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• MOCVD reactor and models the gas flow, chemical kinetics & surface diffusion. • Atomistic scale innovative MOCVD growth: AIXTRON 200/4 RF-S reactor geometry. • Gas & surface chemical kinetics and thermodynamics, without using continuum models. • Optimum conditions achieved by designing experiments on TNL-EpiGrow simulator. • Excellent agreement is observed between experimental and simulated results. In present paper an innovative technique to reproduce the epitaxial growth results through lateral flow metal organic chemical vapor deposition (MOCVD) reactor process at atomistic scale is reported. It includes the equivalent MOCVD reactor geometry architecture of AIXTRON 200/4 RF-S horizontal flow reactor. The gas- and surface phase chemical reaction kinetics and thermodynamics are given due consideration in the present study without use of any continuum or fluid dynamics models. The optimum conditions are extracted by running design of experiments over TNL-EpiGrow simulator to achieve high crystalline quality aluminum nitride (AlN) films over Si (1 1 1) substrate. The impact of variation in precursor NH 3 flow rates and carrier gas N 2 pressure are used to predict the conditions to optimize the improved morphology and quality of the AlN films. The defects densities are characterized in terms of vacancies and dislocation densities. The roughness and lattice parameters are extracted. The growth rates obtained in present studies are compared against reported the similar experiments. The excellent agreement is observed between experimental and simulated results. The dislocation densities in grown samples are also found in good agreement with the similar experimental reported densities in each sample. [ABSTRACT FROM AUTHOR]

High crystalline quality of AlN layers are commonly grown at temperatures above 1200 °C. However, this work revealed that introducing a rough surface of AlN layer, defined as dislocation filtering (DF) herein, can improve the crystalline quality of 1.5 μm thick AlN layers grown at 1175 °C via metal organic vapor phase epitaxy technique. With 7 slm of ammonia flow during the DF growth, the lowest threading dislocation density (TDD) of ∼2.9 × 109 cm−2 was obtained. The result was associated to the formation of 3D growths which become reasonably smaller, denser, and more uniformly distributed with increasing ammonia flow up to 7 slm. The 3D growths were suggested to promote lateral growth that can increase the possibility for TD inclination and hence, mutual annihilation. The 3D growths characteristic disappeared when the ammonia flow was 10 slm. The optimized AlN layer that was obtained with 7 slm of ammonia flow exhibited an atomically smooth surface with a few deep trenches and improved transparency. Meanwhile, the calculated in-plane tensile strain for the AlN layers grown on DF with 1–7 slm of ammonia was about 3 times higher than the AlN layer without DF. However, no evidence of microcracks on the surface was observed. • With 7 slm ammonia flow during DF (dislocation filtering) growth, the lowest TDD of AlN was ∼2.9 × 109 cm−2. • AlN surface and transparency improved with DF, especially with 5 and 7 of ammonia flow. • In general, DF increased tensile strain but no microcracks was observed. [ABSTRACT FROM AUTHOR]

In this work, a dual-sided buffer template, which allows the deposition of YB 2 Cu 3 O 7-δ (YBCO) coated conductors on both sides, has been proposed and investigated. Theoretically, in contrast to traditional YBCO structure on one side, the performance of critical current in YBCO films has been improved by two times. In this buffer structure, the dual-sided Y 2 O 3 films were grown on a flexible metal template by a home-made reel-to-reel dynamic direct current sputtering system and the film growth parameters were systematically investigated. The microstructure were characterized by in situ reflection high-energy electron diffraction monitoring in real time during the deposition stage. X-ray diffraction, and atomic force microscopy were used to detect the biaxial texture and surface morphology, respectively. What's more, by the application of stopping and range of ions in matter software, it helped us to understand the influence of deposition parameter to the growth rate of Y 2 O 3 films. Finally, the biaxial texture of dual-sided Y 2 O 3 film yielded out-of-plane texture of Δ ω = 4.2° and in-plane texture of Δ Φ = 5.2° for one side, as well as Δ ω = 5° and Δ Φ = 5.3° for the second side. Subsequently, the dual-sided YBCO superconducting films were coated on the above Y 2 O 3 buffer layer by low-cost metal-organic chemical vapor deposition method with critical current of 30 A/cm and 60 A/cm for each side. [ABSTRACT FROM AUTHOR]

This study investigates that high-quality GaN thin films can be grown on a few-layer graphene (FLG)/sapphire substrate by embedding a hybrid AlN buffer layer (BL). The hybrid AlN BL is constructed by low-temperature AlN nucleation layer (LT-AlN NL) and high-temperature AlN BL grown respectively by sputtering and metal organic chemical vapor deposition (MOCVD). The high density of edge-type threading dislocation (TD) in the GaN sample without hybrid AlN BL provide current leakage paths, resulting in a symmetric and temperature-independent I-V characteristic curve for a Ni-based Schottky contact. The excellent adhesion and uniform coverage of LT-AlN NL on the FLG layer by sputtering can overcome the nucleation issue and prevent the thermal etching effect of graphene during MOCVD epitaxial process. The edge-type TD density and carbon concentration of the GaN thin films grown on the hybrid AlN BL/FLG/sapphire substrate can be reduced significantly, resulting in a lower intensity of blue, green, and orange luminescences on a 17-K photoluminescence spectrum. The Ni-based Schottky contact with a barrier height of 0.69 eV and leakage current density of 4.38 × 10−6 A/cm2 is obtained, which demonstrates that a high-quality GaN thin films can be grown onto an FLG substrate by embedding a hybrid AlN BL. Unlabelled Image • Graphene dissociation is suppressed by embedding a hybrid AlN buffer layer. • High crystalline quality of GaN thin-films is grown on a graphene substrate. • A PTC characteristic of Ni/GaN Schottky diode is obtained on a graphene substrate. [ABSTRACT FROM AUTHOR]

Highlights • A high-resolution time-of-flight mass spectrometry system was employed. • In-situ monitoring of vapor phase reaction was demonstrated. • Decomposition of NH 3 in the simple reactor was measured. Abstract The decomposition of ammonia (NH 3) in nitrogen (N 2) ambient was studied under non-equilibrium conditions similar to those in a metal organic vapor phase epitaxy (MOVPE) reactor during the epitaxial growth of group-III nitrides. The gas phase was sampled at different positions and analyzed using a time-of-flight mass spectrometry system with a high resolution (better than 0.002 u). Our results expand earlier findings. Even at the high temperature of 1200 °C, only 26% of NH 3 decomposed in a clean metal-free reactor, whereas a higher ratio of NH 3 decomposition was realized in the presence of stainless steel. The activation energy in the clean reactor was calculated to be 0.965 ± 0.004 eV. These results demonstrate the capability of our setup and shed new light on the elucidation of the vapor phase growth mechanism of group III-nitrides by MOVPE. [ABSTRACT FROM AUTHOR]

