Organic Vapor Phase Epitaxy Growth Research Articles

Effect of step edges on the adsorption behavior on vicinal AlN(0001) surface during metal-organic vapor phase epitaxy: An ab initio study

We present systematic theoretical investigations for the adsorption behavior of Al and N adatoms on vicinal AlN(0001) surface under metal–organic vapor phase epitaxy (MOVPE) growth condition by means of ab initio electronic structure calculations. Prior to the investigation adatoms, we reveal the growth condition dependence of stable structure for bilayer step edges during the MOVPE. The vicinal surface with hydrogen terminated N atom and NH2 (N-H + Al-NH2) is found to be the most stable under N-rich limit whereas the surface with hydrogen terminated N atom (N-H + Al-H) with NH2 at the step edge is favorable over the wide range of Al chemical potential. This suggests that N-H + Al-NH2 and N-H + Al-H with NH2 at the step edge appear at high and low temperatures, respectively. For both surface models, we also elucidate that the adsorption energy of Al adatoms at the step edge is much lower than that in the terrace region, indicating that Al adatoms are easily incorporated into the step edge. The estimated values of Ehrlich-Schwöbel barrier (ESB) of Al adatoms for N-H + Al-NH2 and N-H + Al-H with NH2 at the step edge are −1.4 and −1.9 eV, respectively. The relationship between the adsorption behavior and surface morphology during the MOVPE is discussed on the basis of calculated ESB as well as adsorption energies and migration barriers.

MOVPE Growth of AlInP–InGaP Distributed Bragg Reflectors

This article discusses metal–organic vapor phase epitaxy growth of all-phosphide (AlInP–InGaP) distributed Bragg reflectors (DBRs) and their applications for thin flexible multijunction solar cell devices. DBRs with a peak reflectance of 884 nm—close to the GaAs bandgap energy—were grown. This all-phosphide DBR was monolithically integrated with a dual-junction (DJ) InGaP/GaAs solar cell. The DJ cell with a DBR exhibited a 3% increase in short-circuit current density ( J sc), in comparison with the DJ without a DBR. Both open-circuit voltage ( V oc) and fill factor ( FF) values of the solar cell did not change with the DBR integration.

Insight of surface treatments for CMOS compatibility of InAs nanowires

A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon by molecular beam epitaxy. The crucial step of this process is a new in-situ surface preparation under hydrogen (gas or plasma) during the substrate degassing combined with an in-situ arsenic annealing prior to growth. Morphological and structural characterizations of the InAs nanowires are presented and growth mechanisms are discussed in detail. The major influence of surface termination is exposed both experimentally and theoretically using statistics on ensemble of nanowires and density functional theory (DFT) calculations. The differences observed between Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) growth of InAs nanowires can be explained by these different surfaces terminations. The transition between a vapor solid (VS) and a vapor liquid solid (VLS) growth mechanism is presented. Optimized growth conditions lead to very high aspect ratio nanowires (up to 50 nm in diameter and 3 micron in length) without passing the 410 °C thermal limit, which makes the whole process CMOS compatible. Overall, our results suggest a new method for surface preparation and a possible tuning of the growth mechanism using different surface terminations.

Effect of growth temperature and V/III-ratio on the surface morphology of MOVPE-grown cubic zincblende GaN

The influence of growth temperature and V/III-ratio on the surface morphology of (001) cubic zincblende GaN epilayers during metal organic vapour phase epitaxy growth has been investigated using atomic force microscopy and transmission electron microscopy. The zincblende phase purity as determined by X-ray diffraction was found to be above 98% for most GaN epilayers studied. As the growth temperature was increased from 850 °C to 910 °C and as the V/III-ratio was separately increased from 38 to 300, surface features were found to be elongated in the [1-10] direction, and the ratio of the length to width of such surface features was found to increase. Faceting was observed at V/III-ratios below 38 and above 300, which in the latter case was accompanied by a reduction of the zincblende phase purity. An explanation for these morphological trends is proposed based on effects such as the reduced symmetry of the top monolayer of the (001)-oriented zincblende GaN lattice, diffusion of Ga and N adatoms on such a surface, and the relative energies of the crystal facets.

(Invited) First Principles and Themodynamical Studies on Matel Organic Vaper Phase Epitaxy of GaN

We analyzed metal organic vapor phase epitaxy growth mechanism of III-nitride semiconductors, GaN, AlN and InN based on first-principles calculations and thermodynamic analysis. With this calculated methods, we investigate the decomposition process of the group III source gases, X(CH3)3 (X = Ga, Al, In) at finite temperatures and whether the (CH3)2GaNH2 adduct can be formed or not. Our calculated results show that (CH3)2GaNH2 adduct cannot be formed in the gas phase reaction in GaN MOVPE. Whereas, (CH3)2AlNH2 adduct can be formed so much in gas phase in AlN MOVPE. In case of GaN MOVPE, trimethylgallium (TMG, [Ga(CH3)3]) almost decomposes into Ga gas on growth surface by the assistance of H2 carrier gas instead of (CH3)2GaNH2 adduct formation. Moreover, in case of InN MOVPE, (CH3)2InNH2 adduct formation cannot occur and it is relatively easy that In gas is produced even if there is no H2 carrier gas.

