Organic Chemical Vapor Deposition Growth Research Articles

Hexagonal-based pyramid void defects in GaN and InGaN

We report a void defect in gallium nitride (GaN) and InGaN, revealed by aberration-corrected scanning transmission electron microscopy (STEM). The voids are pyramids with symmetric hexagonal {0001} base facets and {101¯1} side facets. Each pyramid void has a dislocation at the peak of the pyramid, which continues up along the [0001] growth direction to the surface. Some of the dislocations are hexagonal open core screw dislocations with {101¯0} side facets, varying lateral widths, and varying degrees of hexagonal symmetry. STEM electron energy loss spectroscopy spectrum imaging showed a large C concentration inside the void and on the void surfaces. There is also a larger C concentration in the GaN (or InGaN) below the void than above the void. We propose that inadvertent carbon deposition during metal organic chemical vapor deposition growth acts as a mask, stopping the GaN deposition locally, which in combination with lateral overgrowth, creates a void. Subsequent layers of GaN deposited around the C covered region create the overhanging {101¯1} facets, and the meeting of the six {101¯1} facets at the pyramid’s peak is not perfect, resulting in a dislocation.

Nucleation of ReBa2Cu3Ox(Re = rare-earth) during high-rate metal-organic chemical vapor deposition growth

Large-scale, high-rate epitaxial growth technology for the second-generation superconducting wire brings unique technological challenges for the thin-film coating industry. One of the most difficult steps of the process is controlling nucleation of a complex compound over a km-long low-cost oxide template. Here, we analyze early stages of industrial-scale epitaxial metal organic chemical vapor deposition (MOCVD) growth of ReBa2Cu3Ox (REBCO, Re = rare-earth) on buffered metal substrates. The nucleation event is detected by high-flux synchrotron X-ray diffraction and confirmed by atomic force microscopy. REBCO nuclei exhibit a strong preference for edges of the buffer grain, indicating that (001) steps of the buffer grains are preferred nucleation sites. It is concluded that random nucleation of REBCO is caused by agglomerates of small buffer grains.

Catastrophic-Optical-Damage-Free InGaN Laser Diodes With Epitaxially Formed Window Structure

High-power InGaN-based laser diodes (LDs) are expected as light-sources of various high-power applications. The catastrophic-optical-damage (COD) is a major failure mechanism to limit the output power, where optical absorption at a light-emitting facet causes an irreversible damage to the LDs. In this paper, a window structure in InGaN-based LDs to suppress the COD is demonstrated for the first time. The structure is formed by the metal organic chemical vapor deposition growth over a recess placed besides of the ridge-waveguide. The In composition in the quantum well which is corresponding to the bandgap energy is reduced by controlling the local tilt angle at the sidewall of the recess. Thus, the formed window structure eliminates undesired optical absorption at the cleaved facet so that extremely high light output power over 2 W in narrow-stripe ridge-waveguide InGaN-based blue-violet LDs is achieved without any CODs.

BST FILMS GROWN BY METAL ORGANIC CHEMICAL VAPOR DEPOSITION INCORPORATING REAL-TIME CONTROL OF STOICHIOMETRY

ABSTRACT We present preliminary results of metal organic chemical vapor deposition (MOCVD) growth of BaxSr1-xTiO3 (BST) thin films. Films were deposited on MgO, sapphire, Si, and Si/Pt/Ti substrates. Real-time monitoring of the precursor flux by UV absorption spectroscopy was used to control the composition of the films over the range 30 ≤ x ≤ 80. The films were characterized for a number of attributes including composition, crystalline structure, and morphology.

Computational and experimental studies on the growth of nonpolar surfaces of gallium nitride

Surface diffusion of the adatoms strongly influences the surface morphology of thin films. We have carried out density functional theory calculations to study the binding energies, migration pathways, and diffusion barriers for adatoms such as Ga and N on the nonpolar surface such as m- and a-plane GaN surfaces and compare it with the results on c-plane GaN surfaces. A strong anisotropy was observed for the diffusion behavior for Ga adatom on m- and a-plane GaN surfaces with the channels of low diffusion barrier in a- and c-crystallographic directions, respectively. The experimental observation during the metal organic chemical vapor deposition growth of m- and a-plane GaN surfaces show striated surface morphology with the steps oriented in a- and c-crystallographic directions, respectively.

