precursor is reported (PCP = 2,6-(Ph2P)C6H3). Their use for the catalysed dehydrogenation of Me2NHBH3 shows that Ni has a higher reactivity than Pt, whereas Pd is inactive.

Thermal Atomic Layer Deposition of Gallium Nitride Films Using Tris(dimethylamido)Gallium and Ammonia

Gallium nitride (GaN) is a III-V semiconductor material with a wide and direct bandgap, relatively high carrier mobility, and high breakdown voltage. GaN is suitable for applications in optoelectronic devices and power devices, including light-emitting diodes (LEDs) and high electron mobility transistors (HEMTs). Typically, epitaxial GaN layers are grown by metal-organic chemical vapor deposition (MOCVD) at high deposition temperatures. However, low-temperature growth of GaN is necessary for temperature-sensitive devices and substrates. Atomic layer deposition (ALD) is a technique that offers unique advantages, such as low process temperature, excellent conformality, and atomic-level thickness control.In this study, we investigated the thermal ALD process of GaN at a low temperature of 200°C. Tris(dimethylamido)gallium (TDMAGa) was selected as the Ga precursor because tris(dimethylamido)titanium and tris(dimethylamido)aluminum were successfully adopted in the low-temperature ALD process of TiN and AlN thin films [1]. The growth and properties of ALD GaN films were investigated. ALD GaN films exhibited a self-limiting reaction with a deposition rate of 1.34 Å/cycle at 200°C, with a refractive index of 2.07. The saturation times for TDMAGa and NH3 pulses were 5 s and 30 s, respectively. Deposition at 250°C showed a deposition rate higher than 3 Å/cycle due to the thermal decomposition of TDMAGa. The ALD GaN film deposited at 200°C was amorphous and nitrogen deficient. To improve the crystallinity and composition, the as-deposited GaN films were annealed in an NH3 atmosphere in the deposition chamber without air exposure. The effects of annealing on the crystallinity and composition of the films were investigated. Acknowledgments This work was supported by Samsung Display Co., Ltd.

Transferable Force Field for Gallium Nitride Crystal Growth from the Melt Using On-The-Fly Active Learning.

Atomic-scale simulations of reactive processes have been stymied by two factors: the lack of a suitable semiempirical force field on one hand and the impractically large computational burden of using ab initio molecular dynamics on the other hand. In this paper, we use an "on-the-fly" active learning technique to develop a nonparameterized force field that, in essence, exhibits the accuracy of density functional theory and the speed of a classical molecular dynamics simulation. We developed a force field capable of capturing the crystallization of gallium nitride (GaN) during a novel additive manufacturing process featuring the reaction of liquid Ga and gaseous nitrogen precursors to grow crystalline GaN thin films. We show that this machine learning model is capable of producing a single force field that can model solid, liquid, and gas phases involved in the process. We verified our computational predictions against a range of experimental measurements relevant to each phase and against ab initio calculations, showing that this nonparametric force field produces properties with excellent accuracy as well as exhibits computationally tractable efficiency. The force field is capable of allowing us to simulate the solid-liquid coexistence interface and the crystallization of GaN from the melt. The development of this transferable force field opens the opportunity to simulate the liquid-phase epitaxial growth more accurately than before to analyze reaction and diffusion processes and ultimately to establish a growth model of the additive manufacturing process to create the gallium nitride thin films.

Analysis of Hazy Ga- and Zr-Co-Doped Zinc Oxide Films Prepared with Atmospheric Pressure Plasma Jet Systems.

Co-doped ZnO thin films have attracted much attention in the field of transparent conductive oxides (TCOs) in solar cells, displays, and other transparent electronics. Unlike conventional single-doped ZnO, co-doped ZnO utilizes two different dopant elements, offering enhanced electrical properties and more controllable optical properties, including transmittance and haze; however, most previous studies focused on the electrical properties, with less attention paid to obtaining high haze using co-doping. Here, we prepare high-haze Ga- and Zr-co-doped ZnO (GZO:Zr or ZGZO) using atmospheric pressure plasma jet (APPJ) systems. We conduct a detailed analysis to examine the interplay between Zr concentrations and film properties. UV-Vis spectroscopy shows a remarkable haze factor increase of 7.19% to 34.8% (+384%) for the films prepared with 2 at% Zr and 8 at% Ga precursor concentrations. EDS analysis reveals Zr accumulation on larger and smaller particles, while SIMS links particle abundance to impurity uptake and altered electrical properties. XPS identifies Zr mainly as ZrO2 because of lattice stress from Zr doping, forming clusters at lattice boundaries and corroborating the SEM findings. Our work presents a new way to fabricate Ga- and Zr-co-doped ZnO for applications that require low electrical resistivity, high visible transparency, and high haze.

