Area Metalorganic Vapor Phase Epitaxy Research Articles

Structural and optical characteristics of ∼ 1.65 μm-emitting quantum dots on InP substrate grown by selected area-MOVPE

Diblock co-polymer lithography and selected area metalorganic vapor phase epitaxy was used to fabricate quantum dots (QDs) on InP substrates for application in C- band communication. Initial structural and optical studies were carried out on three layered quantum dots with compressively strained In0.76Ga0.24As well and lattice-matched either In0.53Ga0.47As or In0.52Al0.48As as barriers. Photoluminescence studies at room temperature and at low temperature indicated weak carrier confinement in the QDs with In0.53Ga0.47As barrier, which leads to its broader PL linewidth, compared to QDs with In0.52Al0.48As barrier. This makes InAlAs a better choice for the barrier material in device applications. However, the higher growth rate of InAlAs inside the selected area and shape of the dots resulting from in-situ etching are some issues that need to be addressed to optimize the optical properties of QDs.

Characterization of the parasitic masking layer formed during GaN SA-MOVPE using PECVD SiO2 masks

X-ray photoelectron spectroscopy (XPS) was used to study the surface composition of the parasitic masking layer formed during selective area metalorganic vapor phase epitaxy (MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD). It was shown that non-stoichiometric silicon oxynitride layer (SiOxNy) is responsible for the inhibition of GaN nucleation in the vicinity of the SiO2 mask. Atomic force microscopy (AFM) was applied to examine the surface topography, whereas scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) techniques were used for the purpose of electrical characterization of the parasitic masking layer. The overgrowth of GaN islands through the discontinuities in the SiOxNy film was shown. The SCM imaging showed the presence of a positive electric charge in the parasitic masking layer, indicating the accumulation of defects in the silicon oxynitride film.

Parasitic masking effect in GaN SA-MOVPE using SiO2 masks deposited by the PECVD technique

The paper reports a phenomenon of parasitic substrate masking during selective area metalorganic vapor phase epitaxy (SA-MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD) at pressures above 150 hPa. The discussion of the thermal stability and nitridation process of the SiO2 films is followed by the presentation of the experimental work results focused on the investigation of the relationship between the parasitic masking effect and pressure in the MOVPE reactor chamber. Analysis of the surface morphology is conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM). A hypothesis was proposed explaining the formation of the deposition-free region that indicates silanimine (HNSi) layer formation as a possible factor responsible for the adverse inhibition of GaN nucleation.

Deformed Honeycomb Lattices of InGaAs Nanowires Grown on Silicon‐on‐Insulator for Photonic Crystal Surface‐Emitting Lasers

AbstractPhotonic crystals can be used to achieve high‐performance surface‐emitting lasers and enable novel photonic topological insulator devices. In this work, a GaAs/InGaAs heterojunction nanowire platform by selective area metalorganic vapor phase epitaxy for such applications is demonstrated. The nanowires are arranged into deformed honeycomb lattices on silicon‐on‐insulator substrate to exploit the quadrupolar photonic band‐edge mode. Core–shell and axial heterostructures are formed with their crystalline properties studied by scanning transmission electron microscopy. Room‐temperature, single mode lasing from both stretched and compressed honeycomb lattices within the telecom‐O band, with lasing threshold as low as 1.25 µJ cm−2 is demonstrated. The potential of using InGaAs nanowire‐based honeycomb lattices for small‐divergence surface‐emitting lasers and topological edge mode lasers is investigated. Finite‐difference time‐domain far field simulations suggest a sub‐10° beam divergence can be achieved thanks to the out‐of‐plane diffraction.

Emission color modulation of InGaN/GaN multiple quantum wells by selective area metalorganic vapor phase epitaxy on hexagonal windows

We investigated influences of mask pattern on the emission from InGaN multiple quantum wells through the differences in plane orientation appearing on the multifaceted islands in selective area metalorganic vapor phase epitaxy. Cathodoluminescence mapping confirmed that emission colors changed depending on the crystal plane. Photoluminescence spectroscopy showed that the emission wavelength red-shifted by increasing the mask width. By combining the difference of indium incorporation efficiency depending on the crystal plane and the lateral vapor phase diffusion effect, multiple quantum wells with different emission wavelengths of up to 106 nm were grown simultaneously in the microscale region.

