We investigated the mechanism of metal-organic vapor phase epitaxy (MOVPE) growth for InGaN by comparing experimental and simulation results. The simulation results showed a similar trend to the experimental results. Therefore, the simulation system can be used to speculate on physical and chemical phenomena through the behavior of precursors. InGaN growth is largely affected by the amounts of both trimethylindium (TMIn) and NH3 supplied. This is because InN growth is dependent on the amount of NH2 physisorbed on a surface, which is generated by NH3. Moreover, the decomposition of crystallized InN and the desorption of these decomposed precursors of InN during growth cannot be ignored. (C) 2013 The Japan Society of Applied Physics

We investigated the state of the Si(111) surface and its effect on InAs growth after annealing at high temperature with and without an As or P source flow in H-2 ambient in metal-organic vapor phase epitaxy (MOVPE). In multi-step growth of InGaAs by micro-channel selective-area growth, perfect coverage of Si growth areas by InAs, which is grown first, by controlling the state of the Si surface is critical for the following InGaAs lateral growth. Although both As and P sources protect the surface against contamination from inside the reactor, annealing with the P source at high temperature is optimal in terms of InAs nucleation and coverage of growth areas by InAs. The amount of O contamination after P annealing at high temperature was significantly lower than that under other annealing conditions. Therefore, O is the most critical contamination in InAs nucleation. (C) 2011 The Japan Society of Applied Physics

We have successfully formed a thin twin-free layer on the top of InGaAs micro-discs by multi-step growth using micro-channel selective-area MOVPE on Si(1 1 1) substrates. The multi-step growth employs a gas flow sequence in which the partial pressure of the Ga source (trimethylgallium: TMGa) is modulated to control the initial nucleation and the direction of subsequent growth. We have previously improved in-plane uniformity of crystal shape of InGaAs micro-discs by 3-step growth that starts with InAs nucleation. Using these micro-discs as templates, InGaAs with tripled partial pressure of TMGa was grown as the fourth step. The growth of this fourth layer on the disc surface seems to suppress the layer-by-layer growth on the (1 1 1) plane and to terminate rotational twins, as well as keeping the size deviation of micro-discs under 25%. One of the most laterally grown micro-discs (with thickness of 380 nm and width of 7.1 mu m) had a 50-nm-thick twin-free layer on the top. (C) 2009 Elsevier B.V. All rights reserved.

We have obtained a dislocation-free InGaAs layer on Si(111) using micro-channel selective-area metalorganic vapor phase epitaxy. By increasing the supply of the Ga precursor, we removed rotational twins, which have been observed in III-V layers on (111) substrates. From analysis of the atomic structure, the Ga content in the crystal was found to increase gradually as the growth proceeded. This increase resulted in growth in a tilted direction from [111] and extinction of twins. It was concluded that a twin-free InGaAs layer can be obtained when a Ga-rich layer is inserted in the middle of the growth. (C) 2009 The Japan Society of Applied Physics

We investigated the dependence of the growth mode on the Ga content in micro-channel selective-area MOVPE of InGaAs on Si(111) substrates by changing the partial pressure of a Ga source. The Ga content in the crystal was affected by the initial nucleation and the shape of InGaAs islands after growth. In the growth of InAs, a single columnar nucleus was generated in each open window and a hexagonal column was eventually grown. The content of the initial nuclei of InGaAs were close to InAs. As the partial pressure of a Ga source was increased, the number of nuclei in a growth area increased, their shape became rounded, and a slight amount of Ga was incorporated into the nuclei. The InGaAs islands showed enhanced lateral growth as the partial pressure of a Ga source was increased and incoherent growth without specific crystallographic planes became apparent at a high Ga content. The InGaAs islands that grew in the lateral direction had an inhomogeneous Ga content with a higher Ga content at the peripheral region. It appears that incorporation of Ga suppresses coherent growth of In(Ga)As in the vertical direction and enhances lateral growth, although high Ga content can induce incoherent growth. (C) 2008 Elsevier B.V. All rights reserved.

