H2 Carrier Gas Research Articles

High Performance CMOS RF Switch Based on Highly Carbon Doped Raised Source/Drain Regions

The demand for high-performance Radio Frequency (RF) CMOS RF SOI (Silicon on Insulator) switches has rapidly increased, driven by the need for advanced wireless technologies (1). In this paper we give new insights on high carbon incorporation, where a Si(1-y)Cy layer with 1% of substitutional carbon (y = Csub) is grown on 40 nm on top on silicon. This layer is used for Raised Source/Drain (RSD) to strain the Si channel, for reducing on-state resistivity (Ron) and which should result in a theoretical 16% gain in current (3), (4). Si(1-y)Cy growth parameters were carefully optimized to increase Csub. Firstly, with the reduction of the temperature. Then, with H2 carrier gas reduction and total pressure increase. These two process modifications have a positive impact on the carbon concentration, thanks to the higher growth rate, without layer relaxation (5).

Biomass gasification tar removal using dielectric barrier discharge reactor: Effect of reactor geometry and carrier gases

This study investigates the impact of reactor geometry (varying external electrode length) of Dielectric Barrier Discharge (DBD) reactors on the decomposition of toluene, a model compound for biomass gasification tar, using different carrier gases and various power levels. Results reveal that toluene decomposition is higher at longer electrode lengths (30 mm) at all power levels tested. Specifically, the toluene decomposition in H2 carrier gas at 30 mm electrode length increased from 67.2 % to 97.5 % with rising power from 5 to 40 W, while it ranged from 52 % to 97.4 % at 15 mm electrode length. The decomposition of toluene was found to be higher in N2 carrier gas than in H2 carrier gas at both discharge lengths. At 30 mm external electrode and with rising power from 5 to 40 W, toluene decomposition ranged from 90.5 % to 98.7 %. Similarly, when the electrode length was reduced from 30 to 15 mm for N2 carrier gas, the decomposition of toluene ranged from 74 % to 97.9 %. Thus, the results indicate that the decomposition of toluene is affected by both the electrode length and the nature of the carrier gas. The effect of electrode length was significant at lower power levels, and the difference between the conversion at both electrode lengths nearly disappeared at higher power levels.

Investigation of Hydrogen Flux Influence on InGaP Layer and Device Uniformity

In this study, we conduct a comprehensive examination of the influence of hydrogen (H2) carrier gas flux on the uniformity of epitaxial layers, specifically focusing on the InGaP single layer and the full structure of the InGaP/GaAs heterojunction bipolar transistor (HBT). The results show that an elevated flux of H2 carrier gas markedly facilitates the stabilization of layer uniformity. Optimal uniformity in epitaxial wafers is achievable at a suitable carrier gas flux. Furthermore, this study reveals a significant correlation between the uniformity of the InGaP single layer and the overall uniformity of HBT structures, indicating a consequential interdependence.

Direct growth of highly oriented GaN thin films on silicon by remote plasma CVD

We report on low-temperature (500 °C) and low-pressure (0.3 mbar) direct growth of GaN thin films on silicon (100) substrates using remote plasma chemical vapour deposition (RP-CVD). In the custom-designed reactor, an RF inductively coupled plasma is generated remotely from the substrate’s area to facilitate the decomposition of group-V precursor, N2 with added H2, while group-III precursor trimethylgallium (TMGa), is directly injected into the growth chamber mixed with H2 carrier gas. Growth parameters such as RF power, process pressure and gas flow rates have been optimized to achieve a film growth rate of about 0.6 µm h−1. Several characterization techniques were used to investigate the plasma and the properties of the grown thin films in terms of their crystallinity, morphology, topography, and composition. The films are highly textured with a preferential orientation along the c-axis of the wurtzite structure. They present a small roughness in the nanometer range and a columnar microstructure with a grain size of one hundred nanometer, and a gallium polarity (+c plane oriented). Rutherford backscattering spectrometry and nuclear reaction analysis show that the chemical composition is homogeneous through the depth of the layer, with a III/V ratio close to 1, a very low content of oxygen (below the detection limit ∼1%) and a carbon content up to 11%. It was shown that the increase of plasma power helps to reduce this carbon contamination down to 8%. This research paves the way for a growth method compatible with cost reduction of III–V thin film production achieved through reduced gas consumption facilitated by RP-CVD operation at low pressure.