A New Strategy for Selective Area Growth of Highly Uniform InGaAs/InP Multiple Quantum Well Nanowire Arrays for Optoelectronic Device Applications

AbstractIII‐V semiconductor nanowires with quantum wells (QWs) are promising for ultra‐compact light sources and photodetectors from visible to infrared spectral region. However, most of the reported InGaAs/InP QW nanowires are based on the wurtzite phase and exhibit non‐uniform morphology due to the complex heterostructure growth, making it challenging to incorporate multiple‐QWs (MQW) for optoelectronic applications. Here, a new strategy for the growth of InGaAs/InP MQW nanowire arrays by selective area metalorganic vapor phase epitaxy is reported. It is revealed that {110} faceted InP nanowires with mixed zincblende and wurtzite phases can be achieved, forming a critical base for the subsequent growth of highly‐uniform, taper‐free, hexagonal‐shaped MQW nanowire arrays with excellent optical properties. Room‐temperature lasing at the wavelength of ≈1 µm under optical pumping is achieved with a low threshold. By incorporating dopants to form an n+‐i‐n+ structure, InGaAs/InP 40‐QW nanowire array photodetectors are demonstrated with the broadband response (400–1600 nm) and high responsivities of 2175 A W−1 at 980 nm outperforming those of conventional planar InGaAs photodetectors. The results show that the new growth strategy is highly feasible to achieve high‐quality InGaAs/InP MQW nanowires for the development of future optoelectronic devices and integrated photonic systems.

Impact of InGaAs carrier collection quantum well on the performance of InAs QD active region lasers fabricated by diblock copolymer lithography and selective area epitaxy

Quantum dot (QD) laser diodes, where the active region consists of wetting-layer-free InAs QDs, were demonstrated by block copolymer (BCP) lithography and subsequent selective area metal-organic vapor phase epitaxy, which results in the QD density of ∼4 × 1010 cm2. In this work, we show that an In0.1Ga0.9As QW located in close proximity to the wetting-layer-free InAs QDs leads to an enhanced carrier injection into the QDs, allowing for lasing at room temperature (RT). Devices employing InAs QDs grown with and without In0.1Ga0.9As QW carrier collection layer exhibit lasing at 80 K, while only the lasers grown with the In0.1Ga0.9As QW exhibits lasing at RT. Driving current-dependent electroluminescence measurements reveals a low carrier injection into the QDs in the device grown without In0.1Ga0.9As QW carrier collection layer. In addition, the appearance of lasing emission, corresponding to high energy transitions, indicates a relatively flat gain profile for this InAs QD active region grown by SA-MOVPE. In addition, EL measurements at 80 K on devices employing varying thickness (dInAs) QDs indicate the peak emission wavelength varies from 920 nm (dInAs ∼ 1.5 nm) to 974 nm (dInAs = 3 nm), although the devices employing dInAs ∼ 3 nm did not exhibit lasing, possibly because of a significant degree of strain relaxation for this QD thickness.

3D GaN Fins as a Versatile Platform for a‐Plane‐Based Devices

GaN fins on GaN‐on‐sapphire templates are fabricated by continuous mode selective area metalorganic vapor phase epitaxy. The fins exhibit high aspect ratios and smooth nonpolar a‐plane sidewalls with an ultra‐low threading dislocation density of a few 105 cm−2 making them ideally suited for optoelectronic to electronic applications. A detailed analysis of the inner structure of GaN fins is provided by the help of marker layer experiments and correlation of results from fins fabricated under different growth conditions, leading to the development of a growth model to explain the final geometry and optical as well as electrical properties of these high aspect ratio fins. Distinctly different material properties for the central and outer parts of the fins are detected. Whereas the outer sidewalls represent high quality GaN surfaces with very low defect densities, a strong quenching of near band edge emission (NBE) in the central part of the fins is accompanied by heavy compensation of free electrons. A possible explanation is the incorporation of excessive point defects, like intrinsic defects or carbon impurity. The sidewall regions, however, prove to be highly suitable for device applications due to their strong NBE emission, low dislocation density, and high free carrier concentration.

Efficient Green Emission from Wurtzite Al xIn1- xP Nanowires.