Kinetic analysis of the surface adsorption layer on GaAs, InAs, InP, and GaP surfaces during metalorganic vapor phase epitaxy (MOVPE) was performed by in situ monitoring of the temporal behavior of surface reconstructions using reflectance anisotropy spectroscopy (RAS). When the flow of group-Ill sources was switched on/off, the transient RA signal exhibited two time constants to and t(1) in response to the generation/extinction of the adsorption layer. It was considered that t(0), when the supply of group-III sources was started, corresponds to the adsorption of group-III atoms from the gas phase to the adsorption layer, and that t(1), when the supply of group-Ill sources was terminated, is associated with the incorporation of adsorbed group-Ill atoms to the crystal. The rate constant of adsorption, I/t(0), was approximately 2(s-1) for all surfaces except for GaP. The rate constant of incorporation, 1/t(1), ranged from 0.1 to 10s(-1). It was found that 1/t(1) for the As-containing materials was faster than that for P-related materials, and 1/t(1) for In-containing materials was faster than that for the Ga-containing materials. For the As-containing materials, 1/t(1) agreed with the incorporation rate constants of adsorbed group-Ill precursors obtained using the Langmuir-Hinshelwood model by the analysis of selective-area growth (SAG). (C) 2008 Elsevier B.V. All rights reserved.

A kinetic analysis of the surface adsorption layer of III/V semiconductors in metalorganic vapor phase epitaxy (MOVPE) was carried out by monitoring the temporal behavior of surface reconstruction that is assumed to be maintained during growth with the adsorption layers. A GaAs(001) surface was observed in situ using reflectance anisotropy spectroscopy (RAS), and both spectroscopic and kinetic analyses were pet-formed when trimethylgallium (TMGa) was supplied intermittently while the supply of tertiarybutylarsine (TBAs) was continuous. When the flow of TMGa was switched on/off, the transient RA signal exhibited time constants of 0.2-20s. By observing the dependence of these time constants on the partial pressure of TMGa and substrate temperature, we considered that the time constant (to) at the start of TMGa supply corresponds to the adsorption of Ga from the gas phase to the adsorption layer, and two constants (i.e., t(1) and t(2)) at the end of TMGa supply are associated with the crystallization of adsorbed Ga and the recovery of surface reconstruction, respectively. The equivalent thickness of the adsorption layer was estimated to be 0.19 monolayer thickness at 550 degrees C.

Abstract

Fcc‐Ti_xAl_1–xN (TiAlN) coatings synthesized via chemical vapor deposition (CVD) reduce cutting tool wear. Although CVD conditions reportedly influence coating quality, no quantitative guidelines are yet available. To quantitatively study the film‐forming mechanism of TiAlN CVD, the gas composition over the surface must be known. Therefore, we developed a gas‐phase elementary reaction model for TiAlN CVD derived from TiCl₄/AlCl₃/NH₃. First, we constructed a novel thermodynamic dataset including molecules that contained both Ti and Al, and calculated the equilibrium composition. Thermal equilibrium calculations in the gas phase showed that the most stable species were AlCl₃ and TiCl₃ rather than TiCl₄. An elementary reaction model was constructed based on the kinetics of the gas‐phase species that were generated. Kinetic analysis revealed that gas‐phase reactions were largely absent under our reactor conditions. The thermal equilibrium calculations indicated that TiCl₄ may have given rise to TiCl₃. Thus, other reaction pathways of TiCl₄ to TiCl₃ were explored. We calculated the reaction rate constants of 12 reactions of Ti species and added them to the model, which revealed that TiCl₄ decomposed to TiCl₃ via TiCl₃NH₂. Under our conditions, TiCl₄ and TiCl₃NH₂ are the major Ti species and AlCl₃ and AlCl₂NH₂ are the major Al species, which suggests that some of these species may form films. Unlike in the earlier reaction model, NH₂ and H radicals were produced, which may have contributed to the surface reactions. For reactors with large Surface/Volume ratio of reactor, the effects of gas‐phase reactions should be considered. Our reaction model enables estimation of the partial pressures of reactor gas species and will therefore aid study of the TiAlN deposition mechanism.