Modeling hydrodynamic and biomass pyrolysis effects of recycled product gases in a bubbling fluidized bed reactor

Fast pyrolysis of biomass in a fluidized bed reactor is typically conducted in a nitrogen gas environment. Recycling product gas can improve the economics of operating such a system by reducing reliance on pure process streams, but much less is known about how recycling pyrolysis product gas may affect fluidization behavior and pyrolysis kinetics. Therefore, gas effects in a fluidized bed biomass pyrolysis reactor were investigated using engineering correlations, low-order models, and CFD simulations for N2, H2, CO, CO2, and CH4 carrier gas mixtures. Our findings reveal viscosity of a gas mixture can be significantly underestimated depending on the model and correlation. Furthermore, fluidization characteristics such as Umf and gas-solid convective heat transfer can be greatly affected by the gas properties. By utilizing H2 as the fluidizing gas (instead of N2), while maintaining a constant fluidization ratio (Us/Umf), the bio-oil yields can be increased ∼5%. This is due to the lower density H2 producing similar hydrodynamics as N2 at higher gas flow rates. These higher flow rates result in shorter gas residence times, and as a result, less secondary reactions that convert bio-oil to light gases and char. Model results also suggest that bio-oil yield is not significantly affected by the type of carrier gas used, with bio-oil yield varying by ∼2% across different gas mixtures while maintaining constant flow rate. This indicates that recycled pyrolytic gas can be used as the carrier gas for biomass pyrolysis.

Low-Leakage Current Core-Shell AlGaN Nanorod LED Device Operating in the Ultraviolet-B Band.

Despite the considerable potential of AlGaN-based ultraviolet-B light-emitting diodes (UV-B LEDs) in various applications such as phototherapy, UV curing, plant growth, and analytical technology, their development is still ongoing due to low luminescence efficiency. In this study, we introduced a novel epitaxial growth mechanism to effectively control the height and thickness of AlGaN multiple wells (MWs) on AlGaN nanorod structures using horizontal reactor-based metal-organic chemical vapor deposition (MOCVD). By adjusting the H2 carrier gas flow rate, we could control the growth boundary layer's thickness, successfully separating the AlGaN well and p-AlGaN layer from the substrate. Cathodoluminescence (CL) measurements confirmed the stability of the core-shell AlGaN quantum wells as a highly stable nonpolarized structure, with the wavelength peak remaining almost unchanged under various injection currents. Furthermore, transmission electron microscopy (TEM) provided clear evidence of differentiation, highlighting the distinct formation of the 275 nm AlGaN core and the 295 nm AlGaN shell structure. The developed AlGaN MW structure, characterized by these rectification features, not only demonstrated a significantly improved electroluminescence (EL) peak intensity but also exhibited a much lower leakage current compared to the conventional core-shell AlGaN structure. The newly proposed growth mechanism and advanced nonpolarized core-shell AlGaN structure are expected to serve as excellent alternatives for substantially enhancing the efficiency of the next generation of high-efficiency UV LEDs.

MOCVD Growth of Tungsten Ditelluride Thin Films

The growth of tungsten ditelluride (WTe2) thin films on c-plane sapphire substrates was demonstrated by metalorganic chemical vapor deposition (MOCVD) using tungsten hexacarbonyl (W(CO)6) and diethyltelluride (DETe) as precursors for W and Te, respectively, in a H2 carrier gas. The effects of substrate temperature, reactor pressure, precursor and carrier gas flow rates, and chalcogen-to-metal ratio on the WTe2 growth rate and film properties were determined. Substrate temperatures less than 500 °C were required to deposit WTe2 which was found to be beneficial to suppress simultaneous carbon deposition from the DETe precursor. The films exhibited a fine-grained morphology independent of growth temperature. The layered crystalline 1 T’ phase of WTe2 was confirmed using high resolution X-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (TEM) which revealed that the films were predominantly c-axis oriented with in-plane twist. X-ray photoelectron spectroscopy (XPS) demonstrated that the WTe2 films were stable in air for a few days but eventually exhibited oxidation.