Influence of the Density of Crack-Initiating Defects on Crack Spacing for GaN Films on Si(111) Substrate

This study examines the cracking of GaN films grown on Si(111) substrates, with particular focus on the effect of the density of crack-initiating defects (CIDs) on the crack spacing. The relationship between the CID density and crack spacing was examined by comparing specimens of the same thickness and under the same stress but with different CID density. The CID density in the GaN layer was changed by varying the ion-implanted area using patterning prior to metal–organic chemical vapor deposition (MOCVD) growth. The crack spacing decreased with increasing CID density, but this effect could not be explained by the previous model. Therefore, a CID-density related factor, nd, was newly introduced to explain the crack spacing and film stress relationship.

Metal–Organic Chemical Vapor Deposition Growth and Characterization of InAlGaN Multiple Quantum Wells

InAlGaN multiple quantum wells (MQWs) have been characterized for the development of ultraviolet light emitting diodes. Epilayers were grown on sapphire substrates by a metal–organic chemical vapor deposition. Temperature-dependent photoluminescence (PL) measurements were carried out for MQWs with different well-layer thicknesses. For MQWs with 2-nm-thick well layers, the emission intensity at room temperature and the internal quantum efficiency were higher than those of other MQWs. Furthermore, the localization effect in MQWs could be confirmed for well layers of more than 2 nm thickness because the PL peak energy exhibited S-shaped behavior. We have successfully fabricated high-performance InAlGaN MQWs.

Manipulation of Room Temperature Ferromagnetic behavior of GaMnN Epilayers

AbstractWe report on metal organic chemical vapor deposition growth of GaMnN/p-GaN/n-GaN multilayer structures and manipulation of room temperature (RT) ferromagnetism (FM) in a GaMnN layer. The GaMnN layer was grown on top of a n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. Ms was almost doubled after annealing demonstrating that the FM observed in GaMnN film is carrier-mediated. To control the hole concentration of the p-GaN layer by depletion, GaMnN/p-GaN/n-GaN multilayer structures of different p-GaN thickness (Xp) were grown on sapphire substrates. We have demonstrated that the FM depends on the Xp and the applied bias to the GaN p-n junction. The FM of these multilayer is independent on the top GaMnN layer thickness (tGaMnN) for tGaMnN >200 nm and decreases for tGaMnN < 200 nm. Thus the room temperature FM of GaMnN i-p-n structure can also be controlled by changing Xp and tGaMnN in the GaMnN i-p-n structures.

Microstructure and luminescent properties of novel InGaP alloys on relaxed GaAsP substrates

We present a metal organic chemical vapor deposition (MOCVD) growth study of unconventional alloys of InGaP (with In fraction of 0.2–0.4) grown on fully relaxed GaAsP virtual substrates for the application of high performance visible light emitting diodes (LEDs) and lasers in the green to red range of the visible spectrum. Several defects which are harmful to optical performance were identified, characterized, and removed. These include CuPt–B order (which lowers band gap), phase separation or short range order (which contributes to leakage currents and reduces luminescence) and undulation of the virtual substrate surface (which prevents high quality epitaxial growth). Each of these defects is understood through a two-step growth model which describes the formation and subsequent randomization of defects during growth. Through control of MOCVD parameters including growth temperature, V/III ratio, growth rate, and surfactant we demonstrate growth of extremely high quality InGaP heterostructures which hold promise for fabrication of light emitting devices.

Kinetic Monte Carlo study of metal organic chemical vapor deposition growth dynamics of GaN thin film at microscopic level

Group III nitrides, especially gallium nitride (GaN), have many applications. The materials are usually grown by metal organic chemical vapor deposition (MOCVD) technology. By combining the computational fluid dynamics and kinetic Monte Carlo method, we present a multiscale modeling of fluid dynamics, thermodynamics, and molecular dynamics to study the chemical and physical growth process of GaN in a standard MOCVD reactor, which shows a general agreement with experimental results. The theoretical model thus provides us with a fundamental guideline for optimizing GaN MOCVD growth at the microscopic level.

Influence of the AlN interlayer crystal quality on the strain evolution of GaN layer grown on Si (111)

The strain evolution in metal organic chemical vapor deposition growth of GaN on Si (111) substrate with an AlN interlayer is studied. During the growth of GaN film on AlN interlayer, the growth stress changes from compression to tension. The study shows that the density of V trenches in the AlN interlayer surface and the threading dislocations generated in the AlN interlayer have a significant influence on this strain evolution process. The dislocations generated in AlN interlayer may thread across the interface and play a key role in the strain evolution process of the GaN layer grown on AlN interlayer.