It is highly challenging to grow high-quality gallium nitride (GaN) layers on silicon (Si) substrates due to the intrinsic mismatching of their structural and thermal properties. Aluminum nitride (AlN) interlayers have been used to induce a compressive strain to GaN layers during growth, which compensates for the tensile strain in these layers on Si substrates during cooling. In this study, we investigated the effect of the growth temperature and layer structure of the AlN interlayer to understand the relationship between surface flatness and relaxation ratio of the AlN interlayer and the compressive strain in the overlying GaN layer. Low-temperature (LT) growth enhanced lattice relaxation of the AlN interlayer, whereas the AlN surface was atomically flat at high temperature (HT). We also examined a two-step growth to combine the advantages of LT- and HT-AlN. This approach resulted in a surface with multiple flat regions separated by grooves, which had the largest compressive strain in the overlying GaN layer at the early stages of growth. At later stages, the strain was the largest on the HT-AlN interlayer. In both cases, the experimentally measured compressive strain exceeded simulated predictions. Finally, possible solutions for inducing a larger compressive strain in the GaN layer using interlayers were discussed.

ScAlMgO4 (SAM) has attracted attention as a substrate for nitride semiconductor crystal growth owing to its small a-axis lattice mismatch with GaN and InGaN. In this study, we investigated GaN growth on a SAM substrate via radio-frequency plasma-excited molecular beam epitaxy. By optimizing the growth conditions, GaN with the following epitaxial orientation relations (0001)GaN//(0001)SAM and [11-20]GaN//[11-20]SAM was successfully grown directly on the SAM substrate. The atomically flat and abrupt interface of GaN directly grown on the SAM substrate was observed via high-resolution transmission electron microscopy, and uniform GaN growth on a two-inch SAM substrate was also demonstrated.

Abstract

A small-volume hot-wall batch reactor with excess precursor loading was proposed for supercritical fluid deposition (SCFD) of Cu during the fabrication of sub-millimeter-scale, metal-coated terahertz (THz) wave devices. Conformal film formation was experimentally demonstrated, validating our method. Our method enables a much higher precursor concentration (at least 20 mol/m³) than the conventional method (below 2 mol/m³), facilitating conformal film formation on sub-millimeter structures. Kinetic analysis revealed that our proposed method was applicable for fabricating rectangular metal-coated THz waveguides; furthermore, it was promising for monolithically integrated THz wave devices.

We aimed to identify metallic materials that could be used to construct metal-coated dielectric terahertz (THz) waveguides. We examined seven different metals: gold (Au), copper (Cu), silver (Ag), aluminum (Al), nickel (Ni), chromium (Cr), and titanium (Ti). The propagation losses of our in-house metal-coated dielectric parallel-plate waveguide (PPWG) were experimentally determined. We developed a physical model to estimate the two key parameters determining the performance of metal-coated waveguides: the critical film thickness required for bulk material-like behavior and the propagation loss in a film with a thickness greater than critical film thickness. Film quality, as revealed by the thickness-dependent electrical conductivity of the metal film, was measured prior to experiments and used for model calculations because propagation loss is influenced by film conductivity, which differs from bulk conductivity and depends on film thickness. After experimentally validating the applicability of the model to different metals, suitable metals were identified based on the two key parameters calculated by the model, assuming the same high film quality. Cu was identified as the optimal metal. The effect of film quality on the two key parameters is discussed in this paper. The impact of the surface oxide (CuO_x) layer on THz wave propagation was experimentally evaluated using CuO_x/Cu-coated PPWG; no detectable transmittance decrease was observed regardless of the CuO_x thickness (1.5–176 nm), when the underlying Cu film was of sufficient thickness. Our model also indicated that a CuO_x layer <1  μm-thick had a negligible impact on THz wave propagation. Thus, native oxidation is not an issue when using Cu.

We succeeded in synthesizing a bulk crystal of wurtzite-type boron nitride (w-BN) by the direct conversion method. The synthesized crystal was approximately 2 mm wide and 350 µm thick, and highly oriented to the c-axis. We performed nanoindentation measurements on the c-plane of the w-BN crystal at room temperature to evaluate the mechanical properties of w-BN. The hardness and Young’s modulus of w-BN from the obtained curves were simultaneously determined to be 54 ± 2 and 860 ± 40 GPa, respectively. The underlying physical mechanism that dominates the mechanical properties of group-III nitride semiconductors is also examined.