Abstract Epitaxial GaAs nanostructures have been grown on GaAs (111)B surface by metal organic chemical vapor deposition (MOCVD) using in situ self assembled Gallium (Ga) droplets as catalyst. The effect of growth pressure and time on the shape, size, and surface density of nanostructures grown under Arsenic (As) deficient conditions has been studied in detail. Good optical quality nanostructures in high yield and uniformity could be grown at 420 °C using catalyst droplets having a size of 350 nm. The optical quality of the nanostructures was confirmed with photoluminescence (PL) and Raman measurements. An unconventional decrease in the size of the nanostructures and formation of undesired streaky features were noticed on prolonging the growth from 10 to 20 min under Arsenic deficient conditions used in this study. Lowering the growth pressure from near atmospheric to 100 Torr has also led to a drastic decrease in the size and density of the nanostructures. At 450 °C, interestingly, almost flat hexagonal GaAs nanostructures with thickness ∼25 nm have been obtained in surplus yield in samples grown under 100 Torr. A growth model on the basis of progressive consumption of catalyst droplet during the growth has been proposed to explain these findings. The droplet consumption rate ∼25 nm/min has been estimated at 420 °C and 660 Torr from detailed analysis of the growth results. Highlights • Growth of high optical and crystalline quality GaAs nanostructures in high yield and uniformity by self catalysis. • Consumption of Gallium catalyst during the growth leading to tapering. • Nanostructure 'melt away' under Arsenic deficient conditions and formation of streaky features. • Growth of almost flat hexagonal GaAs nanostructures in surplus yield at low pressure. [ABSTRACT FROM AUTHOR]

Highlights • Growth of InGaAs nucleation with single domain on Si(1 1 1). • Growth of InGaAs self-aligned pillar on Si(1 1 1). • Significant improvement in InGaAs islands' crystal quality and uniformity. • Unique atomic step patterns on InGaAs (1 1 1) facet by AFM, demonstrating atomic layer by layer growth. • Free of threading dislocation. Abstract We report successful growth of threading dislocation free InGaAs island arrays on masked Si(1 1 1) substrate by micro-channel selective area growth (MC-SAG). Developed from InGaAs/InAs/Si growth scheme (Deura et al., 2009) [1], InGaAs nucleation and pillar layer are originally introduced before the lateral growth in order to reduce the InGaAs/InAs lattice mismatch, leading to significant improvement in both crystal quality and uniformity. Unique atomic step patterns along 〈1 1 0〉 directions are observed on InGaAs (1 1 1) facet by AFM, demonstrating atomic layer by layer growth. No threading dislocation is detected. This scheme can be a very promising approach for high level III-V on Si integration. [ABSTRACT FROM AUTHOR]

Highlights • Misorientation on the (1 0 0) substrate can promote island nucleation. • Lower growth rate is favorable in obtaining an even buffer layer surface. • Corrugated buffer surfaces found to introduce order in the arrangement of the dots. • The troughs on corrugated surface enhances nucleation of 3D islands. • The shape and size of the dots are responsive to the thickness of the buffer layer. Abstract The dependence of optimum V/III ratio on substrate orientation and the influence of buffer layer on the growth of InSb/GaSb quantum dots (QDs) using atmospheric pressure Metalorganic Vapor Phase Epitaxy (MOVPE) are investigated in this study. The misorientation on the (1 0 0) substrate is suggested to enhance the formation of surface steps, which provides low energy growth sites and hence promotes island nucleation. An increase in V/III ratio from 1.0 to 3.0 resulted in a significant reduction in dot density on both (1 0 0) and (1 1 1) substrates, a phenomenon attributed to the reduced number of indium adatoms available on the growth surface, which simultaneously stimulates a decrease in the migration length of indium species. The shape and size of the dots were observed to be sensitive to the thickness of the buffer layer. Likewise, an increase in buffer layer thickness from 50 nm to ∼300 nm shows the onset of surface corrugation for buffer layer thickness of ∼150 nm, which persisted up to a buffer thickness of ∼250 nm. The corrugated buffer surfaces were observed to introduce order in the arrangement of the dots, which formed preferentially inside the troughs. A reduction in growth rate (from 0.21 to 0.17 nm/s) is presumed to induce sufficient adatom migration and strong bonding between the adsorbate atoms which results in an even buffer layer surface due to an enhancement in surface coverage of adatoms. [ABSTRACT FROM AUTHOR]

Highlights • 50 years of MOVPE. • Manasevit's early research reviewed. • Early MOVPE research reactors. • Development of vertical rotating-disk MOVPE reactor. • Major MOVPE reactor platforms for production. Abstract MOVPE technology has rapidly grown from a laboratory research novelty in the 1960's to the dominant production method for epitaxial materials used in high-performance compound semiconductors devices. In order for MOVPE to be adopted as an efficient and high-yield process, the MOVPE reactor had to be designed and operated in a manner to produce uniform epitaxial layer structures with a high degree of controllability and reproducibility. In commemoration of 50 years of MOVPE technological advancement, this paper reviews the early history of MOVPE reactor development and foundational advances that were critical for development of multi-wafer capacity production reactors having high yield and reproducibility. [ABSTRACT FROM AUTHOR]

Abstract A method for the growth of high quality GaSb epilayer on GaAs (001) substrate is demonstrated in this study. It is found that a superior GaSb/GaAs interface can be obtained by depositing a thin Sb-precursor layer on the GaAs substrate containing a GaAs buffer layer. It is suggested that the growth occurs via the interface misfit (IMF) growth mode. Without this treatment, GaSb epilayer may grow according to the Stranski–Krastanov mechanism or via a blend of the Stranski–Krastanov and IMF mechanisms, leading to an inferior GaSb/GaAs interface. This could be due to the intermixing of anions, leading to the turbulent composition and misfit dislocation distribution at the heterointerface. It appears that with the addition of a Sb layer, IMF arrays can be formed at GaSb/GaAs interface resulting in superior GaSb layer without the need for changing the growth parameters. Highlights • Impact of Ga- and Sb-based passivation at the GaSb/GaAs interface was studied. • Sb-based passivation relaxes the GaSb/GaAs lattice strain. • Sb-based passivation reduces threading dislocations at the GaSb epilayer. • Sb-based passivation prevents the interdiffusion at the GaSb/GaAs interface. [ABSTRACT FROM AUTHOR]