Interfacial reaction during MOCVD growth revealed by in situ ARXPS

AbstractAngle‐resolved X‐ray photoelectron spectroscopy (ARXPS) experiments were performed to study in situ the reaction at the film–substrate interface during metal organic chemical vapor deposition (MOCVD) growth of TiO2 thin films deposited on the silicon substrate. The in‐depth distribution of chemical species was determined using several ARXPS thickness calculation models considering either single or bilayer systems. By the comparison of two single‐layer models, the presence of a second layer composed of silicon oxide was evidenced. High‐resolution transmission electron microscopy (HRTEM) observations confirmed the stratification of the film in two layers, as well as the perfect wetting of the surface by TiO2, irrespective of the model used. The contribution of the ARXPS bilayer model was demonstrated by the agreement of the values of film thickness obtained by both techniques. Nevertheless, the correlation between each layer's thickness was only possible by taking into account chemical species mixing. Indeed, the presence of oxidised silicon in the upper TiO2 layer, in addition to that of the SiOx interlayer, has to be considered to interpret ARXPS results in a correct way. Copyright © 2006 John Wiley & Sons, Ltd.

UHV-MOCVD growth of TiO 2 on SiO x/Si(1 1 1): Interfacial properties reflected in the Si 2p photoemission spectra

Metal–organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 °C and flux-limited growth at 500 °C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiO x /Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiO x /Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO 2) x (SiO 2) y where x and y changes linearly and continuously over the interface. The model quantifies how (TiO 2) x (SiO 2) y mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon.

Monolithically integrated InP-based photonic chip development for O-CDMA systems

This work discusses photonic integration efforts toward developing an InP-based monolithically integrated photonic chip for optical code-division multiple-access (O-CDMA) system applications. The chip design includes the colliding pulsed mode (CPM) locked laser, the Mach-Zehnder interferometer-based threshold detector (MZI), and the monolithic O-CDMA encoder/decoder chip based on array-waveguide-gratings and phase modulator arrays. The compact 4 /spl times/ 1 cm monolithic chip can replace a complex and large O-CDMA setup based on bulk optics. The integration technique involves active-passive integration using dry etching, metal organic chemical vapor deposition growth, and lateral hydride vapor phase epitaxy regrowth technologies. The fabricated CPM showed stable 1.54 ps modelocked laser output, the MZI showed excellent O-CDMA threshold detection, and the O-CDMA encoder showed Walsh-code O-CDMA encoding. Further, the fabricated devices showed excellent planarity, which accelerate our progress toward monolithic integration of O-CDMA systems.

Intrinsic stresses in AlN layers grown by metal organic chemical vapor deposition on (0001) sapphire and (111) Si substrates

Stress evolution during metal organic chemical vapor deposition growth of AlN layers on (111) Si and (0001) sapphire substrates was investigated using in situ wafer curvature measurements in order to understand the origin of growth stresses. AlN layers 170±30nm thick were deposited over a temperature range of 600–1100°C at a growth rate of 0.2±0.05nm∕s. On (111) Si, AlN films grow under a constant tensile stress right from the beginning of growth in the temperature range investigated. In contrast, above 900°C on sapphire, an initial compressive growth stress is observed followed by a transition to a final tensile stress, while below 800°C the stress is tensile right from the beginning of growth as observed on Si. The origin of this stress behavior is explained in terms of a combination of epitaxial stress and grain coalescence stress. Calculation of the grain coalescence stresses show that the value is higher for growth on sapphire substrates than on Si substrates. Also, for growth on both substrates, a sharp drop in the value of the coalescence related tensile stress is observed between 900°C and 800°C. Both these features are correlated to the variation in the integral breadth of the (0002) and (101¯1) AlN x-ray rocking curves. It is shown that both the lower tensile stress on Si substrates and the drop in stress between 800°C and 900°C can be attributed to the reduction in grain coalescence stresses due to increasing grain boundary energies in the film resulting from increasing grain misorientation with respect to the substrate/film interface.

