Selective Metalorganic Vapor Phase Research Articles

Self-assembled InN quantum dots on side facets of GaN nanowires

Self-assembled, atomic diffusion controlled growth of InN quantum dots was realized on the side facets of dislocation-free and c-oriented GaN nanowires having a hexagonal cross-section. The nanowires were synthesized by selective area metal organic vapor phase epitaxy. A 3 Å thick InN wetting layer was observed after growth, on top of which the InN quantum dots formed, indicating self-assembly in the Stranski-Krastanow growth mode. We found that the InN quantum dots can be tuned to nucleate either preferentially at the edges between GaN nanowire side facets, or directly on the side facets by tuning the adatom migration by controlling the precursor supersaturation and growth temperature. Structural characterization by transmission electron microscopy and reciprocal space mapping show that the InN quantum dots are close to be fully relaxed (residual strain below 1%) and that the c-planes of the InN quantum dots are tilted with respect to the GaN core. The strain relaxes mainly by the formation of misfit dislocations, observed with a periodicity of 3.2 nm at the InN and GaN hetero-interface. The misfit dislocations introduce I1 type stacking faults (…ABABCBC…) in the InN quantum dots. Photoluminescence investigations of the InN quantum dots show that the emissions shift to higher energy with reduced quantum dot size, which we attribute to increased quantum confinement.

Influence of adatom migration on wrinkling morphologies of AlGaN/GaN micro-pyramids grown by selective MOVPE**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 61574173), the National Key Research and Development Program, China (Grant No. 2016YFB0400105), the International Science and Technology Collaboration Program of Guangdong Province, China (Grant No. 2013B051000041), the International Science and Technology Collaboration Program

GaN micro-pyramids with AlGaN capping layer are grown by selective metal–organic–vapor phase epitaxy (MOVPE). Compared with bare GaN micro-pyramids, AlGaN/GaN micro-pyramids show wrinkling morphologies at the bottom of the structure. The formation of those special morphologies is associated with the spontaneously formed AlGaN polycrystalline particles on the dielectric mask, owing to the much higher bond energy of Al–N than that of Ga–N. When the sizes of the polycrystalline particles are larger than 50 nm, the uniform source supply behavior is disturbed, thereby leading to unsymmetrical surface morphology. Analysis reveals that the scale of surface wrinkling is related to the migration length of Ga adatoms along the AlGaN facet. The migration properties of Al and Ga further affect the distribution of Al composition along the sidewalls, characterized by the μ-PL measurement.

GaN Rods Grown on Si by SAG-HVPE toward GaN HVPE/InGaN MOVPE Core/Shell Structures

Selective area growth hydride vapor phase epitaxy (SAG-HVPE) and metal organic vapor phase epitaxy (MOVPE) processes are coupled for the synthesis of high quality c-axis InGaN/GaN core/shell structures. The core consists of high aspect ratio GaN rods grown by SAG-HVPE on patterned N-polar AlN on Si(100) substrates. The shell is grown by MOVPE which provides abrupt InGaN/GaN multiquantum wells (MQWs). Microphotoluminescence (μ-PL) analysis performed on the HVPE GaN core exhibit a narrow emission line of 3 meV in line width associated with the neutral-donor bound exciton revealing the excellent optical properties of the GaN material. For the core/shell wire geometry, the silane free HVPE process ensured the whole lateral cladding of the core. The hybrid HVPE core/MOVPE shell structures exhibit high optical quality without yellow luminescence.

Migration characterization of Ga and In adatoms on dielectric surface in selective MOVPE**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 51177175), the National Basic Research Program of China (Grant No. 2011CB301903), the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 20110171110021), the International Sci. & Tech. Collaboration Program of China (Grant

Migration characterizations of Ga and In adatoms on the dielectric surface in selective metal organic vapor phase epitaxy (MOVPE) were investigated. In the typical MOVPE environment, the selectivity of growth is preserved for GaN, and the growth rate of GaN micro-pyramids is sensitive to the period of the patterned SiO2 mask. A surface migration induced model was adopted to figure out the effective migration length of Ga adatoms on the dielectric surface. Different from the growth of GaN, the selective area growth of InGaN on the patterned template would induce the deposition of InGaN polycrystalline particles on the patterned SiO2 mask with a long period. It was demonstrated with a scanning electron microscope and energy dispersive spectroscopy that the In adatoms exhibit a shorter migration length on the dielectric surface.