Direct band gap III–V semiconductors, emitting efficiently in the amber–green region of the visible spectrum, are still missing, causing loss in efficiency in light emitting diodes operating in this region, a phenomenon known as the “green gap”. Novel geometries and crystal symmetries however show strong promise in overcoming this limit. Here we develop a novel material system, consisting of wurtzite AlxIn1–xP nanowires, which is predicted to have a direct band gap in the green region. The nanowires are grown with selective area metalorganic vapor phase epitaxy and show wurtzite crystal purity from transmission electron microscopy. We show strong light emission at room temperature between the near-infrared 875 nm (1.42 eV) and the “pure green” 555 nm (2.23 eV). We investigate the band structure of wurtzite AlxIn1–xP using time-resolved and temperature-dependent photoluminescence measurements and compare the experimental results with density functional theory simulations, obtaining excellent agreement. Our work paves the way for high-efficiency green light emitting diodes based on wurtzite III-phosphide nanowires.

High In-content InGaN nano-pyramids: Tuning crystal homogeneity by optimized nucleation of GaN seeds

Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 101¯1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 101¯1 and (0001). Typically, the InGaN growth on 101¯1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by 101¯1-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.

(Invited) III-V Selective Area Growth and Epitaxial Functional Oxides on Si: From Electronic to Photonic Devices

Driven by fabrication cost reduction and device performance improvement, the Silicon semiconductor industry continues its never-ending pursuit of new approaches for fabricating integrated circuits. In this context, the monolithic integration of III-V semiconductors epitaxially grown on Si substrate have been attracting much attention as building blocks for next-generation electronics and photonics due to their potential intrinsic properties. Direct heteroepitaxy of III-V compound semiconductors on Si has traditionally represented a formidable challenge, due to the high material mismatch (lattice parameter, polarity, thermal coefficient, ...) between Si and III-V semiconductors generating high density of defect density during the epitaxial process. To overcome this, selective area growth of III-Vs in a pre-patterned Si substrate by Selective Area Metal-Organic Vapor Phase Epitaxy allow the possibility to obtain high quality and reduced defect density III-V based active layers onto standard Si(001) substrate. Using this approach we integrate III-V materials monolithically on Si while focusing on both ultimate trench widths (W < 20 nm) scaling as well as relaxed trench dimension in function of the targeted application. We report here on the heteroepitaxy of InP buffer on initiated from a <111> V-groove Si surface and discuss the unique relaxation mechanism of such compound with respect to Si substrate. We derived a fundamental understanding and theoretical modeling of the growth mechanisms in STI trenches as well as the determining role of the InP nucleation layer. The subsequent growth approach of InGaAs active layer, used for both nFET or Laser applications, is further studied. Finally, III-V based electronic and photonic devices realized using selective area growth technique are presented and benchmarked to the current state of the art.

(Invited) Monolithic Integration of III-V Semiconductors by Selective Area Growth on Si(001) Substrate: Epitaxy Challenges & Applications

Driven by fabrication cost reduction and device performance improvement, the Silicon semiconductor industry continues its never-ending pursuit of new approaches for fabricating integrated circuits. Monolithic integration of III-V semiconductors epitaxially grown on Si substrate have been attracting much attention as building blocks for next-generation electronics and photonics due to their potential intrinsic properties. Direct heteroepitaxy of III-V compound semiconductors on Si has traditionally represented a formidable challenge, due to the extensive lattice mismatch of 8% between the Si substrate and high mobility III-V compounds, such as In0.53Ga0.47As/InP heterostructure. The defect confinement technique has recently attracted great interest due to the possibility of obtaining high quality III-V based active layers on Si. Using this approach we integrate III-V materials monolithically on Si through the epitaxial growth of III-V materials into a pre-patterned structure by Selective Area Metal-Organic Vapor Phase Epitaxy. We report here on the growth of InP on STI patterned Si wafers using the defect confinement technique while focusing on scaled trench widths (W < 50 nm). We demonstrate the impact of the crystalline alignment of the InP layer with the underlying substrate by exploring as starting geometry at the bottom in between the STI either a rounded etch pit covered with a Ge buffer layer versus a crystalline <111> V-groove structure in Si. We show the large impact of the main layer growth temperature and the growth pressure on the trench filling, the growth uniformity and the crystal quality which we could correlate with changes in resistivity and the presence of impurity diffusion in the III-V layer. Moreover, we derived a fundamental understanding and theoretical modeling of the growth mechanisms in STI trenches and the determining role of the nucleation layer. This lead to a strong enhancement of the crystalline quality and growth uniformity of the InP semiconductor. As a conclusion, this study of III-V selective area growth brings some elements for the optimization of the heteroepitaxy of III-V compounds on (001) oriented Si substrates. The demonstration of a clear reduction in defect density along the trench orientation is original and obviously confirm the potential of this heterogeneous integration option for high mobility logic devices, and photonic applications on a common Si platform.