We investigate copper (Cu) precipitation at small-angle tilt boundaries on (220) in Czochralski-grown p-type silicon (Si) ingots using transmission electron microscopy, atom probe tomography, and ab initio calculations. In the initial stage of precipitation, Cu atoms agglomerate along the boundaries, forming coherent layers (less than about 2 nm thick) of Cu3Si with a body-centered-cubic structure in a metastable state (a = 0.285 nm). As the layers thicken, they become semicoherent with misfit dislocations on the (220) interphase boundaries, reducing coherency strains. Subsequently, the metastable layers convert into incoherent polyhedrons of orthorhombic. eta ''-Cu3Si in the equilibrium state, forming interphase boundaries on {112} in Si. These results are similar to the Cu precipitation processes found in metallic alloys: the formation of Guinier-Preston zones followed by a conversion into the equilibrium theta phase.

Three-dimensional distribution of oxygen atoms at small-angle tilt boundaries (SATBs) in Czochralski-grown p-type silicon ingots was investigated by atom probe tomography combined with transmission electron microscopy. Oxygen gettering along edge dislocations composing SATBs, post crystal growth, was observed. The gettering ability of SATBs would depend both on the dislocation strain and on the dislocation density. Oxygen atoms would agglomerate in the atomic sites under the tensile hydrostatic stress larger than about 2.0GPa induced by the dislocations. It was suggested that the density of the atomic sites, depending on the tilt angle of SATBs, determined the gettering ability of SATBs. (C) 2015 AIP Publishing LLC.

A comparison of ultra-thin insertion layers (Gap and GaP/In0.4Ga0.6P) on InP self-assembled quantum dots (SAQDs) grown on GaAs (001) substrates using metal-organic vapor phase epitaxy (MOVPE) was studied. Atomic force microscopy (AFM) and photoluminescence (PL) were employed to characterize the optical and structural properties of the grown InP QDs. It is found that the QD dimension, size distribution and density strongly depend on the insertion layer thickness which led to tune the emission wavelength and narrowing of full width at half maximum (FWHM) at low temperature (20-250 K) and at room-temperature PL measurements. This result is attributed to the improved QD size and quantum confinement effect arising from the insertion of the GaP and GaP/In0.4Ga0.6P layers. (C) 2013 Elsevier B.V. All rights reserved.

Efficient production of H2 from water without the use of an extra bias or any sacrificial reagents is possible using a GaN photocatalyst with a NiO cocatalyst. The average energy conversion efficiency from light energy to H2 energy was approximately 1% for 500 h. The total amount of hydrogen was 184 mL/cm2 of the GaN surface. H2 production rate was as high as 0.37 mL/(cm2-h). © 2013 The Japan Society of Applied Physics.

We have constructed a system that uses solar energy to react CO2 with water to generate formic acid (HCOOH) at an energy conversion efficiency of 0.15%. It consists of an AlGaN/GaN anode photoelectrode and indium (In) cathode that are electrically connected outside of the reactor cell. High energy conversion efficiency is realized due to a high quantum efficiency of 28% at 300 nm, attributable to efficient electron-hole separation in the semiconductor's heterostructure. The efficiency is close to that of natural photosynthesis in plants, and what is more, the reaction product (HCOOH) can be used as a renewable energy source. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4769356]

Continuous hydrogen generation from water was realized for 110 h using an n-type GaN film with a NiO cocatalyst. This GaN-NiO photocatalyst exhibits incident photon-to-current conversion efficiencies of 70 and 57% at wavelengths of 300 and 350 nm, respectively. These results indicate that the GaN-NiO photocatalyst has high stability and efficiency for hydrogen generation. (C) 2012 The Japan Society of Applied Physics