The influence of aluminum content on the surface morphology of heavily doped (Al)GaN mesastrip structures grown by selective metalorganic vapor phase epitaxy

Heavily Si-doped Al x Ga1–x N mesastrip structures were grown by selective MOVPE technology. Al x Ga1–x N:Si mesastructures with x ~ 0.01–0.07 possess a smoother top and more even side surfaces as compared to those in analogous GaN:Si structures. During the growth of mesastructures with x ~ 0.03–0.07, a thin nanocrystalline AlN deposit appears on the Si3N4 mask. This deposit is not formed during the growth of structures with sufficiently low aluminum content.

Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

Proposal and Analysis of Distributed Reflector-Laser Diode Integrated with an Electroabsorption Modulator

A novel integrated laser, that is, a distributed reflector laser diode integrated with an electroabsorption modulator, is proposed to improve the output efficiency, single-mode stability, and chirp. The proposed laser can be realized using the selective metalorganic vapor phase epitaxy technique (that is, control of the width of the insulating mask), and its fabrication process is almost the same as the conventional electroabsorption modulated laser (EML) process except for the asymmetric coupling coefficient structure along the cavity. For our analysis, an accurate time-domain transfer-matrix-based laser model is developed. Based on this model, we perform steady-state and large-signal analyses. The performances of the proposed laser, such as the output power, extinction ratio, and chirp, are compared with those of the EML. Under 10-Gbps NRZ modulation, we can obtain a 30% higher output power and about 50% lower chirp than the conventional EML. In particular, the simulation results show that the chirp provided by the proposed laser can appear to have a longer wavelength side at the leading edge of the pulse and a shorter wavelength side at the falling edge.

Ga(In)N Photonic Crystal Light Emitters with Semipolar Quantum Wells

We present directional photonic crystal light emitters produced as periodic semipolar GaInN quantum wells, grown by selective area metal organic vapour phase epitaxy. The emitted angle-dependent modal structure for sub-micrometer stripes and embedded photonic crystal structures is analyzed experimentally in detail, and the introduction of an Al0.12Ga0.88N cladding layer is investigated. We provide a complete simulation based on the finite-difference time-domain method, which allows to identify all leaky modes as well as their spectral and angular dependence.

From conformal overgrowth to lateral growth of indium arsenide nano structures on silicon substrates by MOVPE

A methodology for the deposition of lateral InAs nanostructures on silicon by selective area metal organic vapor phase epitaxy (SA-MOVPE) is presented. Growth parameters which are optimal for the SA-MOVPE of conformal InAs overgrowth on GaAs nanowires were transferred to the lateral SA growth of InAs structures on patterned silicon substrates. The substrate pretreatment conditions and growth parameters were further optimized with respect to selectivity and nanostructure morphology. It is found that lateral growth of InAs nano structures can be achieved on patterned Si(110) as well as on patterned silicon on insulator (SOI) substrates. An investigation of the laterally grown InAs/Si nanowires' crystal structure revealed a faceted but nevertheless abrupt Si–InAs interface on the Si(110) substrate as well as relaxation and a high crystallinity of the deposited InAs on both Si template types. The morphology and crystallinity of laterally grown structures are discussed in detail and compared to that of vertical shell/core InAs/GaAs nanowires.