Highlights • Nanocones were prepared by Metal Organic Vapour Phase Epitaxy. • Nanocones were fully covered by Ag nanoparticles deposited from aqueous solution of silver nitrate. • A part of nanocones under study was covered by thin layer of Molybdenum disulphide. Abstract Zinc-doped gallium phosphide (GaP) nanowires and nanocones were grown by metal organic vapour phase epitaxy (MOVPE) on GaP〈1 1 1〉B substrates by a VLS technique using 30 nm colloidal gold particles as seeds. The growth was performed in an AIX 200 MOVPE low-pressure reactor between 500 and 690 °C. As the growth temperature T g was increased, GaP nanocrystals changed their shape from rod-like nanowires at 500 °C through tapered nanocones at between 610 and 660 °C and finally to biconical shape at 690 °C. The nanocones had hexagonal cross-sections at their bases following the orientation of the substrate. GaP substrates were nanostructured with nanowires or nanocones with the aim to create experimental platforms for further exploration namely for (1) the deposition of Ag nanoballs that should facilitate surface enhanced Raman scattering, and (2) the synthesis of a thin molybdenum disulphide (MoS 2) layer that would be suitable for solar cell and water disinfection applications. [ABSTRACT FROM AUTHOR]

Boron nitride films were grown on 2-inch sapphire substrates using the MOCVD technique. The growth was performed using a pulsed source injection mode with triethylborane (TEB) and ammonia (NH 3 ) with a high V/III ratio, which corresponds to the self-terminated growth mode. Two different carrier gases, H 2 and Ar, were used to investigate their influence on the growth mechanism, while all the other growth parameters were kept the same. The BN films thus obtained were examined using XRR, SIMS, Raman spectroscopy, ATR spectroscopy, SEM and AFM. A difference was found in the surface roughness. The BN films grown in an H 2 atmosphere had a surface roughness three times smoother than those grown in Ar. However, the main difference was brought to light by SIMS measurements. The SIMS measurements revealed that growth under an H 2 flow leads to a reduction in carbon concentration by more than four orders of magnitude. It was also shown that the boron distribution in the BN film grown under an H 2 flow is very uniform. It is discussed that this mechanism is related to the reactions between TEB and NH 3 in the presence of H 2 . The elimination of carbon by using hydrogen reveals its role in BN growth, which is indeed essential. [ABSTRACT FROM AUTHOR]

Realization of high efficiency III-V-on-Si solar cells requires preparation of an oxygen free Si substrate surface, which allows for subsequent antiphase domain free III-V epitaxy. For GaAsP/Si tandem cells, the impact of As on established Si processing in metal organic vapor phase epitaxy (MOVPE) is essential. Here, we study the interaction of As with vicinal Si(100) surfaces, the formation of atomically well-ordered As-modified Si(100) surfaces, and its impact on subsequently grown GaP epilayers. We apply optical in situ spectroscopy during MOVPE and show that process routes strongly affect the formation of double-layer steps on Si(100). We demonstrate that exposure to As, together with HF pre-treatment, enables processing of suitable Si(100) 2° and 6° offcut surfaces at temperatures below 820 °C. Subsequently grown GaP epilayers exhibit smooth surfaces free of antiphase disorder and distinct Laue oscillations in X-ray diffraction. Such low temperature processing, which is controllable in situ , is promising for further metamorphic GaAsP integration. [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of conductive Si-doped β-Ga 2 O 3 films on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD) was successfully performed. The effect of Si content on the structural, morphological, electrical and optical properties of Si-doped β-Ga 2 O 3 films was investigated in detail. Distinctive surface morphology evolution of films depending on Si content was observed and presented. The Si-doped β-Ga 2 O 3 films exhibited high transmittance in the ultraviolet-visible regions. The temperature-dependent PL was carried out especially to discuss the photoluminescence properties of Si-doped β-Ga 2 O 3 films. More importantly, the results suggested that the conductivity of heteroepitaxial Si-doped β-Ga 2 O 3 films by MOCVD could be realized and controlled by adjusting the Si content. The minimum resistivity of 1.79×10 −1 Ω·cm was obtained for the films grown under the SiH 4 flow rate of 0.08 sccm. [ABSTRACT FROM AUTHOR]

Commercially, semiconductor thin films for use in electronic devices are typically produced by processes such as chemical vapor deposition. This requires the gas flow, heat distribution, and concentration distribution above the substrate in the reactor to be carefully controlled to ensure that the growth rate and thickness uniformity of the thin film are appropriate. This work involved the simulation of a gallium nitride metal-organic chemical vapor deposition (GaN-MOCVD) reactor with a vertical spray structure. The simulation, which was conducted by using computational fluid dynamics software, enabled us to obtain a numerical solution under steady-flow low-pressure conditions with substrate axisymmetrical rotating. The temperature field, flow field, operating pressure, and rotation speed of the substrate were analyzed, and process conditions were optimized. These conditions make it possible to stabilize the flow field in the reactor to ensure thickness uniformity of the deposited thin film. These results not only provide an effective solution for high-quality epitaxial growth, but also provide a theoretical basis for follow-up experiment and equipment improvement. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH 3 ) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH 3 is supplied to fully convert the TEB within one cycle. Excess NH 3 caused islands on h-BN film surface while a lack of NH 3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c -plane sapphire was confirmed to be [0001] h-BN ∥[0001] sapphire and [10-10] h-BN ∥[11-20] sapphire . It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. [ABSTRACT FROM AUTHOR]

Epitaxial SnO 2 films were deposited on MgF 2 (110) substrates at different substrate temperatures by the metal organic chemical vapor deposition (MOCVD) method. The structural, optical and electrical properties as well as elementary composition were studied in detail. The obtained films were all rutile phase SnO 2 grown along the [110] direction. The SnO 2 film prepared at 660 °C was single crystalline epitaxial film. The epitaxial relationships were clearly determined as SnO 2 (110) || MgF 2 (110) with SnO 2 [001] || MgF 2 [001]. The Hall mobility of the 660 °C-deposited film was 21 cm 2 V −1 s −1 with a carrier concentration of 3.9 × 10 17 cm −3 . The average transmittance of the 660 °C-deposited film in the visible range is 93% and the optical band gap is estimated as 3.89 eV. [ABSTRACT FROM AUTHOR]

