Low-pressure Metalorganic Chemical Vapor Research Articles

Supported MOCVD TiO2 Thin Films Grown on Modified Stainless Steel Mesh for Sensing Applications.

Among semiconductor metal oxides, that are an important class of sensing materials, titanium dioxide (TiO2) thin films are widely employed as sensors because of their high chemical and mechanical stability in harsh environments, non-toxicity, eco-compatibility, and photocatalytic properties. TiO2-based chemical oxygen demand (COD) sensors exploit the photocatalytic properties of TiO2 in inducing the oxidation of organic compounds to CO2. In this work, we discuss nanostructured TiO2 thin films grown via low-pressure metal organic chemical vapor deposition (MOCVD) on metallic AISI 316 mesh. To increase the surface sensing area, different inorganic acid-based chemical etching protocols have been developed, determining the optimal experimental conditions for adequate substrate roughness. Both chemically etched pristine meshes and the MOCVD-coated ones have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) microanalysis, and X-ray photoelectron spectroscopy (XPS). We demonstrate that etching by HCl/H2SO4 at 55 °C provides the most suitable surface morphology. To investigate the behavior of the developed high surface area TiO2 thin films as COD sensors, photocatalytic degradation of functional model pollutants based on ISO 10678:2010 has been tested, showing for the best performing acid-etched mesh coated with polycrystalline TiO2 an increase of 60% in activity, and degrading 66 µmol of MB per square meter per hour.

Effects of Buffer Layer on Structural Properties of Nonpolar (112¯0)-Plane GaN Film

Nonpolar (112¯0) a-plane GaN films were grown on semipolar (11¯02) r-plane sapphire substrates using various buffer layers within a low-pressure metal organic chemical vapor deposition system. The structural properties of nonpolar a-plane GaN films were intensively investigated by X-ray diffraction and Raman spectra measurements. A set of buffer layers were adopted from a GaN layer to a composite layer containing a multiple AlN layers and a gradually varied-Al-content AlGaN layer, the full width at half maximum of the X-ray rocking curves measured along the [0001] and [101¯0] directions of a-plane GaN were reduced by 35% and 37%, respectively. It was also found that the basal-plane stacking faults (BSFs) density can be effectively reduced by the heterogeneous interface introduced together with the composite buffer layer. An order of magnitude reduction in BSFs density, as low as 2.95 × 104 cm−1, and a pit-free surface morphology were achieved for the a-plane GaN film grown with the composite buffer layer, which is promising for the development of nonpolar GaN-based devices in the future.

Scalable growth of atomically thin MoS2 layers in a conventional MOCVD system using molybdenum dichloride dioxide as the molybdenum source

To bring atomically thin transition metal dichalcogenides (TMDs) to practical application, a highly reproducible process to grow them over a large scale is indispensable. Here, we develop a carbon-free reproducible route for the scalable growth of high-quality monolayer MoS2 by selecting molybdenum dichloride dioxide (MoO2Cl2) as the Mo source and integrating the precursor with a standard low-pressure cold-wall metalorganic chemical vapor deposition (MOCVD) system. Specifically, combined with H2S as the sulfur source and using catalytic Dragontrail glass (DT-glass) as the main substrate, we investigate the effect of MoO2Cl2 flux, temperature, and deposition time on the growth, confirming MoO2Cl2 with reasonably high vapor pressure is well compatible with the MOCVD system that enables precise control of sources for uniform nucleation and growth of MoS2 over a large area. We successfully demonstrate the growth of carbon-free MoS2 monolayers on DT-glass with decent crystalline, optical, and electrical properties. Additionally, the initial attempts also manifest that the proposed strategy could be generalized for growing ultrathin MoS2 on other technologically important substrates, such as SiO2/Si and quartz, exhibiting superior optical quality and wafer-scale uniformity. This work provides a new avenue for the large-scale production of high-quality MoS2 monolayers and facilitates their use in practical applications.