High-speed growth of thick high-purity β-Ga2O3 layers by low-pressure hot-wall metalorganic vapor phase epitaxy

High-speed growth of thick, high-purity β-Ga2O3 homoepitaxial layers on (010) β-Ga2O3 substrates by low-pressure hot-wall metalorganic vapor phase epitaxy was investigated using trimethylgallium (TMGa) as the Ga precursor. When the reactor pressure was 2.4–3.4 kPa, the growth temperature was 1000 °C, and a high input VI/III (O/Ga) ratio was used, the growth rate of β-Ga2O3 could be increased linearly by increasing the TMGa supply rate. A thick layer was grown at a growth rate of 16.2 μm h−1 without twinning. Incorporated impurities were not detected, irrespective of the growth rate, demonstrating the promising nature of β-Ga2O3 growth using TMGa.

Promoter deletion in the soybean Compact mutant leads to overexpression of a gene with homology to the C20-GA 2-oxidase family.

Height is a critical component of plant architecture, significantly affecting crop yield. The genetic basis of this trait in soybean remains unclear. In this study, we report the characterization of the Compact mutant of soybean which has short internodes. The candidate gene was mapped to chromosome 17, and the interval containing the causative mutation was further delineated using biparental mapping. Whole-genome sequencing of the mutant revealed an 8.7kb deletion in the promoter of the Glyma.17g145200 gene, which encodes a member of the class III gibberellin 2-oxidases. The mutation has a dominant effect, likely via increased expression of the GA 2-oxidase transcript observed in green tissue, as a result of the deletion in the promoter of Glyma.17g145200. We further demonstrate that levels of GA precursors are altered in the Compact mutant, supporting a role in gibberellin metabolism, and that the mutant phenotype can be rescued with exogenous GA3. We also determined that overexpression of Glyma.17g145200 in Arabidopsis results in dwarfed plants. Thus, gain of promoter activity in the Compact mutant leads to a short internode phenotype in soybean through altered metabolism of gibberellin precursors. These results provide an example of how structural variation can control an important crop trait and a role for Glyma.17g145200 in soybean architecture, with potential implications for increasing crop yield.

Al Incorporation up to 99% in Metalorganic Chemical Vapor Deposition‐Grown Monoclinic (AlxGa1–x)2O3 Films Using Trimethylgallium

Growths of monoclinic (AlxGa1−x)2O3 thin films up to 99% Al contents are demonstrated via metalorganic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa) as the Ga precursor. The utilization of TMGa, rather than triethylgallium, enables a significant improvement of the growth rates (>2.5 μm h−1) of β‐(AlxGa1−x)2O3 thin films on (010), (100), and (01) β‐Ga2O3 substrates. By systematically tuning the precursor molar flow rates, growth of coherently strained phase pure β‐(AlxGa1−x)2O3 films is demonstrated by comprehensive material characterizations via high‐resolution X‐ray diffraction (XRD) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging. Monoclinic (AlxGa1−x)2O3 films with Al contents up to 99, 29, and 16% are achieved on (100), (010), and (01) β‐Ga2O3 substrates, respectively. Beyond 29% of Al incorporation, the (010) (AlxGa1−x)2O3 films exhibit β‐ to γ‐phase segregation. β‐(AlxGa1−x)2O3 films grown on (01) β‐Ga2O3 show local segregation of Al along (100) plane. Record‐high Al incorporations up to 99% in monoclinic (AlxGa1−x)2O3 grown on (100) Ga2O3 are confirmed from XRD, STEM, electron nanodiffraction, and X‐ray photoelectron spectroscopy measurements. These results indicate great promises of MOCVD development of β‐(AlxGa1−x)2O3 films and heterostructures with high Al content and growth rates using TMGa for next‐generation high‐power and high‐frequency electronic devices.

The role of carbon and C-H neutralization in MOCVD β-Ga2O3 using TMGa as precursor

In this Letter, the role of background carbon in metalorganic chemical vapor deposition (MOCVD) β-Ga2O3 growth using trimethylgallium (TMGa) as the Ga precursor was investigated. The quantitative C and H incorporations in MOCVD β-Ga2O3 thin films grown at different growth rates and temperatures were measured via quantitative secondary ion mass spectroscopy (SIMS). The SIMS results revealed both [C] and [H] increase as the TMGa molar flow rate/growth rate increases or growth temperature decreases. The intentional Si incorporation in MOCVD β-Ga2O3 thin films decreases as the growth rate increases or the growth temperature decreases. For films grown at relatively fast growth rates (GRs) (TMGa > 58 μmol/min, GR > 2.8 μm/h) or relatively low temperature (<950 °C), the [C] increases faster than that of the [H]. The experimental results from this study demonstrate the previously predicted theory—H can effectively passivate the compensation effect of C in n-type β-Ga2O3. The extracted net doping concentration from quantitative SIMS {[Si]-([C]-[H])} agrees well with the free carrier concentration measured from Hall measurement. The revealing of the role of C compensation in MOCVD β-Ga2O3 and the effect of H incorporation will provide guidance on designing material synthesis for targeted device applications.