Epitaxial lateral overgrowth (ELO) process of gallium nitride (GaN) films on cone-shaped patterned sapphire substrate (PSS), which was pretreated by ion-implantation was performed by using a metal organic chemical vapor deposition. A 250-nm-thick silicon dioxide (SiO 2 ) mask was covered on the planar surface of the PSS to protect them from ion-implantation damages, whereas the cone-shaped patterns of the PSS were exposed to collide with the N + ions. The ion-implantation pretreatment was selectively carried out on the cone-shaped pattern of PSS at 67.5 keV with a high dose of 5 × 10 17 cm − 2 . As a result of ion-implantation pretreatment, nucleation growth of GaN poly-grains was inhibited on the cone-shaped patterns with various crystal planes, such as c-like plane, R-like plane, and n-like plane. Surface roughness and crystal quality of GaN films grown on ion-implanted PSS were improved owing to the inhibition of nucleation growth on the patterns. The ion-implantation pretreatment is a very promising technique in the ELO process of GaN on an uneven substrate such as a cone-shaped PSS that includes various crystal planes. [ABSTRACT FROM AUTHOR]

We report on the growth of epitaxial β–Ga 2 O 3 thin films on c-plane sapphire substrates using a close coupled showerhead MOCVD reactor. Ga(DPM) 3 (DPM = dipivaloylmethanate), triethylgallium (TEGa) and trimethylgallium (TMGa) metal organic (MO) precursors were used as Ga sources and molecular oxygen was used for oxidation. Films grown from each of the Ga sources had high growth rates, with up to 10 μm/hr achieved using a TMGa precursor at a substrate temperature of 900 °C. As confirmed by X-ray diffraction, the films grown from each of the Ga sources were the monoclinic ( 2 ¯ 0 1) oriented β–Ga 2 O 3 phase. The optical bandgap of the films was also estimated to be ∼4.9 eV. The fast growth rate of β–Ga 2 O 3 thin films obtained using various Ga-precursors has been achieved due to the close couple showerhead design of the MOCVD reactor as well as the separate injection of oxygen and MO precursors, preventing the premature oxidation of the MO sources. These results suggest a pathway to overcoming the long-standing challenge of realizing fast growth rates for Ga 2 O 3 using the MOCVD method. [ABSTRACT FROM AUTHOR]

Integration of GaP layers on silicon substrates using AsH 3 pre-exposure followed by a PH 3 -based GaP epitaxial growth allows the development of very promising processes for the photovoltaic industry, although many of the growth routines using this approach suffer from reproducibility issues when transferred to a new epitaxial system, leading to poor quality layers. This fact reveals a lack of knowledge on the mechanisms behind the formation of the most common planar defects (stacking faults and microtwins) and their dynamics for GaP/Si Metal Organic Vapor Phase Epitaxy using AsH 3 and PH 3. Therefore, in this work, a set of GaP/Si samples with a similarly high defect density grown between 700 °C and 725 °C, are analyzed by means of high-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. The results presented show contaminant-free Si surfaces for temperatures above 725 °C, ruling out the hypothesis of contaminant as the origin of these planar defects. Regarding the interface Si/GaP, the GaP growth starts, in all the samples, with Ga Si bonds. Additionally, no traces of As are found, which reinforces the hypothesis of an effectively displacement of As on Si surface by Ga atoms at high temperature. Finally, it is observed complex chemical structures in the origin of the microtwins and the cause of the origin of these defects seems to be a localized gallium depletion at the GaP/Si interface. [Display omitted] • We have studied the mechanisms involved in the formation of flat defects due to GaP/Si epitaxial MOVPE growth at high temperature and AsH3 pre-exposure. • The effect of different AsH3 pre-exposure parameters (i.e. temperature, and time) on the morphological and structural quality of the GaP layer has been assessed. Samples have been characterized by means of HRTEM, STEM, and EELS. • The combination of the different techniques reveals that in all cases the planar defects originate in the GaP/Si interface. • It has been demonstrated that the formation of planar defects is not related to the presence of O in the GaP/Si interface. • It has been observed that the formation of planar defects is linked to the interruption of the Ga-dimers on the Si surface [ABSTRACT FROM AUTHOR]

Single-junction Ge solar cells have been epitaxially grown on GaAs (001) substrates by a low pressure metalorganic chemical vapor deposition using isobutylgermane. Various growth conditions have been studied to reduce the high doping level of over 1×10 19 cm −3 of the p-type Ge epitaxial layer, which is detrimental to the minority carrier collection efficiency. By increasing the growth rate and employing a discontinuous doping technique, the p-type doping level of the epitaxial Ge layer has been lowered to 2×10 18 cm −3 , and the hole mobility increased from 44 to 162 cm 2 /V s. A high power conversion efficiency of 6.72% can be achieved under AM1.5 G illumination by the epitaxial Ge solar cell with the lowered doping level in the p-type Ge base region. The spectral response of the epitaxial Ge solar cell with a 5 µm thick base layer is good enough to use for InGaP/GaAs/Ge triple-junction solar cells. [ABSTRACT FROM AUTHOR]

Hillocks on N-face GaN (000 1 ¯ ) films are effectively eliminated by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH 3 . A hillock-free smooth surface obtained by group-III-source FME is attributed to the enhancement of step-flow growth. We found that a hillock originates from a micropipe and grows by spiral growth around the micropipe. The spiral growth rate rapidly decreases with decreasing the degree of surface supersaturation σ , while the step-flow growth rate decreases linearly. For group-III-source FME, wherein σ is lower than conventional continuous growth, the spiral growth rate could be lower than the step-flow growth one so that the formation of hillocks is suppressed. [ABSTRACT FROM AUTHOR]