Effect of different substrates on material properties of cubic GaN thin films grown by LP-MOCVD method

The III-nitride cubic phase are promising materials in photovoltaics and other optoelectronic devices due to their favorable material properties. This research work presents the growth of cubic gallium nitride (c-GaN) thin films on two different substrate gallium phosphide (GaP) and gallium arsenide (GaAs) substrates using the low-pressure metal–organic chemical vapor deposition (LP-MOCVD) technique. The growth conditions are modified for each substrate to obtain c-GaN epitaxial films with good crystalline quality. Stress values for c-GaN epitaxial layers 0.62 GPa and 1.24 GPa were calculated using X-ray diffraction measurements for c-GaN grown on GaP and GaAs substrates, respectively. The stress state calculated by XRD proved that in both cases, c-GaN on GaP and on GaAs substrates, they was compressed layers. Raman measurements showed two peaks for c-GaN at 555 cm−1 (TO) and 745 cm−1 (LO) modes for c-GaN grown on GaP. For GaAs, only observed 555 cm−1 (TO) mode. It obtained the formation of c-GaN epitaxial films on both substrates. The surface morphology and the quality of the films depend on the type of substrates, compact layers with better crystalline quality are observed in the samples grown in GaP than GaAs substrate. Band gap (Eg) of GaN was obtained with approximate values of 380 nm for c-GaN of both substrates, which is where the Eg of c-GaN is found.

Top-emitting 940-nm thin-film VCSELs transferred onto aluminum heatsinks

Thin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.

High‐pressure MOCVD growth of InGaN thick films toward the photovoltaic applications

The highly efficient photovoltaic cells require the In-rich InGaN film with a thickness more than 300 nm to achieve the effective photo⋅electricity energy conversion. However, the InGaN thick films suffer from poor crystalline quality and phase separations by using the conventional low-pressure metal organic chemical vapor deposition (MOCVD). We report on the growth of 0.3-1 μm-thick InGaN films with a specially designed vertical-type high-pressure MOCVD at the pressure up to 2.5 atms. The In incorporation is found to be greatly enhanced at the elevated pressures although the growth temperatures are the same. The phase separations are inhibited when the growth pressure is higher than atmospheric pressure, leading to the improved crystalline quality and better surface morphologies especially for the In-rich InGaN. The In0.4Ga0.6N with the thickness of 300 nm is further demonstrated as the active region of solar cells, and the widest photoresponse range from ultraviolet to more than 750 nm is achieved.

Ge Solar Cells with Micro-Rod Arrays: Structural and Optical Properties.

Ge single-junction solar cell structures are grown on micro-patterned Ge substrates using lowpressure metalorganic chemical vapor deposition. 300 nm high micro-rod arrays are formed on the p-Ge substrates using photolithography and dry etching techniques. The micro-rod arrays are designed with rod diameter varying from 5 to 15 μm and arranged in a hexagonal geometry with rod spacing varying from 2 to 12 μm. Ge p-n junction structures are fabricated by phosphorus atomic diffusion process on the micro-patterned Ge substrates. 100 nm thick InGaP window and 300 nm thick GaAs cap layers are grown to reduce the surface recombination and the ohmic contact resistivity, respectively. Our results indicate that the micro-rod structures improve the performance of the Ge solar cells. An improvement of 16.1% in the photocurrent of the Ge micro-rod solar cell is observed compared to that of a reference Ge solar cell with planar surface. The improvement in the short circuit current density can be attributed to the light trapping effect, enlarged p-n junction area, and enhanced carrier collection efficiency. As a result, the conversion efficiency of the Ge solar cell with micro-rod arrays (5 μm diameter, 2 μm spacing, and 300 nm height) is improved from 3.84 to 4.78% under 1 sun AM 1.5G conditions.

AlGaN/AlN/SiC Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors with Al2O3 Gate-Oxide and Step-Graded AlGaN Channel

Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs), grown on a SiC substrate, with step-graded Si-doped (n = 3 × 1018 cm-3) widegap AlxGa1-xN channel and Al2O3 gate-dielectric are investigated. Increased Al-compositions with x = 0.25, 0.5, and 0.75 towards the buffer were devised in the composite widegap channel. The high-k Al2O3 dielectric/passivation layer was grown by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. Experimental comparisons were made with respect to a conventional Schottky-gate HFET.The epitaxial structure of the studied Al2O3-dielectric Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN MOS-HFET (sample A) and Schottky-gate HFET (sample B). Both devices have the identical epitaxial structure grown on a SiC substrate by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The layer structure includes an undoped AlN buffer, a 20-nm undoped Al0.75Ga0.25N barrier, a 150-nm step-graded Si-doped (n = 3 × 1018 cm-3) AlxGa1-xN channel (x = 0.25, 0.5, and 0.75), and a 20-nm undoped Al0.75Ga0.25N barrier. Standard photolithography and lift-off techniques were used for device processing. For sample B, mesa etching was performed with respect to a 100-nm thick Ni barrier by using an inductively coupled-plasma reactive ion etcher (ICP-RIE). Flow rates were tuned and set at 10 sccm and 20 sccm for the mixed etching gases of BCl3 and Cl2, respectively. The 20-nm undoped Al0.75Ga0.25N barrier was etched away before deposition of source/drain electrodes. Ti (10 nm)/Al (50 nm)/Ni (10 nm)/Au (50 nm) were evaporated. The source/drain ohmic contacts were formed by annealing the sample for 25 seconds at 900°C by using a rapid thermal annealing (RTA) system (ULVAC MILA-5000). Then, 30-nm thick Al2O3 layer was deposited on the Al0.75Ga0.25N barrier by using the USPD technique. Finally, gate electrode of Ni (100 nm)/Au (50 nm) was evaporated after gate photolithography. As for sample A, the gate electrode was formed directly on the surface of Al0.75Ga0.25N barrier without oxide deposition.Improved device performance of the present MOS-HFET design have been obtained, including maximum drain-source current density (IDS, max ) of 130.1 A/mm at VGS = 10 V and VDS = 20 V, IDS at VGS = 0 V (IDSS0 ) of 83.1 mA/mm, on/off-current ratio (Ion /Ioff ) of 1.4 × 107, maximum extrinsic transconductance (gm, max ) of 11.8 mS/mm, two-terminal off-state gate-drain breakdown voltage (BVGD ) of -404 V, and three-terminal on-state drain-source breakdown voltage (BVDS ) of 364 V at 300 K. The present MOS-HFET design has also shown high spectral responsivity (SR) of 737 A/W under 250-nm deep-UV radiation at 300 K.

Improved Performance of Ge Solar Cell Using Graphene Quantum Dots.

We investigated the effect of graphene quantum dots (GQDs) on performance of single-junction Ge solar cell grown on (100) substrate by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Isobutylgermane (IBuGe) is used as a Ge precursor for the Ge solar cell growth. By employing GQDs, the power conversion efficiency of the Ge solar cell is improved up to 3.90% (Voc of 0.22 V, Jsc of 28.52 mA/cm², and FF of 63.83%) through effective photon management as compared to bare Ge solar cells of 3.24% under AM 1.5G illumination.

Effects of Thermal Annealing on Optical Properties of Be-Implanted GaN Thin Films by Spectroscopic Ellipsometry

Wide bandgap III-V compounds are the key materials for the fabrication of short-wavelength optical devices and have important applications in optical displays, optical storage devices and optical communication systems. Herein, the variable-angle spectroscopic ellipsometry (SE) measurements are performed to investigate the thickness and optical properties of beryllium-implanted gallium nitride thin films that have been deposited on (0001) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (LPMOCVD). The film layer details are described by using Parametric Semiconductor oscillators and Gaussian oscillators in the wavelength range of 200–1600 nm. The thickness, refractive indices and extinction coefficients of the Be-implanted films are determined at room temperature. Analysis of the absorption coefficient shows that the optical absorption edge of Be-implanted films changes from 3.328 eV to 3.083 eV in the temperature range of 300–850 K. With the variable temperature, Eg is demonstrated to follow the formula of Varshni. A dual-beam ultraviolet–visible spectrophotometer (UV–VIS) is used to study the crystal quality of samples, indicating that the quality of rapid thermal annealing (RTA) sample is better than that unannealed sample. By transport of ions in matter (TRIM) simulation and SE fitting the depths of Be implanted gallium nitride (GaN) films are estimated and in good agreement. The surface and cross-section morphologies are characterized by atomic force microscopy (AFM) and scanning electron microscope (SEM), respectively. The surface morphologies and thickness measurements of the samples show that RTA can improve crystal quality, while increasing the thickness of the surface roughness layer due to partial surface decomposition in the process of thermal annealing.