Comparison of triethylgallium and diethylgallium ethoxide for β-Ga2O3 growth by metalorganic vapor phase epitaxy

The suitability of diethylgallium ethoxide (Et2GaOEt) containing Ga–O bonds as a Ga precursor for beta-gallium oxide (β-Ga2O3) growth by metalorganic vapor phase epitaxy (MOVPE) was investigated. Because estimating the growth behavior by thermodynamic analysis is difficult as a result of a lack of knowledge about the thermodynamics of Et2GaOEt, the growth behavior was estimated by observing its pyrolysis and combustion processes. Mass spectrometric analysis of gases sampled directly from an MOVPE reactor when only Et2GaOEt was supplied revealed that Et2GaOEt was decomposed to gallane, ethylene, and acetaldehyde by β-hydrogen (β-H) elimination at temperatures greater than 450 °C. However, when Et2GaOEt was supplied together with O2 to the MOVPE reactor maintained at 1000 °C, the combustion of hydrogen and carbon derived from Et2GaOEt was accelerated as the O2 supply was increased. In addition, the amount of O2 required for the complete combustion of Et2GaOEt (i.e., the amount required for the growth of β-Ga2O3) was clarified. On the basis of this pyrolysis/combustion behavior, homoepitaxial growth of β-Ga2O3 layers on β-Ga2O3 substrates was investigated at 1000 °C using Et2GaOEt as a Ga precursor and the growth behavior was compared with that when triethylgallium (Et3Ga) was used as a Ga precursor. Because both Ga precursors ultimately provide Ga gas after β-H elimination, no substantial difference in the growth rate was observed with respect to the amount of Ga atoms injected into the growth reactor. In addition, no substantial difference in crystallinity was observed; homoepitaxial layers grown at 0.7—0.8 μm/h were single crystals without twins, whereas those at 1.5—1.6 μm/h had twins. Et2GaOEt was found to be suitable as a Ga precursor for MOVPE of β-Ga2O3, with performance comparable to that of Et3Ga.

Rice OsGA2ox9 regulates seed GA metabolism and dormancy.

Rice OsGA2ox9 regulates seed GA metabolism and dormancy.

NODULE INCEPTION: a direct regulator of gibberellin biosynthesis during symbiotic nodulation.

This article is a Commentary on Gao et al. (2023), 239: 459–465.

Investigation of growth dynamics of β-Ga2O3 LPCVD by independently controlling Ga precursor and substrate temperature

We present results on low-pressure chemical vapor deposition (LPCVD) of β-Ga2O3 on a c-sapphire substrate with independent control of Ga precursor (T P) and substrate (T SUB) temperatures, allowing independent tuning of the Ga flux and thermal energy of the adatoms on the substrate surface. Experiments with constant T P = 900 °C with varying T SUB (600 °C–1050 °C) and varying T P (800 °C–1000 °C) with constant T SUB = 900 °C are reported. Island/nanorod formation on top of β-Ga2O3 thin film was observed at T SUB = 600–750 °C, suggesting the Stranski–Krastanov mode of growth, while thin film growth was observed for T SUB = 825–1050 °C. The growth rate decreased at higher T SUB, whereas it increased sharply for T P = 800–850 °C followed by a quasi-saturation for T P = 800–1000 °C. The growth rate evolution in both experiments reveals the significant role of gallium suboxide formation and desorption at the precursor/film during β-Ga2O3 LPCVD. This study provides useful insights into the growth dynamics involved in LPCVD of β-Ga2O3.