A Nucleation Study of GaN Multifunctional Nanostructures

ABSTRACTThis paper reports the Metal Organic Chemical Vapor Deposition (MOCVD) growth of GaN nanostructures. The use of MOCVD allows the direct integration of these nanostructures into pre-existing device technology. The formation of GaN nanostructures grown on AlN epitaxial layers were studied as a function of growth temperature, growth rate, V-III ratio and the amount of deposited material. A wide range of temperatures from 800 °C to 1100 °C and V-III ratios from 30 to 3500 were applied to determine the optimal growth conditions for nucleation studies in a modified production reactor. Small GaN nanostructures with lateral dimensions below 50 nm and low aspect ratios were obtained using relatively low temperatures of 815 °C and extreme metal-rich growth conditions. Island densities up to 1010cm−2were achieved using silane as an anti-surfactant to increase the available nucleation sites. Manganese has been incorporated into these nanostructures to enhance the multifunctional ferromagnetic properties of GaMnN.

MOCVD growth of AlN/GaN DBR structures under various ambient conditions

The high-reflectivity AlN/GaN distributed Bragg reflector (DBR) structures were realized by metal organic chemical vapor deposition (MOCVD) growth under pure N 2 ambient for AlN epilayer growth. The highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442 nm was obtained. For the DBR structure with AlN layer grown under mixture of N 2/H 2 and pure H 2 conditions, the center wavelength was blue-shifted to 418 and 371 nm and the peak reflectivity also showed a reduction to 92% and 79%, respectively. The stopband width also decreases with increasing H 2 contents. The surface roughness and the grain size of the grown DBR structures showed an increase with increasing the H 2 ambient gas ratio. For realization of a high reflectivity and broad bandwidth of AlN/GaN DBR by using the MOCVD growth method, the pure N 2 ambient gas for growth of AlN layer should be preferable and optimal condition.

Metal organic chemical vapor deposition growth of epitaxial SrRuO 3 and CaRuO 3 thin films with different orientations as the bottom electrode for epitaxial ferroelectric thin film

70 nm-thick (1 0 0)c, (1 1 0)c and (1 1 1)c-oriented epitaxial SrRuO 3 and CaRuO 3 thin films were grown on (1 0 0), (1 1 0) and (1 1 1)SrTiO 3 substrates, respectively, by metal organic chemical vapor deposition (MOCVD) at 750°C. Thickness fringes were observed for the (1 0 0)c- and (1 1 0)c-oriented SrRuO 3 films, suggesting a smooth surface for the film and the film-substrate interface. (1 1 1)c-oriented SrRuO 3 and CaRuO 3 films showed a rough surface compared to the (1 0 0)c- and (1 1 0)c-oriented films. Resistivity was independent of the film orientation. These films are useful as bottom electrodes for epitaxial ferroelectric thin films.

Metal–organic chemical vapor deposition growth of GaN thin film on 3C-SiC/Si(111) substrate using various buffer layers

GaN films were grown on 3C-SiC/Si(111) substrate using GaN, AlN, and GaN/AlN superlattices as the buffer layer in a metal–organic chemical vapor deposition (MOCVD) system. The surface morphology and structural and optical qualities of the GaN films were greatly improved by employing the buffer layers in the growth of GaN film on the 3C-SiC/Si substrate. The use of the superlattice buffer layer produced well-oriented GaN growth along the c-axis with good surface morphology. Low-temperature photoluminescence (PL) measurements showed that peaks associated with band-edge emission and donor–accepter pair recombination (D 0A 0) were observed from GaN films grown with and without GaN or AlN buffer layers, whereas GaN films grown with the superlattice buffer layer exhibited a strong band-edge peak with very weak D 0A 0 emission. The surface morphology and structural and optical properties of the GaN films were well correlated for the evaluation of GaN crystal quality.

Asymmetric output characteristics in 1.3-μm spot-size converted laser diodes

A spot-size converted laser diode (SSC-LD) with a vertically tapered passive waveguide structure was fabricated by butt-joint-built-in (BJB) coupling and selective area metal organic chemical vapor deposition growth. A high coupling efficiency exceeding 50% and 1-dB alignment tolerance of /spl plusmn/2.5 /spl mu/m were obtained at a distance of 20 /spl mu/m between a flat-end single-mode fiber and the SSC-LD. Experimental results show that the asymmetric output property can be described by the radiation mode added to the guide mode and spatial hole-burning in the active region.