AlGaN-based UV-C distributed Bragg reflector with a λ-cavity designed for an external cavity structure electron-beam-pumped VCSEL

The external cavity structure electron-beam-pumped (EB-pumped) vertical cavity surface emitting laser (VCSEL) has an important demand for the distributed Bragg reflector (DBR) with an emission window at the working wavelength called λ-cavity. Herein, AlGaN-based UV-C band DBRs with λ-cavities around 280 nm are designed and investigated in detail, which have almost no been reported so far. The DBRs based on alternate stacked Al0.47Ga0.53N/AlN bilayers are in-situ grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Through a comprehensive protocol of structure optimization by theoretical simulation, epitaxial growth and in-depth characterization and analysis, a high-performance UV-C band DBR with a λ-cavity around 280 nm is successfully fabricated. The DBR presents a reflectivity as high as 81.3% at the λ-cavity, a maximum reflectivity of 89.8% at 282 nm and a stopband with a full-width at half-maximum (FWHM) of 24.7 nm, laying a foundation for developing the external cavity structure EB-pumped AlGaN-based UV-C VCSELs emerging as a promising alternative to the electrically pumped AlGaN-based UV-C lasers.

Assessment of synergistic effects of LP-MOCVD TiO2 and Ti surface finish for dental implant purposes

Three differently treated titanium substrates to be used in dental implant applications and with different surficial morphology were coated with titanium dioxide (TiO 2 ) films by using Low-Pressure Metal Organic Chemical Vapor Deposition (MOCVD). No literature references were found on the performance evaluation of the TiO 2 MOCVD coatings on substrates with different pristine morphology; in this work the influence of the pristine Ti surface characteristics on TiO 2 crystalline structure, morphology, wettability as well as on ion release, electrochemical behavior, tribocorrosion performance, and nano-mechanical properties were studied and discussed. It was shown that the pristine substrate influenced both the crystalline phases' formation and crystallite size. Scanning electron microscopy analyses and roughness evaluation showed the optimal conformal coverage of all the MOCVD coatings for all substrates, with grain size depending on the substrate morphology and topography. The wettability of the TiO 2 coated Ti substrates highlighted a superhydrophilic behavior and, if stored in air, decreased as a function of the time aging. Ions release tests, nanoindentation measurements, tribocorrosion, and potentiodynamic polarization experiments suggest the enhancement of functional properties of the coated samples. Titania sandblasted/acid etched coated Ti substrates generally showed the best performance of the functional properties for their use in dental implant fabrications. • TiO 2 coated samples allow better wettability in aqueous media. • Titania surface functionalization is a good strategy to reduce ion release. • Tribocorrosion studies indicate better behavior for TiO 2 coated samples. • TiO 2 surface functionalization improves the mechanical properties of bulk titanium.

Long time aging effect on Be-implanted GaN epitaxial layer

Be-implanted GaN thin films grown by low-pressure Metalorganic Chemical Vapor Deposition (LP-MOCVD), the postimplantation rapid thermal annealing (RTA) samples and the postimplantation RTA samples after 18 years’ room temperature (RT) aging were investigated by Resonant Raman scattering (RRS). It was observed that the Resonant Raman scattering intensity is most enhanced in the 4th order A1 (LO) mode in the after aging sample rather than both the 4th and 5th order A1(LO) mode at different temperatures in the postimplantation RTA sample, which is attributed to a different prominent laser excited emission involved in the RRS processes in the sample before and after aging. A jump step of the intensities of RRS modes was observed at 170 K. Based on the temperature dependent and power dependent RRS spectra, we estimate quantitatively the properties of the optical emission participated in RRS processes below and above this temperature, with the assumption that the intensity of the RRS modes is linearly proportional to the intensity of the optical emission involved in it. We obtained the activation energy of 65 meV and 85 meV for two emissions, respectively, and confirmed both emissions are not band edge related emission with power density dependent RRS spectra. We proposed the dominant optical emission changed from band edge emission to dopant related emission after aging. This study provides an evidence of evolution of optical properties and microstructures in postimplantation RTA GaN epilayers over long time RT aging, which could be a benefit to studying reliability control of devices based on this material.