Self-catalyzed GaP nanowire MOVPE growth on Si

Typically, vapour liquid solid (VLS)-grown nanowires via metal–organic vapour phase epitaxy (MOVPE) use gold as a liquid growth catalyst. However, incorporating gold as an impurity during growth is disadvantageous. Therefore, we introduce the self-catalyzed VLS growth of GaP nanowires on Si (111) substrates via MOVPE, utilizing (deposited) Ga droplets as seed particles. To understand and optimize the growth process, the influence of various growth parameters such as Ga precursor preflow, growth temperature, growth time and V/III ratio are studied. As main findings we show that nanowire growth without strong tapering is possible. By varying the V/III gas phase ratio the tapering of nanowires can be manipulated during growth via droplet consumption. In addition, nanowires with lengths up to 10 µm and an aspect ratio of around 20 are demonstrated, showing only slight tapering. High-resolution scanning transmission electron microscopy measurements prove the zincblende crystal structure of the GaP nanowires in horizontal and vertical ultramicrotomy cuts. In vertical cross sections, a high number of microtwin boundaries perpendicular to the growth direction are found.

Structure and Thermal Stability of ε/κ-Ga2O3 Films Deposited by Liquid-Injection MOCVD.

We report on crystal structure and thermal stability of epitaxial ε/κ-Ga2O3 thin films grown by liquid-injection metal-organic chemical vapor deposition (LI-MOCVD). Si-doped Ga2O3 films with a thickness of 120 nm and root mean square surface roughness of ~1 nm were grown using gallium-tetramethylheptanedionate (Ga(thd)3) and tetraethyl orthosilicate (TEOS) as Ga and Si precursor, respectively, on c-plane sapphire substrates at 600 °C. In particular, the possibility to discriminate between ε and κ-phase Ga2O3 using X-ray diffraction (XRD) φ-scan analysis or electron diffraction analysis using conventional TEM was investigated. It is shown that the hexagonal ε-phase can be unambiguously identified by XRD or TEM only in the case that the orthorhombic κ-phase is completely suppressed. Additionally, thermal stability of prepared ε/κ-Ga2O3 films was studied by in situ and ex situ XRD analysis and atomic force microscopy. The films were found to preserve their crystal structure at temperatures as high as 1100 °C for 5 min or annealing at 900 °C for 10 min in vacuum ambient (<1 mBar). Prolonged annealing at these temperatures led to partial transformation to β-phase Ga2O3 and possible amorphization of the films.

Numerical Modelling for the Experimental Improvement of Growth Uniformity in a Halide Vapor Phase Epitaxy Reactor for Manufacturing β-Ga2O3 Layers

The development of growth processes for the synthesis of high-quality epitaxial layers is one of the requirements for utilizing the ultrawide band gap semiconductor Ga2O3 for high-voltage, high-power electronics. A halide vapor phase epitaxy (HVPE) process used to grow β-Ga2O3 layer was optimized by modifying the gas inlet, resulting in improved growth uniformity. A conventional tube acting as an inlet for the Ga precursor GaCl gas was replaced with a shower head with four outlets at 45 degrees to the horizontal axis of the reactor. The modification was performed based on numerical calculations of the three-dimensional distribution of gases inside the growth chamber with different designs of the GaCl precursor inlet. It was shown that variation in the Ga/O ratio over the substrate holder was ~10% for a shower head compared with ~40% for a tube. In addition, growth with a tube leads to the film thickness varying by a factor of ~4 depending on the position on the holder, whereas when using a shower head, the thickness of the grown Ga2O3 layers became much more uniform with a total spread of just ~30% over the entire substrate holder.

Carbon and silicon background impurity control in undoped GaN layers grown with trimethylgallium and triethylgallium via metalorganic chemical vapor deposition

The unintentional impurity incorporation in GaN epitaxial layers impacts the electrical conductivity and optical properties of the films grown by metalorganic chemical vapor deposition (MOCVD). It is critical to control impurity-related states for device structure development. The aim of this work is to contribute to the understanding of the reasons for the presence of certain background impurities. In this paper, the unintentional impurity incorporation of carbon, hydrogen, oxygen, and silicon in undoped (u-) GaN films grown by low-pressure MOCVD were studied. Background impurity concentrations were evaluated by secondary ion mass spectroscopy (SIMS) to optimize growth parameters including V/III ratio, growth temperature (Tg), growth pressure (Pg), and gallium (Ga) precursors of trimethylgallium (TMG) or triethylgallium (TEG). Unintentional [C] and [Si] incorporations are found to be highly dependent on the growth parameters. For the same growth conditions, u-GaN films grown with a TEG precursor exhibited a lower background concentration of C compared to that of GaN grown with TMG. However, the lowest background [C] achieved was grown with TMG using optimized conditions and exhibited [C] < 4 × 1015 cm−3 which was at the detection limit of the SIMS measurement. These results were measured for a u-GaN layer grown with TMG at 200 Torr, 1030 °C, and a V/III of 3700. The lowest background [Si] of 4 × 1015 cm−3 was achieved by growing with TMG at 200 Torr, 1000 °C, and V/III of 650.