Thermodynamic considerations of the vapor phase reactions in III–nitride metal organic vapor phase epitaxy

We analyzed the metal organic vapor phase epitaxial growth mechanism of the III–nitride semiconductors GaN, AlN, and InN by first-principles calculations and thermodynamic analyses. In these analyses, we investigated the decomposition processes of the group III source gases X(CH3)3 (X = Ga, Al, In) at finite temperatures and determined whether the (CH3)2GaNH2 adduct can be formed or not. The results of our calculations show that the (CH3)2GaNH2 adduct cannot be formed in the gas phase in GaN metal organic vapor phase epitaxy (MOVPE), whereas, in AlN MOVPE, the formation of the (CH3)2AlNH2 adduct in the gas phase is exclusive. In the case of GaN MOVPE, trimethylgallium (TMG, [Ga(CH3)3]) decomposition into Ga gas on the growth surface with the assistance of H2 carrier gas, instead of the formation of the (CH3)2GaNH2 adduct, occurs almost exclusively. Moreover, in the case of InN MOVPE, the formation of the (CH3)2InNH2 adduct does not occur and it is relatively easy to produce In gas even without H2 in the carrier gas.

MOVPE growth of Ga(PBi) on GaP and GaP on Si with Bi fractions up to 8%

Dilute bismide containing materials can play an important role in addressing the issue of finding new highly efficient lasers for telecommunications as well as sensing applications. In the last several years a growing body of literature has emerged, particularly on the growth of Ga(AsBi). However, the metal organic vapor phase epitaxy growth of Ga(AsBi) with high amounts of Bi, which are necessary to overcome Auger recombination and reach telecommunications wavelengths, still remains a challenge. Ga(PBi) could be a promising alternative, but has not been deposited with significant amounts of Bi so far. A second argument for Ga(PBi) is that it could be grown on GaP, which was already deposited on Si. A number of researchers have reported theoretical calculations on the band structure of Ga(PBi), but experimental results are still lacking.In this work we present the first Ga(PBi) structures, grown by metal organic vapor phase epitaxy on GaP and on GaP on Si. By careful characterization with high resolution X-ray diffraction, atomic force microscopy, secondary ion mass spectrometry and scanning transmission electron microscopy, we will show that we have realized high quality Ga(PBi) with Bi fractions over 8%.

First-principles and thermodynamic analysis of trimethylgallium (TMG) decomposition during MOVPE growth of GaN

We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

Novel integration method for III–V semiconductor devices on silicon platform

A novel integration method for III–V semiconductor devices on a Si platform was demonstrated. Thin-film InP was directly bonded on a Si substrate and metal organic vapor phase epitaxy (MOVPE) growth was performed by using an InP/Si template. A void-free 2-in. InP layer bonded on a Si substrate was realized, and a low interfacial resistance and ohmic contact through the bonded interface were observed. After the MOVPE process, the as-grown structure was optically active and we observed photoluminescence (PL) intensity comparable to that from the same structure grown on InP as a reference. Furthermore, almost no lattice strain was observed from the InP layer. Then, the epitaxial growth of a GaInAsP–InP double-hetero (DH) laser diode (LD) was demonstrated on the substrate and we observed lasing emission at RT in a pulse regime. These results are promising for the integration of InP-based devices on a Si platform for optical interconnection.

Strain-driven synthesis of 〈112〉 direction InAs nanowires in V-grooved trenches on Si using InP/GaAs buffer layers

The catalyst-free metal organic vapor phase epitaxial growth of InAs nanowires on silicon (001) substrates is investigated by using selectively grown InP/GaAs buffer layers in V-grooved trenches. A strain-driven mechanism of self-aligned 〈112〉 direction InAs nanowires growing is proposed and demonstrated by the transmission electron microscopy measurement. The morphology of InAs nanowires is tapered in diameter and exhibits a hexagonal cross-section. The defect-free InAs nanowire shows a pure zinc blende crystal structure and an epitaxial relationship with InP buffer layer.

GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of {111} planes and an apex formed by {137} and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

Catalyst-free growth of InP nanowires on patterned Si (001) substrate by using GaAs buffer layer

The catalyst-free metal organic vapor phase epitaxial growth of InP nanowires on silicon (001) substrate is investigated using selectively grown GaAs buffer layers in V-shaped trenches. A yield up to 70% of nanowires is self-aligned in uncommon 〈112〉 directions under the optimized growth conditions. The evolution mechanism of self-aligned 〈112〉 directions for nanowires is discussed and demonstrated. Using this growth method, we can achieve branched and direction switched InP nanowires by varying the V/III ratio in situ. The structure of the nanowires is characterized by scanning electron microscope and transmission electron microscopy measurements. The crystal structure of the InP nanowires is stacking-faults-free wurtzite with its c axis perpendicular to the nanowire axis.

Three-dimensional reciprocal space mapping with a two-dimensional detector as a low-latency tool for investigating the influence of growth parameters on defects in semipolar GaN

A rapid nondestructive defect assessment and quantification method based on X-ray diffraction and three-dimensional reciprocal-space mapping has been established. A fast read-out two-dimensional detector with a high dynamic range of 20 bits, in combination with a powerful data analysis software package, is set up to provide fast feedback to crystal growers with the goal of supporting the development of reduced defect density GaN growth techniques. This would contribute strongly to the improvement of the crystal quality of epitaxial structures and therefore of optoelectronic properties. The method of normalized three-dimensional reciprocal-space mapping is found to be a reliable tool which shows clearly the influence of the parameters of the metal–organic vapour phase epitaxial and hydride vapour phase epitaxial (HVPE) growth methods on the extent of the diffuse scattering streak. This method enables determination of the basal stacking faults and an exploration of the presence of other types of defect such as partial dislocations and prismatic stacking faults. Three-dimensional reciprocal-space mapping is specifically used in the manuscript to determine basal stacking faults quantitatively and to discuss the presence of partial dislocations. This newly developed method has been applied to semipolar GaN structures grown on patterned sapphire substrates (PSSs). The fitting of the diffuse scattering intensity profiles along the stacking fault streaks with simulations based on a Monte Carlo approach has delivered an accurate determination of the basal plane stacking fault density. Three-dimensional reciprocal-space mapping is shown to be a method sensitive to the influence of crystallographic surface orientation on basal stacking fault densities during investigation of semipolar (11{\overline 2}2) GaN grown on an r-plane (1{\overline 1}02) PSS and semipolar (10{\overline 1}1) GaN grown on an n-plane (11{\overline 2}3) PSS. Moreover, the influence of HVPE overgrowth at reduced temperature on the quality of semipolar (11{\overline 2}2) GaN has been studied.

Towards a monolithically integrated III–V laser on silicon: optimization of multi-quantum well growth on InP on Si

High-quality InGaAsP/InP multi-quantum wells (MQWs) on the isolated areas of indium phosphide on silicon necessary for realizing a monolithically integrated silicon laser is achieved. Indium phosphide layer on silicon, the pre-requisite for the growth of quantum wells is achieved via nano-epitaxial lateral overgrowth (NELOG) technique from a defective seed indium phosphide layer on silicon. This technique makes use of epitaxial lateral overgrowth (ELOG) from closely spaced (1 µm) e-beam lithography-patterned nano-sized openings (∼300 nm) by low-pressure hydride vapor phase epitaxy. A silicon dioxide mask with carefully designed opening patterns and thickness with respect to the opening width is used to block the defects propagating from the indium phosphide seed layer by the so-called necking effect. Growth conditions are optimized to obtain smooth surface morphology even after coalescence of laterally grown indium phosphide from adjacent openings. Surface morphology and optical properties of the NELOG indium phosphide layer are studied using atomic force microscopy, cathodoluminescence and room temperature µ-photoluminescence (µ-PL) measurements. Metal organic vapor phase epitaxial growth of InGaAsP/InP MQWs on the NELOG indium phosphide is conducted. The mask patterns to avoid loading effect that can cause excessive well/barrier thickness and composition change with respect to the targeted values is optimized. Cross-sectional transmission electron microscope studies show that the coalesced NELOG InP on Si is defect-free. PL measurement results indicate the good material quality of the grown MQWs. Microdisk (MD) cavities are fabricated from the MQWs on ELOG layer. PL spectra reveal the existence of resonant modes arising out of these MD cavities. A mode solver using finite difference method indicates the pertinent steps that should be adopted to realize lasing.

Metal–Organic Vapor Phase Epitaxy Growth of Embedded Gallium Nitride Nanocolumn for Reduction in Dislocation Density

The use of nanocolumn crystals is thought to be effective in producing a low-dislocation-density GaN layers. In this paper, we propose a metal–organic vapor phase epitaxial (MOVPE) growth method for producing uniform GaN nanocolumns using deep through-holes in a thick SiO2 selective growth mask. A SiO2 film with a thickness of 500 nm was deposited by sputtering on an AlN buffer layer/SiC substrate. A nanoimprinting technique was applied to produce dot openings. Then, dry etching with CF4 gas was carried out to form deep through-holes in the SiO2 film. In the second MOVPE growth, individual GaN nanocolumns coalesced into a planarized GaN layer, after thinning the SiO2 mask to 100 nm. A cathode-luminescence image of the GaN layer on a GaN nanocolumn template shows a low dislocation density of 1.3×108 cm-2, while that of a GaN layer directly grown on an AlN buffer layer shows a dislocation density of 9.4×108 cm-2.