(Invited) Selective-Area Metal Organic Vapor-Phase Epitaxy of InGaAs/InP Heterostrucures on Si for Advanced CMOS Devices

Driven by fabrication cost reduction and device performance improvement, the Silicon semiconductor industry continues its never-ending pursuit of new approaches for fabricating integrated circuits. The heterogeneous integration of III-V high mobility semiconductors on a silicon platform in a 3D architecture such as Fin-Field-Effect-Transistor (FinFET) is a winning combination to further boost the performance of future CMOS devices.Direct heteroepitaxy of III-V compound semiconductors on Si has traditionally represented a formidable challenge, due to the extensive lattice mismatch of 8% between the Si substrate and high mobility III-V compounds, such as In0.53Ga0.47As/InP heterostructure. The defect confinement technique has recently attracted great interest due to the possibility of obtaining high quality III-V based active regions, using nanometer scale trenches with high aspect ratio (>3) in order to eliminate (111)-oriented defects (such as threading dislocations, twins or stacking faults) on the sidewalls. Using this approach we integrate III-V materials monolithically on Si through the epitaxial growth of III-V materials into a pre-patterned structure by Selective Area Metal-Organic Vapor Phase Epitaxy (SA-MOVPE). Silicon 300mm wafers substrates patterned with ~300nm deep Shallow Trench Isolation (STI) structures are used with trenches having typical widths ranging from 500 nm down to ~20nm.We report here on the SA-MOVPE growth of InP on STI patterned Si wafers using the defect confinement technique while focusing on scaled trench widths (W < 50 nm). We demonstrate the impact of the crystalline alignment of the InP layer with the underlying substrate by exploring as starting geometry at the bottom in between the STI either a rounded etch pit covered with a Ge buffer layer versus a crystalline <111> V-groove structure in Si. The structures are fully characterized by Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, X-Ray Diffraction, Secondary Ion Mass Spectroscopy and Scanning Spreading Resistance Microscopy. We demonstrate the dependence of the material quality and trench filling upon different sets of growth conditions.We show the large impact of the main layer growth temperature and the growth pressure on the trench filling, the growth uniformity and the crystal quality which we could correlate with changes in resistivity and the presence of impurity diffusion in the III-V layer. Moreover, we derived a fundamental understanding and theoretical modeling of the growth mechanisms in STI trenches and the determining role of the nucleation layer. This lead to a strong enhancement of the crystalline quality and growth uniformity of the InP semiconductor.As a conclusion, this study of the InP selective area growth brings some elements for the optimization of the heteroepitaxy of III-V compounds on patterned Si substrates. The demonstration of a clear reduction in defect density along the trench orientation is an original achievement and confirms the potential of heterogeneous integration approach for advanced III-V based logic devices or III-V based photonic applications on a common Si platform.

Growth rate and composition of InGaN during InGaN/GaN quantum wells selective area metal-organic vapor phase epitaxy considering surface diffusion

Film growth rate and composition variation were numerically analyzed during the selective area growth of InGaN on both GaN triangular stripe and hexagonal pyramid microfacets. To obtain the In composition of the film, concentration of In and Ga atoms due to the surface diffusion was added to the concentration determined from the Laplace equation that governs the gas phase diffusion. When the surface diffusion is considered, the In composition and resulting wavelength increased compared to the results obtained from the vapor phase diffusion model. The In content also increased according to the increasing mask width.

INGAN/GAN based semipolar green converters

In order to achieve highly efficient green light emission, we are investigating the realization of InGaN-based luminescence conversion structures optically pumped by a blue LED. Using selective area metalorganic vapor phase epitaxy, we have grown inverted pyramid structures. On the side facets of these structures, semipolar InGaN/GaN multi-quantum wells can be deposited which may have promising characteristics for high luminescence conversion efficiencies. In order to enhance the green emission intensity, both the absorption of the blue excitation light and the conversion to green light must be optimized. By varying the growth parameters, we could stabilize the formation of {101¯1} semipolar facets resulting in better quantum well morphology and hence better green light conversion. Moreover, the QW number is optimized to make a balance between thermal load – decreasing the quality of the early grown quantum wells – and the lower quality of the quantum wells grown on top of many others. The thermal load has been identified as a very critical parameter for such structures emitting green light at about 505nm.