Quantifying competitive grain overgrowth in polycrystalline ZnO thin films

The grain size evolution of polycrystalline thin films, which form by competitive grain overgrowth as commonly interpreted using the van der Drift model, is understood to follow a power-law scaling of the average grain size d with film thickness h, i.e. d ∝ hα. While simulations have identified a growth exponent α = 0.4 for three-dimensional growth, previous experimental studies did not confirm this value, instead finding α values in the range of ∼0.5–0.7. Here we study competitive grain overgrowth using a system of ZnO thin films grown by low-pressure metal–organic chemical vapor deposition. We present quantitative data on the evolution of grain size and orientation across the thickness of thin films, obtained by automated crystal orientation mapping of “double-wedge” transmission electron microscopy samples. The data from a-textured ZnO films, grown under three different conditions, are compared against van der Drift model predictions of self-similarity of the grain size distribution and the power-law scaling. The results are further interpreted by comparing to simulations of faceted polycrystalline film growth, which we adapt to the ZnO system by including idiomorphic growth shapes with a six-fold symmetry and random or biased nuclei orientations. As well as showing the predicted self-similarity of grain size distributions during growth, for the first time our experimental data confirm a power-law growth exponent of α = 0.4, as also predicted by the simulations using randomly oriented nuclei. Nevertheless, interpretation of this result is contingent on the absence of factors such as textured nucleation and renucleation during film growth. Indeed, only one film, grown at a higher ratio of H2O/DEZ precursor gases, displaying random initial nucleation, and minimal grain renucleation during growth, shows a proper conformance to the model nature and predictions.

Quantifying Competitive Grain Overgrowth in Polycrystalline ZnO Thin Films

The grain size evolution of polycrystalline thin films, which form by competitive grain overgrowth as commonly interpreted using the van der Drift model, is understood to follow a power-law scaling of the average grain size d with film thickness h, i.e. d ∝ hα. While simulations have identified a growth exponent α = 0.4 for three-dimensional growth, previous experimental studies did not confirm this value, instead finding α values in the range of ~0.5-0.7. Here we study competitive grain overgrowth using a system of ZnO thin films grown by low-pressure metal-organic chemical vapor deposition. We present quantitative grain data on the evolution of grain size and orientation across the thickness of thin films, obtained by automated crystal orientation mapping of double-wedge transmission electron microscopy samples. The data from a-textured ZnO films, grown under three different conditions, are compared against van der Drift model predictions of self-similarity of the grain size distribution and the power-law scaling. The results are further interpreted by comparing to simulations of facetted polycrystalline film growth, which we adapt to the ZnO system by including idiomorphic growth shapes with a six-fold symmetry and random or biased nuclei orientations. As well as showing the predicted self-similarity of grain size distributions during growth, for the first time our experimental data confirm a power-law growth exponent of α = 0.4, as also predicted by the simulations using randomly oriented nuclei. Nevertheless, interpretation of this result is contingent on the absence of factors such as textured nucleation and renucleation during film growth. Indeed, only one film, grown at a higher ratio of H2O/DEZ precursor gases, displaying random initial nucleation, and minimal grain renucleation during growth, shows a proper conformance to the model nature and predictions.

Исследование однородности состава по толщине слоев GaInAsP, полученных на подложках InP методом газофазной эпитаксии

GaInPAs/InP heterostructures grown by low pressure (0.1 bar, 600 oC) metal-organic chemical vapor phase deposition were investigated. The thicknesses of grown GaInAsP layers were about 1 µm. For the epitaxial layers Ga<sub>1-x</sub>In<sub>x</sub>P<sub>1-y</sub>As<sub>y)</sub> with average compositions of x = 0.77 – 0.87 and y = 0.07 – 0.42 the variation of V group elements content y with the epilayer depth were revealed, weher the compositions of V-group elements were changed up to Δy = 0.1 atomic fractions in V group elements sublattice. In most cases, y change occurs in a GaInAsP region up to 200 nm thick adjacent to the InP. In some cases, y changes throughout the whole GaInPAs layer thickness. Fo the epitaxial layers with a satisfactory crystal perfection the less was the mismatch between the substrate and the GaInPAs epitaxial layer, the smaller was the value of Δy. For GaInPAs layers characterized by a low degree of crystal perfection and a high lattice mismatch between GaInAsP and InP layers, the value of Δy was about zero. These data let us suggest that the incorporation of atoms of the V group in the epitaxial layer strongly depends on elastic deformation of the growing monolayer, that is mismatched with the underlying crystal surface.