A Rapid Derivatization for Quantitation of Perfluorinated Carboxylic Acids from Aqueous Matrices by Gas Chromatography-Mass Spectrometry.

Ultrashort-chain perfluorinated carboxylic acids (PFCAs) are receiving more attention due to their ever-increasing presence in the environment. Methods have been established for the analysis of short- and long-chain PFCAs, while robust quantitation of ultrashort-chain species is scarce. Here, we develop a novel derivatization method using diphenyl diazomethane for quantitation of C2-C14 PFCAs in aqueous matrices. The method is highlighted by rapid completion of derivatization (<1 min) and retention and separation of ultrashort-chain (C2/C3) PFCA derivatives using H2 carrier gas (R > 1.5). A weak anion exchange solid-phase extraction procedure for analyte recovery from representative aqueous samples was developed and validated by spike and recovery from ultrapure water, synthetic ocean water, and simulated denuder extracts used for collecting gaseous PFCAs. Recoveries for PFCAs ranged from 83 to 130% for the majority of analytes and matrices. The instrument detection limits (IDLs) range from 8 to 220 fg per injection, and method detection limits (MDLs) range from 0.06 to 14.6 pg/mL for 500 mL aqueous samples, which are within an order of magnitude to conventional LC-MS/MS methods. The method was applied to the analysis of real samples of tap water, rainwater, ocean water, and annular denuder extracts. The overall method provides a cost-effective alternative to conventional LC-MS/MS methods, overcoming the typical GC-MS drawbacks of high detection limits and long sample preparation times while being able to simultaneously analyze the complete spectrum of environmentally relevant PFCAs.

Ethanol Coupling Reactions over MgO-Al2O3 Mixed Oxide-Based Catalysts for Producing Biofuel Additives.

Catalytic conversion of ethanol to 1-butanol was studied over MgO-Al2O3 mixed oxide-based catalysts. Relationships between acid-base and catalytic properties and the effect of active metal on the hydrogen transfer reaction steps were investigated. The acid-base properties were studied by temperature-programmed desorption of CO2 and NH3 and by the FT-IR spectroscopic examination of adsorbed pyridine. Dispersion of the metal promoter (Pd, Pt, Ru, Ni) was determined by CO pulse chemisorption. The ethanol coupling reaction was studied using a flow-through microreactor system, He or H2 carrier gas, WHSV = 1 gEtOH·gcat.-1·h-1, at 21 bar, and 200-350 °C. Formation and transformation of surface species under catalytic conditions were studied by DRIFT spectroscopy. The highest butanol selectivity and yield was observed when the MgO-Al2O3 catalyst contained a relatively high amount of strong-base and medium-strong Lewis acid sites. The presence of metal improved the activity both in He and H2; however, the butanol selectivity significantly decreased at temperatures ≥ 300 °C due to acceleration of undesired side reactions. DRIFT spectroscopic results showed that the active metal promoted H-transfer from H2 over the narrow temperature range of 200-250 °C, where the equilibrium allowed significant concentrations of both dehydrogenated and hydrogenated products.

Effect of in-situ SiNx grown with different carrier gas on structural and electrical properties of GaN-based MISHEMTs