We have studied the photoluminescence and electrical properties of ZnO films grown epitaxially by atmospheric pressure MOCVD on 4H-SiC substrates. The dominating D°X line on the low temperature PL spectrum is attributed to the emission of an exciton bound to the neutral donor. The intensity of this line correlates with the electrical properties of the films: the decrease of D°X intensity occurs simultaneously with the increase of the carrier׳s mobility. This we explain as donor activation providing free electrons to the conduction band. Based on the comparison of the calculated value of donor binding energy, the literature data and complementary SIMS analysis a suggested donor impurity is aluminum (Al). The exciton localization energy is 16.3 meV, and agrees well with localization energy of 15.3 meV for Al impurity reported by other authors (e.g. Ref. [33] ). The thermal activation energy E D =22 meV, determined from the Hall data and is in agreement with the optical activation energy ~20 meV, which is derived from the temperature-dependent PL study. The calculated value of the donor binding energy of 54.3 eV is in agreement with the ionization energy of 53 meV mentioned in earlier reports for Al in ZnO films. Our results prove that the commonly observed line at ~3.3599 eV on low temperature PL spectra of ZnO is a neutral donor bound exciton emission due to the Al impurity. [ABSTRACT FROM AUTHOR]

• The subband energy levels of the structure change significantly with the EM field. • The position of the PL peak shifts to lower energies with temperature. • The position of the PL peak shifts to lower energies with potential height. In this study, the photoluminescence measurements of GaAs / A l 0.25 G a 0.75 As multi-quantum-wells heterojunction structure grown on n+ - GaAs substrates by Metal Organic Vapor Phase Epitaxy (MOVPE) method are investigated. By dropping 5145 Å wavelength laser light on the sample at room temperature and low temperatures, the transitions between the bands in the structure and the changes in these transitions under the different electric fields and temperatures are observed. In addition, by making theoretically developed self-consistent potential calculations, the subband energy levels and their corresponding wave functions of the structure under the electric field and without the electric field are calculated. The obtained numerical results were found to be in full agreement with the experimental measurements and theoretical calculations. [ABSTRACT FROM AUTHOR]

In this article, the authors have investigated the optimization of the buffer thickness for obtaining high-quality ZnO epi-films on sapphire substrates. The growth mechanism of the buffers with different thickness has been clearly revealed, including the initial nucleation and vertical growth, the subsequent lateral growth with small grain coalescence, and the final vertical growth along the existing larger grains. Overall, the quality of the buffer improves with increasing thickness except the deformed surface morphology. However, by a full-scale evaluation of the properties for the epi-layers, the quality of the epi-film is briefly determined by the surface morphology of the buffer, rather than the structural, optical, or electrical properties of it. The best quality epi-layer has been grown on the buffer with a smooth surface and well-coalescent grains. Meanwhile, due to the huge lattice mismatch between sapphire and ZnO, dislocations are inevitably formed during the growth of buffers. More importantly, as the film grows thicker, the dislocations may attracting other smaller dislocations and defects to reduce the total line energy and thus result in the formation of V-shape defects, which are connected with the bottom of the threading dislocations in the buffers. The V-defects appear as deep and large hexagonal pits from top view and they may act as electron traps which would affect the free carrier concentration of the epi-layers. [ABSTRACT FROM AUTHOR]

New manufacturing processes were proposed to evaluate important photovoltaic properties of each subcell in an InGaP/InGaAs/Ge triple-junction solar cell. In addition to the triple-junction cell, an InGaAs/Ge double-junction cell and a Ge single-junction cell were also fabricated and employed for evaluation. The key merit of the double-junction cell is that semiconductor layers of forming InGaP top subcell are retained as a dummy top subcell. Thus, the InGaAs middle subcells in both triple- and double-junction cells will receive the same light spectrum. Similarly, the Ge single-junction cell is fabricated with dummy top and middle subcells as light filters. Open-circuit voltage, short-circuit current, conversion efficiency, and current mismatched ratio were measured for evaluating and optimizing each subcell. It is found that Open-circuit voltages are 1.295, 0.967, and 0.212 V for the InGaP, InGaAs, and Ge subcells with temperature coefficients of −2.5, −1.99, and −1.87 mV/°C. Thus the Ge subcell no longer acts a real solar cell at temperature over ∼140 °C. Besides, effect of ambient temperature on short circuit currents of all as-fabricated solar cells is not relevant. The current mismatched ratios are 18.6–20% at temperature ranged from 25 °C to 80 °C. A low efficiency of ∼18.7% is due partly to the poor current match. However, the processing concept proposed is useful as a method of matching currents among the subcells. [ABSTRACT FROM AUTHOR]

We report three dimensional (3D) disk-shaped GaAs crystals on V-groove patterned (001) Si substrates by metalorganic chemical vapor deposition. Planar GaAs nanowires with triangular cross-sections were grown inside Si V-grooves by nano-scale selective heteroepitaxy. These nanowires were then partially confined in micro-sized SiO 2 cavities and coalesced into uniform arrays of 3D crystals. Scanning electron microscope and atomic force microscopy inspection showed the absence of antiphase-domains and smooth top surface morphology. Superior structural and optical properties over GaAs thin films on planar Si were also demonstrated. More remarkably, by growing the 3D crystals on V-grooved Si, we were able to overcome the residual tensile stress induced by the thermal mismatch between GaAs and Si. Strain-free GaAs was uncovered in the crystals with a dimension of 3×3 µm 2 . [ABSTRACT FROM AUTHOR]

High-quality single-crystal anatase TiO 2(a-TiO 2) thin films have been obtained on SrTiO 3 (STO) substrates using the metalorganic chemical vapor deposition (MOCVD) method. The optimal preparation process was explored. The lattice structure and epitaxial relationship were investigated by X-ray diffraction (XRD, both θ −2 θ and Φ scans) and transmission electron microscopy (TEM). The results indicated that the film prepared at 550 °C with the Ti precursor molar flow rate of 4×10 −7 mol/min had the best single crystalline quality, for which a clear epitaxial relationship of a-TiO 2 (001)||STO (100) with a-TiO 2 [100]||STO [001¯] could be inferred. The elemental composition and proportion were studied by the X-ray photoelectron spectroscopy (XPS) method, which proved the deposited film approximated stoichiometric TiO 2 . The samples showed high transparency of 70–80% in the visible range. [ABSTRACT FROM AUTHOR]