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)

Comparison of InAs nanowire conductivity: influence of growth method and structure

AbstractThe conductivity and crystal structure of nominally undoped InAs nanowires deposited by three different methods – 1. selective area metal organic vapor phase epitaxy (SA MOVPE), 2. gold assisted vapor liquid solid (VLS) MOVPE and 3. extrinsic catalyst free VLS molecular beam epitaxy (MBE) – is investigated. The influence on conductivity by stacking faults and different growth conditions is analyzed to determine the main impact. It is found that in terms of crystal structure, nanowires deposited by VLS MOVPE and VLS MBE behave similarly showing a zinc blende (ZB) phase while nanowires deposited by SA MOVPE feature a high density of stacking faults and a tendency to higher amounts of wurtzite (WZ) when grown with a decreased growth rate. However, the conductivity of wires deposited by VLS MOVPE is found to be much higher and statistically less dispersive compared to the other two wire types. An electrical similarity between nominally undoped wires in VLS MOVPE and previously reported intentionally doped wires in SA MOVPE is observed and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Drastic Reduction of Dislocation Density in Semipolar (1122) GaN Stripe Crystal on Si Substrate by Dual Selective Metal–Organic Vapor Phase Epitaxy

A drastic reduction of the dislocation density in a semipolar (1122) GaN stripe on a patterned Si substrate was achieved by the two-step selective growth of a GaN stripe. After depositing a SiO2 mask on the (1122) and (0001) faces of a GaN stripe grown on a (113) Si substrate, GaN was regrown only on the (1122) face. The dislocation density estimated from the dark-spot density in a cathodoluminescence (CL) image greatly decreased from 4.0×108 to 1.0×105/cm2 in the regrowth region. A transmission electron microscopy (TEM) image also verified that there were no dislocations at the regrowth interfaces.

Drastic Reduction of Dislocation Density in Semipolar (1122) GaN Stripe Crystal on Si Substrate by Dual Selective Metal–Organic Vapor Phase Epitaxy

A drastic reduction of the dislocation density in a semipolar (1122) GaN stripe on a patterned Si substrate was achieved by the two-step selective growth of a GaN stripe. After depositing a SiO2 mask on the (1122) and (0001) faces of a GaN stripe grown on a (113) Si substrate, GaN was regrown only on the (1122) face. The dislocation density estimated from the dark-spot density in a cathodoluminescence (CL) image greatly decreased from 4.0×108 to 1.0×105/cm2 in the regrowth region. A transmission electron microscopy (TEM) image also verified that there were no dislocations at the regrowth interfaces.

Impact of base size and shape on formation control of multifaceted InP nanopyramids by selective area metal organic vapor phase epitaxy

We report the impact of base size and shape on the evolution control of multifaceted InP (100) nanopyramids grown by selective area metal organic vapor phase epitaxy. The pyramid top surfaces are composed of a (100) center facet surrounded by high-index {103} and {115} facets. Their arrangement and (relative) size depend on the size and shape of the pyramid top area. For a certain shape, only the (100) facet remains below a critical size of the top area. The arrangement and (relative) size of the top facets in turn are governed by the {110} and {111} side facets whose area (ratio) depends on the pyramid base size and shape. This self-consistently determines the ratio of the (100) top facet area and the sum of the {110} and {111} side facet areas as well as the height of the pyramids.

MOVPE of n-doped GaAs and modulation doped GaAs/AlGaAs nanowires

Two different fabrication approaches were compared to obtain conductive GaAs nanowires: on one hand by modulation doping of GaAs/AlGaAs core/shell nanowires, on the other hand by Si-doping of GaAs nanowires. Modulation doped GaAs/AlGaAs core–shell nanowires were grown by selective area metal organic vapor phase epitaxy (MOVPE) on GaAs (1 1 1) substrates. The influences of growth parameters and mask design on aspect ratio of the core structures were investigated. The specialty of this study was that the growth mode was switched from vertical GaAs wire growth to the AlGaAs conformal shell overgrowth by intentionally changing the growth chemistry from the use of a more stable group III source – trimethylgallium (TMGa) to more easily decomposed sources – the alternative sources triethylgallium (TEGa) and dimethylethylaminealane (DMEAAl). It was found that the diameter and length of the core structures strongly depend on the arsenic partial pressure and growth temperature as well as mask design. The uniformity of shell growth is also influenced by the mask design. Additionally an alternative approach for the production of conductive GaAs nanowires was under study. To this end, the influence of Si-doping on GaAs core growth was investigated. It was found that doping has a detrimental impact on growth morphology leading to an undesirable enhanced growth rate on the nanowire side facets.