Morphology evolution and optical properties of GaN nano‐pyramids grown by selective area MOVPE

AbstractThe evolution of GaN nano‐pyramid growth by selective area metalorganic vapor phase epitaxy (SA‐MOVPE) on GaN/c‐plane sapphire templates with extremely low pattern fill factor and large inter‐hole spacing was studied with scanning electron microscopy (SEM). The optical nanostructure characteristics were investigated by micro‐photoluminescence spectroscopy at room temperature. It was found that sub‐100 nm structures can be fabricated by controlling the growth time and mask opening size. Single nanostructures exhibit more intense luminescence and a red shift of the band edge transition compared to the GaN layer. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Selective Area Metal–Organic Vapor Phase Epitaxy of Nitride Semiconductors for Multicolor Emission

Selective area metal-organic vapor phase epitaxy (SA-MOVPE) allows in-plane control of emission wavelength by tailored width of masks. For InGaN/GaN multiple quantum wells (MQWs), modulation of luminescence wavelength was achieved based on a balance between vapor-phase diffusion of group-III precursors and their surface incorporation. For the basic understanding of the SA-MOVPE of nitride semiconductors, thickness profiles of GaN, InN, AlN, and InGaN layers around relatively wide (>10 mum) masks were investigated. The effective lateral diffusion length D/k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , which is the ratio of the vapor-phase mass diffusivity of a precursor to its surface incorporation rate constant, was extracted for GaN and InN. The value was much larger for InN due to smaller surface incorporation rate. In the SA-MOVPE of InGaN bulk layer at around 800degC, indium incorporation rate seems to be limited by the surface flux of a gallium precursor, resulting in no variation in the indium content. Varied width of the InGaN wells by the existence of masks seems to govern the shift in the luminescence wavelength from InGaN/GaN MQWs. Therefore, design of the thickness distribution of GaN based on the quantitative model is essential to the controlled in-plane color modulation of solid-state lighting devices using SA-MOVPE.

In xGa 1−xAs/InP selective area metal-organic vapor phase epitaxy for non-magnetic semiconductor spintronics

We carried out selective area metal-organic vapor phase epitaxy (SA-MOVPE) of In-rich In x Ga 1− x As/InP modulation-doped heterostructures in an N 2 atmosphere. The aim is to obtain wire structures which exhibit strong spin–orbit coupling without using etching of the heterostructures for their fabrication. The wire geometry was studied as a function of mask opening width. The transport properties were determined at 0.5 K and up to 10 T magnetic field. A clear growth enhancement was confirmed as the initial opening width decreases; thus, the InGaAs as well as the total thicknesses became larger. Moreover, we confirmed the top width saturates in some narrower wires due to geometrically limited growth by facets. Some narrower wires showed high resistivity, which might originate from structural deterioration in In 0.77Ga 0.23As due to the growth enhancement and/or non-uniformity of the parallel wires. On the other hand, wider wires showed Shubnikov–de Haas (SdH) oscillations, which exhibited SdH beating patterns. All in all it is possible to achieve strong spin–orbit coupling in In x Ga 1− x As/InP wires produced by SA-MOVPE.

Optical evidence for Aharonov–Bohm effect in quantum tubes

We present an optical evidence for Aharonov–Bohm (AB) effect in InAs quantum tubes fabricated by a selective area-metal organic vapor phase epitaxy. The oscillations of the photoluminescence peak energies are observed in quantum tubes depending on the magnetic flux through the tube. These oscillations in energies are shown to be due to the AB effect of a charged exciton in a quantum tube by a theory based on the effective-mass approximation.

Non-linear Surface Reaction Kinetics of GaAs MOVPE Explored by Selective Area Growth

Two-dimensional or three-dimensional numerical simulation on growth rate non-uniformity of selective area metalorganic vapor phase epitaxy in sub-millimeter scale can extract real surface kinetics, which is normally hindered by mass transport rate of film precursors. Non-linear surface kinetics is introduced to analyse group-III precursor concentration dependency for the first time and surface reaction rate constant (ksn) of adsorbed species and adsorption equilibrium constant (K) are extracted from GaAs-MOVPE at 575 C. The effect of misorientation angle of GaAs (100) substrate on these kinetic parameters is examined. It is found that ksn is about 3.4×10-5 mol/m2/s independent of the angle, whereas K is 6.9-12×10-5 m3/mol dependent on the angle. The obtained value of ksn can be converted to lifetime of adsorbed species on GaAs surface and it is 0.3 sec. This is mostly the same with gas-phase decomposition rate of trimethylgallium and supports the accuracy of our non-linear kinetic analysis.