The delivery rates of liquid or solid MOCVD precursors depend on the temperature of the liquid precursor inside its container which is also referred to as bubbler, the total pressure inside the container and the carrier gas flow. For use in the CVD process, the liquid precursor is evaporated and transported to the process by use of a carrier gas. The evaporation process requires heat. Unless this heat is provided through a heater, the precursor will cool and the vapor pressure will drop. For high carrier gas flows and large capacity, short bubblers that are commonly used in III–V semiconductor epitaxy production today, we found that the temperature drop and the associated vapor pressure drop will change considerably over the life of the bubbler as the precursor liquid is depleted. For best control of the process (and highest yield), it is beneficial to have a mathematical expression that predicts the expected output concentration over the life of the bubbler. The mathematical expression that we present here uses the carrier gas flow, the precursor level and the aspect ratio of the bubbler as input to predict the expected concentration shift and an associated compensation factor for the carrier gas flow. The mathematical expression uses two fitting parameters. We determined these parameters for TMGa by the measurement of the output concentration from cylinders of different shape under various flow conditions and liquid levels. [ABSTRACT FROM AUTHOR]

The effect of silicon doping on the growth and properties of ∼ 1.0 μ m - thick Al x Ga 1 - x N ( 0.50 ≤ x ≤ 0.55 ) layers grown on semipolar ( 11 2 ¯ 2 ) AlN templates by metalorganic vapour phase epitaxy was studied. The layers were grown with different disilane/group-III precursors ratios that varied from 2.8×10 −5 to 3.4×10 −4 . The surface morphology of the Si-doped ( 11 2 ¯ 2 ) AlGaN layers showed undulations along [ 1 1 ¯ 00 ] AlGaN , AlN with a root-mean square roughness of about 4.0 nm within a scan range of 20 × 20 μ m 2 . Different photoluminescence peaks have been linked to negatively charged cation vacancies ( V III 3 − ) and their complexes with impurities such as V III 3 − - 3 O N 1 + , (V III complex) 1− , and (V III complex) 2− . The optimised AlGaN:Si layer exhibited a carrier concentration of ∼1.2×10 19 cm −3 , a carrier mobility of 30.7 cm 2 /V s, and a resistivity of 0.018 Ω cm , as determined by Hall-effect measurements at room temperature. A correlation between the resistivity and luminescence emission intensities of AlGaN near-band-edge and impurity-related complexes was found. [ABSTRACT FROM AUTHOR]

Metal-semiconductor-metal (MSM) structured solar blind photodetectors were fabricated based on various Mg content wurtzite Mg x Zn 1−x O epitaxial films grown via pulsed metal organic chemical vapor deposition. The response spectra of the devices showed a peak position that shifts from ∼383 nm to 276 nm for Mg content, x , between 0.0 and 0.51, covering a wide portion of the ultra-violet spectral region, extending well into the solar blind window. At 10 V bias, a large responsivity of ∼1.8 × 10 4 A/W was obtained at 276 nm for a device based on a high Mg content (x = 0.51) MgZnO film. To the best of our knowledge, this responsivity is the highest ever reported for a MgZnO based device and its origin is attributed to large internal gain resulting from carrier trapping at the MgZnO/Ni/Au interface. This is confirmed by the presence of an asymmetric Schottky barrier height on the two MSM contacts. Conversely, the response speed of the devices was slow with the 10%–90% rise and fall times measured to be in the millisecond range. The results reported in this work show the realization of high responsivity MgZnO based solar blind photodetectors, providing a significant step in the development of MgZnO alloy based of detector. [ABSTRACT FROM AUTHOR]

The structural characteristics of epitaxial Ge 1 Sb 2 Te 4 deposited by MOVPE are reported. X-ray diffraction, electron backscatter diffraction as well as high resolution transmission electron microscopy were carried out. The Ge 1 Sb 2 Te 4 layers crystallize in the trigonal space group R 3 ¯ m with lattice constants a = 4.27 Å and c = 41.0 Å (in hexagonal description). Seven alternating anion and cation layers forming blocks separated by (van der Waals) gaps oriented parallel to the Si ( 111 ) substrate can be used to describe the structure. Except for the formation of crystallographic twins (rotation by 60 ° around the [ 0001 ] direction), no other defects are found. The results indicate the existence of mixed cation layers and a stacking sequence (Ge 0.5 Sb 0.5 )-Te-(Ge 0.25 Sb 0.75 )-Te-Te-(Ge 0.25 Sb 0.75 )-Te. The structural relation to interfacial phase change memories based on superlattices is discussed. [ABSTRACT FROM AUTHOR]

Complex studies of intentional GaN carbon doping from propane during MOVPE were performed in a wide range of growth conditions. A strong dependence of carbon doping efficiency on growth rate and ammonia flow is revealed, while dependence of carbon doping efficiency on reactor pressure is small. Atomic force microscopy confirms the good quality of the GaN:C layers for doping levels as high as 2*10 19 cm −3 grown with growth rate up to 45 μm/h. The dependence of carbon incorporation into GaN is proportional to the propane concentration to the power 3/2 in most growth regimes, but for very high growth rate a linear or sub-linear component of the dependence becomes prominent. [ABSTRACT FROM AUTHOR]

The present work is part-I of a study that demonstrates the influence of metalorganic chemical vapor deposition process parameters on the evolution of gallium nitride (GaN) deposited in a two-step growth process on c-plane sapphire substrates with a particular emphasis on nitrogen-polar GaN (N-polar GaN). First, the temperature domains of sapphire nitridation that result in Ga-polar and N-polar GaN epilayers were identified. Then, the structural and morphological evolution of low-temperature GaN nucleation layers were examined at the observed temperature domains of nitridation. Subsequently, a series of experiments were performed to study the influence of Ga and N precursor flow rates and epilayer growth temperature on the surface evolution of N-polar GaN. The observed results were analyzed in terms of thermodynamic and kinetic parameters of GaN growth. This work reports high-surface quality N-polar GaN epilayers without surface hillocks, exhibiting surface roughness about 1.5 nm over 2 × 2 μ m 2 area and with good crystalline quality on nominally on-axis c-plane sapphire substrates at low epilayer growth temperatures. [ABSTRACT FROM AUTHOR]

In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures. [ABSTRACT FROM AUTHOR]