1.55 μm InAs quantum dot distribution on truncated InP pyramids and regrowth by selective area epitaxy

Position and distribution control of 1.55-μm InAs quantum dots (QDs) on truncated InP pyramids grown by selective area Metal Organic Vapor Phase Epitaxy (MOVPE) is reported. The arrangement of the {103}, {115}, and (100) facets on the pyramid top surface is governed by the shape of the pyramid base and top surface area. This allows the precise position and distribution control of the QDs due to preferential nucleation on the {103} and {115} facets. With shrinking QD number upon reduced top surface area, sharp emission from single QDs is observed at 1.55 μm. Regrowth of a passive InP structure around the pyramids establishes submicrometer-scale active-passive integration for efficient microcavity QD nanolasers and single photon sources operating in the 1.55-μm telecom wavelength region and their implementation in photonic integrated circuits.

Distribution control of 1.55μm InAs quantum dots down to small numbers on truncated InP pyramids grown by selective area metal organic vapor phase epitaxy

Distribution control of InAs quantum dots (QDs) on truncated InP pyramids by selective area growth is reported. The top surface of the pyramids is composed of a (100) facet and high-index facets aside. The arrangement of the facets is governed by the shape of the pyramid base and top surface area. The QDs preferentially nucleate on the high-index facets determining position and distribution. The QD number is reduced with shrinking top surface size. Positioning of four, three, two, and single QDs is realized depending on the top surface’s shape and size. Emission from single QDs is observed at 1.55μm.

MOVPE growth and properties of GaN on (1 1 1)Si using an AlInN intermediate layer

Using an AlInN intermediate layer, GaN was grown on (1 1 1)Si substrate by selective metalorganic vapor phase epitaxy. The variation of the surface morphology was investigated as a function of the In composition and thickness of the AlInN layer. It was found that the In composition in the AlInN layer was a function of the growth temperature and thickness. Because of the small band offset at the AlInN/Si hetero-interface, we have achieved a low series resistance of the order of 9 Ω (0.0036 Ω cm 2) across the GaN/AlInN/AlN/Si layer structure.

Longitudinal bandgap modulated broadband (>150 nm) InGaAs/GaAs MQWs superluminescent diodes by selective area MOVPE growth

The characteristics of broadband superluminescent diodes (SLDs) are presented. The longitudinal bandgap modulated InGaAs/GaAs multiple quantum wells of broadband SLDs are grown by selective area metal organic vapour phase epitaxy (MOVPE) growth. The centre wavelength was 1060 nm. The 3 dB bandwidth was 130 nm and the 10 dB bandwidth was 174 nm. The output power was 0.3 mW.

Nonlinear Kinetic Analysis of InP and InAs Metal Organic Vapor Phase Epitaxy by Selective Area Growth Technique

Kinetic analysis based on the combination of selective area metal organic vapor phase epitaxy (SA-MOVPE) and two-dimensional numerical simulation can be used to extract real surface kinetics, which usually remain unknown because the growth rate of deposited film is limited by diffusional mass-transfer rate in SA-MOVPE. To explain previously observed concentration dependency on surface reaction rate constant and to establish a more reliable model for the surface process, non-linear surface kinetics were used in this study to analyze SA-MOVPE process for InP and InAs. Surface reaction rate constant (ksn) and adsorption equilibrium constant (K) of a film precursor in a nonlinear model was successfully extracted in SA-MOVPE for InP and InAs. Results show that a nonlinear model that takes adsorption–desorption equilibrium into account can well explain the concentration dependency and can be potentially used in predicting growth behavior regardless of mask width or partial pressure influence.