The effect of thin GaP insertion layers on the structural and optical properties of InP/In0.49Ga0.51P self-assembled quantum dots (SAQDs) on GaAs (001) substrate grown by metalorganic vapour phase epitaxy has been reported. The properties of InP/In0.49Ga0.51P SAQDs are modified when a thin (14 ML) GaP layer is inserted underneath the InP quantum dots (QDs). Deposition of the GaP insertion layer affects the dot dimension and improves the size uniformity. The density, dimension and uniformity of InP QDs strongly depend on the GaP insertion layer thickness. This variation in QD size is a result of a material nucleation effect caused by atomic intermixing between the InP QDs and underlying GaP insertion layer and surface energy. The insertion of GaP layer led to tuning the emission wavelength and narrowing of full width at half maximum (FWHM) when they are characterised by PL measurements at room temperature. (C) 2012 Canadian Society for Chemical Engineering

We have realized for the first time deep-red emission from InGaN-based light-emitting diodes on c-plane sapphire substrates grown by metalorganic vapor-phase epitaxy. The peak wavelength was 740 nm by continuous current injection, in spite of a wide full-width at half-maximum. Indium incorporation was enhanced by a smaller distance of the opposing wall of the reactor from the susceptor, which resulted in raising the gas temperature. In addition, a higher number of quantum wells led to the relaxation of InGaN well layers and thus enhanced indium incorporation. (C) 2012 Elsevier B.V. All rights reserved.

Electrical and physical characteristics of the Al(2)O(3)/InGaAs interfaces with (1 1 1)A and (1 0 0) orientations were investigated in an attempt to understand the origin of electron mobility enhancement in the (1 1 1)A-channel metal-insulator-semiconductor field-effect-transistor. The (1 1 1)A interface has less As atoms of high oxidation states as probed by X-ray photoelectron spectroscopy. The electrical measurements showed that energy distribution of the interface traps for the (1 1 1)A interface is shifted toward the conduction band as compared to that for the (1 0 0) interface. Laterally-compressed cross-section transmission electron microscopy images showed that the characteristic lengths of the interface roughness are different between the (1 1 1)A and (1 0 0) interfaces. The contributions of the Coulomb and roughness scattering mechanisms are discussed based on the experimental results. (C) 2010 Elsevier B.V. All rights reservei.

A strain-balanced InGaAs/GaAsP multiple quantum-wells (MQWs) structure was grown by metal organic vapor phase epitaxy (MOVPE) on GaAs substrate, aiming at a middle cell that improves current matching in a tandem solar cell. In order to detect the instant of strain relaxation in the course of MOVPE, which deteriorates crystal quality significantly, we employed in situ optical surface reflectivity measurement. When strain balancing was incomplete, surface reflectivity dropped during the growth of MQWs, indicating lattice relaxation. Such drop in surface reflectivity occurred at a smaller number of stacked quantum wells when the absolute value of an average strain per well/barrier pair was larger. The accumulated strain, i.e., the product between the average strain and the total thickness at the moment of reflectivity dropped, was roughly constant for all the MQWs, indicating a possibility that we can use this value as the measure to predict the maximum number of MQWs for a given value of the average strain. The reflectance anisotropy (RA) was also monitored in the course of the growth. The value of RA showed linear periodic behavior before the lattice relaxation, corresponding to the well/barrier stacks, suggesting that anisotropy of surface atoms reflects accumulated strain of the growth surface. (C) 2009 Elsevier B.V. All rights reserved.

We have investigated the initial growth of InAs on Si(1 1 1) substrates produced with metal-organic vapor phase epitaxy (MOVPE) and using micro-channel selective area growth (MC-SAG). Treatment of the Si surface prior to InAs growth is essential in order to achieve high-yield nucleation of a single island in each growth area. A breakthrough for successful nucleation was the use of tertiarybutylphosphine (TBP) pre-flow. We have analyzed the effect of such surface pretreatment in terms of the shape of InAs islands at the initial stage of growth and the incubation period between the supply of the indium source and the nucleation, the latter data being obtained by means of in situ surface reflectivity measurement. XPS analyses confirmed that the TBP and tertiarybutylarsine (TBAs) pre-flow introduced, respectively, P and As on the Si surfaces resulting in a change in surface energy. The surface with As exhibited a larger surface energy and shorter incubation period, which are preferable for better nucleation. The coverage of As on the surface, however, appeared less reliable than that of P, i.e., pre-flow with TBP was superior to pre-flow with TBAs in terms of uniformity of surface coverage. This finding is useful for achieving high-yield nucleation in small growth openings in MC-SAG. (C) 2009 Elsevier B.V. All rights reserved.