Synchrotron Radiation X-Ray Absorption Spectroscopy and Spectroscopic Ellipsometry Studies of InSb Thin Films on GaAs Grown by Metalorganic Chemical Vapor Deposition

A series of ultrathin InSb films grown on GaAs by low-pressure metalorganic chemical vapor deposition with different V/III ratios were investigated thoroughly using spectroscopic ellipsometry (SE), X-ray diffraction, and synchrotron radiation X-ray absorption spectroscopy. The results predicted that InSb films on GaAs grown under too high or too low V/III ratios are with poor quality, while those grown with proper V/III ratios of 4.20–4.78 possess the high crystalline quality. The temperature-dependent SE (20–300°C) and simulation showed smooth variations of SE spectra, optical constants (n, k, e1, and ε2), and critical energy points (E1, E1+Δ1, E′0, E2, and E′1) for InSb film when temperature increased from 20°C to 250°C, while at 300°C, large changes appeared. Our study revealed the oxidation of about two atomic layers and the formation of an indium-oxide (InO) layer of ∼5.4 nm. This indicates the high temperature limitation for the use of InSb/GaAs materials, up to 250°C.

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate.

In0.82Ga0.18As epitaxial layers were grown on InP (100) substrates at 530 °C by a low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The effects of different buffer structures, such as a single buffer layer, compositionally graded buffer layers, and superlattice buffer layers, on the crystalline quality and property were investigated. Double-crystal X-ray diffraction (DC-XRD) measurement, Raman scattering spectrum, and Hall measurements were used to evaluate the crystalline quality and electrical property. Scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were used to characterize the surface morphology and microstructure, respectively. Compared with the In0.82Ga0.18As epitaxial layer directly grown on an InP substrate, the quality of the sample is not obviously improved by using a single In0.82Ga0.18As buffer layer. By introducing the graded InxGa1−xAs buffer layers, it was found that the dislocation density in the epitaxial layer significantly decreased and the surface quality improved remarkably. In addition, the number of dislocations in the epitaxial layer greatly decreased under the combined action of multi-potential wells and potential barriers by the introduction of a In0.82Ga0.18As/In0.82Al0.18As superlattice buffer. However, the surface subsequently roughened, which may be explained by surface undulation.

Free standing c-GaN films grown by low-pressure metalorganic chemical vapor deposition on GaP (100) substrates

Gallium nitride (GaN) films were synthesized by low pressure metalorganic chemical vapor deposition on GaP (100) substrates. Samples were grown using three-step growth method, which includes a) a nitridation process of the GaP surface, b) the growth of a GaN buffer layer and c) the growth of the high-temperature epilayer. X-ray diffraction, Raman spectroscopy and FESEM and HRTEM were used to study the changes in the surface, which suggests that the cubic phase nucleation takes place during nitridation process and remained at the top surface, which results in preferential growth of c-GaN.

Characterization of Gallium Indium Phosphide and Progress of Aluminum Gallium Indium Phosphide System Quantum-Well Laser Diode.

Highly ordered gallium indium phosphide layers with the low bandgap have been successfully grown on the (100) GaAs substrates, the misorientation toward [01−1] direction, using the low-pressure metal organic chemical vapor deposition method. It is found that the optical properties of the layers are same as those of the disordered ones, essentially different from the ordered ones having two orientations towards [1−11] and [11−1] directions grown on (100) gallium arsenide substrates, which were previously reported. The bandgap at 300 K is 1.791 eV. The value is the smallest ever reported, to our knowledge. The high performance transverse stabilized AlGaInP laser diodes with strain compensated quantum well structure, which is developed in 1992, have been successfully obtained by controlling the misorientation angle and directions of GaAs substrates. The structure is applied to quantum dots laser diodes. This paper also describes the development history of the quantum well and the quantum dots laser diodes, and their future prospects.