In this work, the effect of in situ SiNx grown with different carrier gas on the structural and electrical properties of the SiNx/AlGaN/GaN MIS-HEMTs is studied. It was found that the growth rate of SiNx grown with N2 as carrier gas (N2-SiNx) is more sensitive to different growth conditions, while the growth rate of SiNx grown with H2 as carrier gas (H2-SiNx) is very stable due to the inhibiting effects of H2 carrier gas on the SiH4–NH3 forward reactions. More importantly, a continuous and smooth SiNx growth at the initial stage can be realized with H2 carrier gas due to its faster surface migration, leading to a decent surface morphology and sharp interface of H2-SiNx. As a result, the SiNx passivated device with H2 as carrier gas shows improved performance compared to that with N2 as carrier gas, featuring ultra-low interface-state density of 2.8 × 1010 cm−2 eV−1, improved on- and off-state current, reduced threshold voltage shift, and mitigated current collapse, especially after long-term electrical stress. These results not only elaborate on the growth mechanisms of in situ SiNx with different carrier gases but also highlight the advances of H2 as carrier gas for in situ SiNx growth, providing an effective strategy to tailor the passivation schemes for GaN-based devices.

Very Low Temperature Tensile and Selective Si:P Epitaxy for Advanced CMOS Devices

Nowadays, “more Moore” and “more than Moore” device architectures are becoming more and more complex. In CEA-Leti, we work on the “CoolCubeTM” 3D sequential integration which is based on the stacking of FDSOI devices [1]. We present solutions, at T<500°C, for the integration of SiP Raised Sources & Drains (RSD) in the upper devices without degrading the electrical performances of the bottom ones. We also target a lowering of the RSD resistance and an increase of the electron mobility in the channel of NMOS devices thanks to tensile strain [2]. Such a know-how will be useful to minimize the contact resistance and fabricate other types of devices such as FINFETs or h-GAA (e.g. nano-sheet devices) with Si (110) surfaces.Experiments were carried out in an Applied Materials epitaxy reactor featuring (i) liquid precursor delivery, together with H2, N2 or He carrier gas capability, enabling the use of Cl2; (ii) “High Precision Temperature Control (HPTC)”, allowing excellent LT control and enabling flexible rotation speeds; (iii) “precision flow distribution PFD-III”, enhancing uniformity performances. Selective Epitaxial Growth (SEG) is usually obtained with “co-flow” processes at rather high temperatures (>600°C). Chlorinated precursors (SiH2Cl2 (+ GeH4) + HCl, typically) are then sent simultaneously into the growth chamber. At LT (<500C°C), HCl cannot decompose, however. To overcome those limitations, we used a Cyclic Deposition Etch (CDE) strategy, with non-selective depositions followed by selective chemical vapor etches, to obtain SiP SEG.This strategy allowed us to obtain high quality films, as shown in Fig.1. The Omega-2Theta scans around the (004) X-Ray Diffraction order for tensile SiP (t-SiP) layers grown at T < 500°C with different Phosphorus concentrations were indeed typical of monocrystalline layers, with well-defined and intense peaks together with numerous thickness fringes. The substitutional P contents in those ~ 60 nm thick t-SiP layers were in the 1.02% - 5.42% range. The good layer uniformity in terms of thickness and P content, over a 300mm wafer radius, is shown in figure Fig.2.These layers grown at T <500°C were smooth, as shown in Fig.3, with a 0.21 nm Root Mean Square (RMS) roughness for a 60nm thick Si:P layer, i.e. a value close to the typical RMS roughness for t-SiP layers grown at high temperature with a chlorinated chemistry.The electrical resistivity in various t-SiP layers is plotted in Fig.4 as function of the substitutional phosphorus concentration and for various growth temperatures in the 450°C – 525°C range. Reducing the temperature by 75°C halved the electrical resistivity. We were able to achieve a resistivity as low as 0.21 mOhm.cm for a t-SiP layer with 5.8% of P grown at 450°C.We then evaluated, at first on tests structures without gates, our process selectivity. A top view Scanning Electron Microscopy image of a t-SiP layer grown non-selectively, with numerous amorphous SiP nuclei on SiO2, is shown in Fig 5.a. After some careful optimization, we succeeded in having fully selective processes versus SiO2, as shown in Fig 5.b.We then tested such optimized processes on low density FD-SOI devices with 28 nm design rules. A top-view SEM image of transistors after such a growth is shown in Fig.6. The growth selectivity was excellent, with nitride spacers and hard masks as well as isolations free of a-SiP nuclei for 31 nm of t-SiP with 4.5% of P deposited in the Sources/Drains. The surface was smooth, with a RMS roughness as low as 0.30nm on active areas, as shown in Fig.7. Thanks to High Resolution Reciprocal Space Maps (HR-RSM), we measured a Phosphorus concentration of 4.5% for that SiP layer grown on SOI. The very high quality of that epitaxy layer, with well-defined thickness fringes, is obvious in Fig.8. Cross-sectional Transmission Electron Microscopy (TEM) images such as the one shown in Fig. 9 enabled us to confirm, at the nanoscale, the excellent quality of such layers in RSDs.To sum up, we were able to develop a tensile Si:P process which was shown to be selective, at a temperature lower than 500°C, against SiO2 and SiN. Such t-SiP layers were successfully integrated in the Sources/Drains regions of FD-SOI 28nm devices. The very low material resistivity and the high phosphorus content should yield, notably because of tensile strain, performant NMOS devices in the near future.[1] C. Fenouillet-Beranger et al., IEEE TED 68, 3142-3148 (2021)[2] V. Chan et al., IEEE 2005 Custom Integrated Circuits Conference 2005, pp. 667-674 Figure 1