In order to improve the uniformity of InGaAs lateral islands on Si grown by micro-channel selective area growth, we have investigated the dependences of initial InAs nucleation on the partial pressures of trimethylindium (P(TMIn)) and tertiary butylarsine (P(TBAs)) using the in situ monitoring of surface reflectivity. The high P(TMIn) resulted in a short incubation period, a high density of nuclei, and vertical growth, suggesting that a high P(TMIn) is suitable for obtaining single nuclei in each growth area, which is vital for the growth of single-domain crystals on Si. Laterally grown InAs nuclei, which are preferable for the lateral growth of InGaAs crystals that succeeds the initial nucleation of InAs, were obtained using either a low P(TMIn) or a high P(TBAs), however, the effect of the latter was not significant. P(TBAs) did not affect the incubation period. The density, uniformity, and shape of InAs nuclei can be controlled effectively by adjusting P(TMIn), but the uniformity and lateral shape could not be obtained simultaneously. We, therefore, devised a flow-modulated sequence and obtained InAs islands that grew in the lateral direction and almost filled the growth area with a single-crystal domain. (C) 2010 The Japan Society of Applied Physics

Metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated on the (111)A surface of In(0.53)Ga(0.47)As for the first time. Al(2)O(3) gate dielectrics were formed by atomic layer deposition on sulfur-stabilized InGaAs surfaces. The MISFET on (111)A demonstrated channel mobility higher than that on (100), achieving more than 100% improvement with respect to Si even at a high surface carrier concentration. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/APEX.2.121101

In situ passivation of GaAs surface subsequent to the growth in a metalorganic vapor phase epitaxy (MOVPE) reactor has been made possible using trimethylaluminum (TMAl). The adsorption layer on GaAs, presumably consisting of aluminum and the decomposition product of TMAl, was oxidized upon exposure to air to form thin AlO(x) layer. TMAl supply of only 0.5 monolayer completely prevented the oxidation of As on the surface, as confirmed by XPS. The passivation layer mostly prevented the oxidation of As upon O(2) annealing for 5 min at 250 degrees C. For the successful passivation, complete desorption of excess As on the GaAs surface was essential prior to the injection of TMAl Otherwise, AlAs layer was formed and arsenic oxide was inevitably formed. The optimum length of H(2) purge to desorb As was determined to be 2 min with in situ surface monitoring using reflectance anisotropy spectroscopy (RAS). This passivation method, combined with the succeeding deposition of Al(2)O(3) as a gate dielectric in a different reactor, provides the GaAs/gate interface without As-oxide. The method is applicable to the MOVPE growth of electron channel layers containing As for III-V metal-insulator-semiconductor field effect transistors (MISFETs). (C) 2008 Elsevier B.V. All rights reserved.

In this paper, we demonstrate that micro selective area growth (mu SAG) is effective in improving the crystal quality of InGaAs oil (111) Si through the decrease in the number of the nuclei on a selective growth Si area. It is found that smaller selective areas are better in the morphology of the epitaxial films, while the pitch of selective areas yields a trade-off relationship between the selectivity and the lateral growth length. It is demonstrated that InGaAs films with good morphology and largo lateral growth areas have been obtained by mu SAG on (111) Si dot areas with the diameter of 2 mu m and the pitch of 5 mu m using metal-organic vapor phase epitaxy (MOVPE). This result suggests that mu SAG using MOVPE is a promising technique for III-V-On-Insulator structures oil Si substrates. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ reflectance anisotropy spectroscopy was employed to interpret the surface reaction rate constant (k(s)) of a Ga precursor on a GaAs(001) surface in metallorganic vapor-phase epitaxy (MOVPE), which was extracted by the analysis of selective-area growth. The activation energy of ks significantly decreased above 625-630 degrees C. Correspondingly, the surface anisotropy spectrum changed around 600 degrees C from that of surface reconstruction containing Ga dimers at lower temperatures to that of c(4 x 4)-like reconstruction with As dimers at higher temperatures. These observations suggest a step-flow growth mode at higher temperatures and an island growth mode at lower temperatures. (c) 2007 The Electrochemical Society.