MOVPE GROWTH OF THE InP BASED MID-IR EMISSION QUANTUM DOT STRUCTURES

In this paper, semiconductor quantum dot structures for mid-infrared emission were self-assembled on InP substrate by using metal–organic vapor phase epitaxy growth. The InAs quantum dots grown at different conditions have been investigated. To improve the grown quantum dot's shape, the dot density and the dot size uniformity, a two-step growth method has been used and investigated. By changing the composition of the In x Ga 1-x As matrix layer of the InAs / In x Ga 1-x As / InP quantum dot structure, emission wavelength of the InAs quantum dot structure has been extended to the longest > 2.35 μm measured at 77 K. For the narrower bandgap semiconductor InAsSb quantum dots, the emission wavelength was measured at > 2.8 μm.

Investigation of Growth Mechanism for InGaN by Metal–Organic Vapor Phase Epitaxy Using Computational Fluid Simulation

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

MOVPE Growth of InxGa1−xN (x ∼ 0.4) and Fabrication of Homo-junction Solar Cells

The metal organic vapor phase epitaxy (MOVPE) growth of indium gallium nitride (InGaN) has been discussed in detail towards the fabrication of solar cell. The InGaN film with In contents up to 0.4 are successfully grown by controlling the fundamental growth parameters such as the precursor gas flow rates, temperature etc . The formation of metallic In originates from the higher value (0.74) of trimethylindium/(trimethylindium + triethylgallium) (TMI/(TMI + TEG)) molar ratio with low (4100) V/III weight molar ratio while the lower value (0.2) of TMI/(TMI + TEG) causes the phase separation. It is also necessary to control the growth rate and epitaxial film thickness to suppress the phase separation in the material. The crystalline quality of grown films is studied and it is found to be markedly deteriorated with increasing In content. The lattice parameters as well as the thermal expansion coefficient mismatch between GaN template and InGaN epi-layer are primarily considered as the reasons to deteriorate the film quality for higher In content. By using In 0.16 Ga 0.84 N films, an n + –p homo-junction structure is fabricated on 0.65 μm GaN template. For such a device, the response to the light illumination (AM 1.5) is observed with an open circuit voltage of 1.4 V and the short circuit current density of 0.25 mA/cm 2 . To improve the performance as well as increase solar photon capturing, the device is further fabricated on thick GaN template with higher In content. The In 0.25 Ga 0.75 N n + –p junction solar cell is found better performance with an open circuit voltage of 1.5 V and the short circuit current density of 0.5 mA/cm 2 . This is the InGaN p–n homo-junction solar cell with the highest In content ever reported by MOVPE.

Fabrication of ridge‐shaped AlGaInP/GaInP quantum well structure for observation of evanescent wave coupling effect

AbstractA ridge‐shaped AlGaInP/GaInP quantum well (QW) structure with a ridge top width in the sub‐wavelength region (500–600 nm) is successfully fabricated by selective area metal organic vapor phase epitaxial growth on patterned GaAs substrates, as the first step towards the realization of high‐efficiency light‐emitting diodes (LEDs) utilizing the evanescent wave coupling effect. It is confirmed by an X‐ray diffraction study that AlGaInP layers grown on all the different facets of the ridge structure satisfy the lattice matching requirements for high‐efficiency LED applications. A considerable enhancement of the light‐extraction efficiency in the fabricated ridge‐shaped QW structure is demonstrated by means of a photoluminescence analysis. The realization of the evanescent wave coupling effect is suggested by theoretical simulation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of the Axial Heterojunction in GaSb/InAs(Sb) Nanowires with High Crystal Quality

Switching of the group-III element in III–V nanowire heterostructures is difficult due to the high solubility of group-III atoms in the Au seed particle. In addition, switching from Sb to a different group-V element has not been achieved in binary materials, largely due to its high solubility in Au. In metal–organic vapor phase epitaxy (MOVPE) growth, the use of Sb precursors presents further complications due to reactor background contamination. In this paper, we demonstrate growth of GaSb/InAs(Sb) nanowire heterostructures with potential applications in tunneling devices and study the processes occurring during the transition from GaSb to InAs growth. We show how the heterostructure can be grown with a sharp transition by taking advantage of a growth stop, which occurs naturally as the Au seed particle is emptied of Ga and filled with In. The remaining Sb background in the reactor during the InAs growth results in a finite Sb incorporation into this segment. This has the advantage of suppressing stackin...