Ultra-low resistance n+GaN contacts for GaN HEMT applications using MOCVD selective area epitaxy in N2 carrier gas

Low resistance n+GaN contact materials were experimentally studied for GaN HEMT applications by selective area epitaxy regrowth on a patterned SiC substrate. Epitaxy was performed by metal organic chemical vapor deposition using 100% H2 or 100% N2 as the carrier gas. Thin film characterization demonstrated that n+GaN grown in N2 carrier gas has a superior morphology with improved crystalline quality to that grown in H2 carrier gas. The results also indicated that the surface morphology of n+GaN grown in N2 carrier gas is less sensitive to mask pattern density and micro-loading effects with Si doping concentrations up to 1 × 1020/cm3. Secondary ion mass spectrometry analysis shows that C and O impurity levels in n+GaN are one order of magnitude lower with N2 carrier gas than with H2. The electrical measurement of transmission line model structures shows an n+GaN sheet resistance of 15 Ω/sq and an Ohmic metal to n+GaN contact resistance of 0.02 Ω-mm for structures grown in N2 carrier gas. These values represent 7.1× and 2.5× improvements compared to H2 carrier gas.

Analytical artefacts: H2 carrier gas hydrogenation of plant volatiles during headspace solid-phase microextraction gas chromatography.

Hydrogen is the most efficient and economical carrier gas for gas chromatography (GC). However, there are rare reports of artefact formation by hydrogenation of unsaturated compounds on GC. Head space solid-phase microextraction (HS-SPME) GC conditions for hydrogenation were studied. HS-SPME-GC-mass spectrometry (MS) analyses of common classes of plant volatiles were carried out using hydrogen (H2 ) and helium (He) carrier gases with different SPME fibre coatings, GC inlet temperatures, and desorption times. Common phenylpropanoids, monoterpenes, and green leaf volatiles were hydrogenated to varying degrees on HS-SPME-GC with H2 carrier gas and SPME fibres coated with polydimethylsiloxane (PDMS)/Carboxen (CAR), PDMS/divinylbenzene (DVB), and PDMS/CAR/DVB. No artefacts were detected using PDMS-only coated fibres or He carrier gas. Unsaturated plant volatiles may be hydrogenated on HS-SPME-GC when using H2 carrier gas with SPME fibre coatings containing DVB polymer or CAR porous particles. Parallel analyses with He and H2 carrier gases are recommended when developing HS-SPME-GC methods for plant volatiles, or use of PDMS-only coated fibres.