The epitaxial growth of semiconductors is a very important step for the processing of microelectronic devices. Solid Phase Epitaxial Regrowth (SPER) is involved in both the recrystallization of amorphous silicon and germanium areas. Selective epitaxial growth (SEG) is routinely used in manufacturing modern 3D devices like finFETs, raised source/drain transistors, gate-all-around transistors, etc. In this work, lattice kinetic Monte Carlo modeling is used as the main tool for the modeling and simulation of epitaxial growth in IV and III–V based materials. This is done by detecting particular local configurations at the interfaces, and assigning local growth rates depending on such configurations. This simple idea is used to identify recrystallization planes or to compute different formation energies for the trapping, detrapping and migration of atoms. Introduction of defects is also possible by allowing the formation of twins and small defective areas. We will show different cases where our model is used, namely: SPER and defect formation of Si, and we will explain how the models can be extended to simulate the epitaxial growth of III–V materials and to obtain the different facet formation and growth kinetics. All these cases are compared with relevant experimental results from the literature to provide an assessment of their current capabilities but also possible limitations. [ABSTRACT FROM AUTHOR]

Being an attractive and demanding candidate in the field of energy conversion, germanium has attained widespread applications. The present work is aimed at the study of metal organic vapour phase epitaxy of germanium thin films on (0 0 1) silicon at different growth temperatures using isobutyl germane as a precursor. The epilayers were characterized by X-ray diffraction, high resolution transmission electron microscopy, atomic force microscopy and scanning electron microscopy in order to understand the structural and morphological properties. The films were found to be epitaxially grown and single crystalline with slight misorientation (below 0.1 degrees). The interface between the film and substrate was analyzed in depth and different temperature dependent growth behaviours were evidenced. The major relevant lattice imperfections observed were attributed to planar defects and threading dislocations. [ABSTRACT FROM AUTHOR]

Recently, pulsed laser deposition (PLD) technology makes viable the epitaxial growth of group III-nitrides on thermally active substrates at low temperature. The precursors generated from the pulsed laser ablating the target has enough kinetic energy when arriving at substrates, thereby effectively suppressing the interfacial reactions between the epitaxial films and the substrates, and eventually makes the film growth at low temperature possible. So far, high-quality group III-nitride epitaxial films have been successfully grown on a variety of thermally active substrates by PLD. By combining PLD with other technologies such as laser rastering technique, molecular beam epitaxy (MBE), and metal-organic chemical vapor deposition (MOCVD), III-nitride-based light-emitting diode (LED) structures have been realized on different thermally active substrates, with high-performance LED devices being demonstrated. This review focuses on the epitaxial growth of group III-nitrides on thermally active substrates by PLD and their use in the development of LED devices. The surface morphology, interfacial property between film and substrate, and crystalline quality of as-grown group III-nitride films by PLD, are systematically reviewed. The corresponding solutions for film homogeneity on large size substrates, defect control, and InGaN films growth by PLD are also discussed in depth, together with introductions to some newly developed technologies for PLD in order to realize LED structures, which provides great opportunities for commercialization of LEDs on thermally active substrates. [ABSTRACT FROM AUTHOR]

We report the selective area growth of GaAs in V-shaped trenches on Si (001) substrates via metal-organic chemical vapor deposition (MOCVD). High quality GaAs thin films were achieved using a two-step growth process and the aspect ratio trapping method. The evolution of GaAs growth in V-shaped trenches was investigated at all its stages, nucleation layer growth, crystallization, and top layer growth, with the help of in situ normal incidence reflectance measurements. A schematic growth mode was proposed and verified by scanning electron microscope (SEM). We also investigated the impact of nucleation layer thickness and reactor pressure on the crystal quality of GaAs selectively grown on Si through high resolution X-ray diffraction (HRXRD) measurements. [ABSTRACT FROM AUTHOR]

We demonstrate an atomic force microscopy based method for estimation of defect density by identification of threading dislocations on a non-flat surface resulting from metamorphic growth. The discussed technique can be applied as an everyday evaluation tool for the quality of epitaxial structures and allow for cost reduction, as it lessens the amount of the transmission electron microscopy analysis required at the early stages of projects. Metamorphic structures with low surface defectivities (below 10 6 ) were developed successfully with the application of the technique, proving its usefulness in process optimisation. [ABSTRACT FROM AUTHOR]

We have studied the mechanism of pulsed NH 3 growth in metalorganic chemical vapor deposition by investigating the influence of interruption duration of NH 3 , growth temperature, pressure and NH 3 flow rate on the growth behavior of GaN selective area growth (SAG). The essential mechanism of pulsed NH 3 is to create a short-term metal-rich growth condition, thus facilitating the growth of { 1 0 1 ¯ 1 } facets. Optimized pulse duration, growth temperature, pressure and NH 3 flow rate balance the amount of Ga atoms on the surface and create an appropriate metal-rich condition, resulting in an enhanced lateral growth rate by dramatically increasing the growth rate of { 1 0 1 ¯ 1 } facet. We have achieved hexagonal GaN plates with flat c -plane top surfaces and { 1 0 1 ¯ 0 } vertical sidewalls on substrates with a fill factor of about 0.1%. The understanding of pulsed NH 3 growth technique will significantly promote the preparation of crystals by SAG or epitaxial lateral overgrowth, especially on substrates with a very low fill factor. [ABSTRACT FROM AUTHOR]

The use of graphene as a template layer for the heteroepitaxy of III-nitrides (GaN and AlN) has gained interest due to the hexagonal arrangement of the sp 2 hybridized carbon atoms being similar to the (0001) c-plane of wurtzite GaN. In this study, the nucleation of GaN and AlN by metalorganic chemical vapor deposition on quasi-free standing epitaxial graphene (EG) was investigated. We observed that the nucleation of AlN and GaN was preferential along the periodic (1 1 ¯ 0 n ) EG coated step edges and at defects sites on the (0001) terraces due to the enhanced chemical reactivity at those regions. The density of nuclei on the (0001) terraces of EG increased with the incorporation of nitrogen defects into the graphene lattice via NH 3 exposure as was evident from surface chemical analysis by XPS. Raman spectral mapping showed that GaN selectively nucleates on regions of few-layered EG as opposed to regions of multi-layered EG. HR-TEM also revealed that the EG underlayers were highly defective in the region of GaN nucleation, however, the GaN nuclei were single crystalline, c-axis oriented and were free of threading dislocations. In contrast, polycrystalline islands of AlN were found to nucleate on EG without producing disorder in the underlying EG. [ABSTRACT FROM AUTHOR]