(Invited) Unidirectional Epitaxy of TMD Monolayers on Sapphire

Wafer-scale synthesis of semiconducting transition metal dichalcogenide (TMDs) monolayers is of significant interest for device applications to circumvent size limitations associated with the use of exfoliated flakes. Promising results have been demonstrated for epitaxial films deposited by vapor phase techniques such as CVD and MOCVD. However, the three-fold symmetry of TMDs such as MoS2 and WSe2, results in two energetically equivalent domain alignments, often referred to as 0o and 60o domains, when grown on substrates such as c-plane sapphire and graphene. The oppositely oriented domains give rise to inversion domain boundaries (IDBs) upon coalescence which exhibit a metallic character and are generally undesirable. In this study, we demonstrate the epitaxial growth of unidirectional TMD monolayers on 2” diameter c-plane sapphire substrates with a significantly reduced density of inversion domains. Steps on the sapphire surface are shown to break the surface symmetry giving rise to a preferred domain orientation.Metalorganic chemical vapor deposition (MOCVD) was used for the epitaxial growth of WSe2 and WS2 monolayers on c-plane sapphire in a cold-wall horizontal quartz-tube reactor. The as-received sapphire substrates, which are miscut ~0.2o toward <112 ̅0>, consist of steps with sub-1 nm step height separated by 50-70 nm wide terraces. A three-step nucleation-ripening-lateral growth process, carried out at temperatures ranging from 850oC to 1000oC, was used to achieve epitaxial films using W(CO)6, H2Se and H2S as precursors in a H2 carrier gas. Nucleation was observed to occur at the terrace edge and the growing domains align epitaxially with the underlying (0001) sapphire lattice. As a result of the nucleation process, the domains grow with a zig-zag edge facing the terrace edge which imparts a preferential direction to the domains. The percentage of domains with a preferred direction ranges from 75%-86% depending on MOCVD growth conditions. Continued lateral growth for times ranging from 10-30 minutes results in fully coalesced TMD monolayers that are epitaxially oriented on the sapphire, as assessed by in-plane x-ray diffraction, with a reduced density of inversion domain boundaries. The results demonstrate the important role of surface structure in nucleation and epitaxial growth of TMD monolayers.

A comparison of the decomposition of biomass gasification tar compound in CO, CO2, H2 and N2 carrier gases using non-thermal plasma

In this study, a comparative decomposition of toluene was investigated using a dielectric barrier discharge (DBD) reactor. The first-time decomposition of the tar model compound was investigated in pure CO gas. The effect of each carrier gas (N2, H2, CO2 and CO), which exists in product gas from the gasifier, was studied on the decomposition of tar analogue (toluene) and product distribution. The specific input energy (SIE) was also varied from 2.5 to 8.5 kJ/L to investigate the optimal removal of tar analogue. The maximum removal of toluene was 89.1% using N2 as carrier gas at 8.5 kJ/L and 1.43 s. However, the minimum removal of toluene was 62.5% using CO carrier gas under the same conditions. The decomposition of toluene in different carrier gases was in the following order: CO < CO2 < H2 < N2. Moreover, the distribution of products depends on the nature of the carrier gas as well. However, lower hydrocarbons (LHC) (<C7) and solid residues were observed in each carrier gas. The maximum yield of LHC was about 10.8% in H2 carrier gas, whereas in CO and CO2 it remained below 1% even at 8.5 kJ/L.

Study of silicon nitride deposition in III-N MOVPE reactors

Si3N4 deposition from silane and ammonia in a number of III-N MOVPE reactors of various sizes was studied in a wide range of reactor conditions. It was revealed that Si3N4 deposition rate depends on temperature, pressure, carrier gas type, and ammonia concentration. Deposition rate rises with temperature up to 1050–1100 °C in a manner typical for temperature-activated processes, but under any studied conditions, including the 800–850 °C range, it is strictly linear with SiH4 concentration indicating the absence of high-order parasitic reactions at high temperature and surface passivation at low temperature. For a low-volume reactor the higher the pressure is, the faster the deposition is both for N2 and H2 carrier gases. For large reactors the dependence is non-monotonic. At temperature above 900 °C using H2 as a carrier gas results in a higher Si3N4 deposition rate than when using N2. If nitrogen is used as a carrier gas, deposition rate gradually rises with ammonia concentration. If hydrogen is used, deposition rate rapidly rises with ammonia concentration and then gradually falls. If hydrogen-nitrogen mixture is used as a carrier gas, deposition rate changes in a linear manner with the mole fraction of hydrogen in the carrier gas.

Morphological Control of Silicon Carbide Deposited on Hi-Nicalon Type S Fiber Using Atmospheric Pressure Chemical Vapor Infiltration.

Silicon carbide coated onto Hi-Nicalon Type S fiber is of great interest to the aerospace industry. This work focuses on tuning the reaction parameters of atmospheric pressure SiC CVI using CH3SiCl3 to control the morphology of the coatings produced. Depth of CH3SiCl3 from 1 to 14 cm, temperature from 1000 to 1100 °C, and flow rate of H2 carrier gas from 5 to 30 SCCM were examined. Coating morphologies ranged from smooth to very nodular, where spherical growths were present along the entire deposition zone. The parameters that yielded a smooth deposition throughout the 20 cm deposition zone were 4–6 cm of CH3SiCl3(l) depth, 1100 °C, and 10 SCCM of H2 as a carrier gas. Tensile testing using acoustic emission sensors was performed on SiCf/BN/CVI-SiC minicomposites with different coating morphologies. The tensile tests revealed that smooth coatings have better mechanical performance than the nodular coatings; nodular coatings promote premature ultimate brittle failure, while smooth coatings exhibit toughening mechanisms. Smooth coatings had higher average matrix cracking strength (248 MPa) and ultimate tensile strength (541 MPa) than average nodular coating matrix cracking strength (147 MPa) and ultimate strength (226 MPa).

Fast-filling of 4H-SiC trenches at 10 μm/h by enhancing partial pressures of source species in chemical vapor deposition processes

4H-SiC trenches with depths of approximately 25 μm were filled under a special condition called the quasi-selective epitaxial growth mode that showed a refill-rate of 2.1 μm/h within 12 h, using a hot-wall chemical vapor deposition (CVD) method with the assistance of HCl gas. To develop a high-rate growth mode for the 4H-SiC trench filling process, several CVD growth parameters, such as the flow rates of source gases, HCl and H2 carrier gases, their pressures, and the applied C/Si ratio, were regulated and optimized, to enhance the partial pressures of the source species in the gas phase of the CVD reactor. A refill-rate of 11.4 μm/h in 2 h was achieved, which is nearly five times faster than the initial growth.

Roles of growth kinetics on GaN non-planar facets under metalorganic vapor phase epitaxy condition

The behavior of Ga adatom on GaN non-planar facets during metalorganic vapor phase epitaxy (MOVPE) is investigated on the basis of ab initio calculations. For non-planar facet consisting of and planes, we find that the Ga adatom is preferentially incorporated on planar surface region for H2 carrier gas whereas the migration of Ga adatom from non-planar facet to planar surface hardly occurs for N2 carrier gas. These results suggest that the difference in Ga adatom behavior is one of the origins for the aspect ratio difference of GaN nanostructures by carrier gas in the MOVPE.

Equilibrium Morphologies of Faceted GaN under the Metalorganic Vapor‐Phase Epitaxy Condition: Wulff Construction Using Absolute Surface Energies

An equilibrium Wulff construction using absolute surface energies for various orientations is conducted to elucidate the morphology change of GaN under the metalorganic vapor‐phase epitaxy (MOVPE) condition. The calculated equilibrium shapes suggest that the morphology mainly consists of and facets under Ga‐rich condition for selective area growth (SAG) on lateral direction. In contrast, an equilibrium crystal shape including the larger area of facets and (0001) plateau with smaller facets emerges under N‐rich condition. Furthermore, by incorporating growth conditions such as growth temperature and carrier gas, it is found that the (0001) plateau hardly emerges under H2 carrier gas condition at low temperature. The results under H2 carrier gas are found to be different from those under N2 carrier gas where the (0001) plateau slightly emerges at low temperature. The calculated results manifest that our approach can provide the determination of equilibrium shape of semiconductor materials during epitaxial growth.