MOCVD has been associated with batch processing of III–V opto-electronic devices for decades, with epitaxial structures deposited on up to 200 mm diameter wafers. Recent development in thin film PV has seen the gap in conversion efficiencies closing in on that of the commonly found multicrystalline Si wafer based PV. To further improve the conversion efficiency of thin film PV towards the theoretical limits of single junction solar cells requires a technique such as MOCVD with scalability potential. Preliminary results on the development of a chamberless inline process are reported for up to 15 cm wide float glass, progressively coating each layer in the CdTe solar cell as the heated substrate passes under each coating head in turn and entirely at atmospheric pressure. Emphasis is made on ensuring that the chamberless coating heads can be operated safely using a combination of nitrogen curtain flows and a balanced exhaust pressure system. Results are also presented on the exclusion of oxygen and moisture from the coating area, achieved using the same gas flow isolation process. This paper also reviews the achievements made to-date in the transfer of the high efficiency batch MOCVD produced CdTe solar cell to the chamberless inline process demonstrating device quality thin films deposition. [ABSTRACT FROM AUTHOR]

Indium phosphide and silicon play important and complementary roles in communications wavelength photonic devices. Realizing high quality coalesced epitaxial lateral overgrown (ELO) InP films on Si could greatly reduce cost and encourage the proliferation of energy efficient photonic integrated circuits in consumer devices. By adjusting a parallel line ELO mask and metalorganic vapor phase epitaxial growth conditions, we have fully coalesced and partially coalesced epitaxial lateral overgrowth of InP on InP substrates and Si substrates having strain relaxed III/V buffer layers, respectively. Extended defects were investigated using transmission electron microscopy and were not found to originate at the coalescence of the nearest neighbor growth fronts for linear parallel growth windows oriented 60° off of [0-11] when using a high V/III ratio of 406. In addition, narrowly separated linear parallel growth windows having a large aspect ratio of 7.5 were seen to inhibit the upward propagation of stacking faults through several neighboring openings. Elimination of these two defect sources would leave primarily the challenge of optimizing the morphology of the overgrown InP as a substantial barrier to achieving coalesced ELO InP of sufficient quality for photonic device applications. [ABSTRACT FROM AUTHOR]

We investigated the effects of antimony (Sb) overpressure during thermal cleaning (TC) on the surface morphology of InSb substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). During the TC process under H2 ambient, indium (In) droplets were observed inside etch pits on InSb(001) surfaces due to the Sb evaporation from InSb substrates. On the other hand, when InSb substrates were thermally cleaned under trimethylantimony (TMSb) ambient, the formation of In droplets and the etch pits were suppressed, resulting in the smooth InSb surface. The surface morphology of InSb was dependent on TC temperature. Rough surface morphology was observed at low TC temperature of 435 °C and it became smoother with increasing TC temperature. The improvement of surface morphology was caused by the surface stabilization with increasing Sb flux and the increase of adatom migration. The dependence of TMSb flow rate on the surface morphology was also investigated. The TMSb overpressure during the TC of InSb must be maintained to grow high quality InSb epitaxial layers with smooth surface using MOCVD. [ABSTRACT FROM AUTHOR]

Abstract: Efficient photoluminescence (PL) spectra from GaN and InGaN layers at temperatures up to 1100K are observed with low noise floor and high dynamic resolution. A number of detailed spectral features in the PL can be directly linked to physical properties of the epitaxial grown layer. The method is suggested as an in situ monitoring tool during epitaxy of nitride LED and laser structures. Layer properties like thickness, band gap or film temperature distribution are feasible. [Copyright &y& Elsevier]

Abstract: We report about a MOVPE parameter study carried out on a Planetary Reactor to determine factors that govern the incorporation efficiency of aluminum and gallium into Al x Ga1−x N, hence its solid composition x and growth rate. Parameter variations include pressure, flow rate, wafer and ceiling temperature, V–III-ratio, and Al/(Al+Ga) inlet ratio. The target composition is 0.15

Abstract: Strain fields arising from a non-uniform distribution of misfit dislocations in an underlying compositionally graded buffer are shown to be sufficiently strong to modify indium incorporation in III-phosphide light emitting layers. Composition fluctuations (x In±0.02) in lattice-mismatched (Al y Ga1−y ) x In1−x P thin films with length-scales of 5–10μm and a broadened light emission spectra are observed. Cathodoluminescence, photoluminescence and wavelength dispersive x-ray spectroscopies are used in this analysis to generate spatial maps of luminescence spectra and element distributions in metal-organic chemical vapor deposition (MOCVD) grown films. It is seen that these fluctuations due to misfit dislocations are hard to eliminate via growth-kinetics alone but can be lowered through the use of miscut substrates or spacer layers between the graded buffer layer and the active layer. A link between crosshatch surface-roughness and group-III atom distribution under group-V rich growth conditions in both AlInP and GaInP films is also demonstrated. In summary, the interaction of the dislocation strain field with the growth surface can affect the optical characteristics of lattice-mismatched LEDs even if the final threading dislocation density is low. [Copyright &y& Elsevier]

Abstract: Gallium nitride (GaN) films have been grown by using our newly developed Radical-Enhanced Metalorganic Chemical Vapor Deposition (REMOCVD) system. This system has three features: (1) application of very high frequency (60MHz) power in order to increase the plasma density, (2) introduction of H2 gas together with N2 gas in the plasma discharge region to generate not only nitrogen radicals but also active NH x molecules, and (3) radical supply under remote plasma arrangement with suppression of charged ions and photons by employing a Faraday cage. Using this new system, we have studied the effect of the trimethylgallium (TMG) source flow rate and of the plasma generation power on the GaN crystal quality by using scanning electron microscopy (SEM) and double crystal X-ray diffraction (XRD). We found that this REMOCVD allowed the growth of epitaxial GaN films of the wurtzite structure of (0001) orientation on sapphire substrates with a high growth rate of 0.42μm/h at a low temperature of 800°C. The present REMOCVD is a promising method for GaN growth at relatively low temperature and without using costly ammonia gas. [Copyright &y& Elsevier]

Abstract: A mathematical model was developed to examine the growth rate of III–V compounds inside sub-micron trenches by MOVPE. Based on this model, we theoretically analyzed the possible dependence of the growth rate on the trench width primarily from two aspects, i.e. Knudson diffusion and enhanced equilibrium vapor pressure due to the shrinking trench size. Then, associated with the experimental data from the growth of both InAlAs and InAs, we found that the average growth rate inside submicron trenches is primarily influenced by trench diffusion type under typical growth conditions. [Copyright &y& Elsevier]