Area Metalorganic Chemical Vapor Deposition Research Articles

InGaAs/InP quantum wires grown on silicon with adjustable emission wavelength at telecom bands

We report the growth of vertically stacked InGaAs/InP quantum wires on (001) Si substrates with adjustable room-temperature emission at telecom bands. Based on a self-limiting growth mode in selective area metal–organic chemical vapor deposition, crescent-shaped InGaAs quantum wires with variable dimensions are embedded within InP nano-ridges. With extensive transmission electron microscopy studies, the growth transition and morphology change from quantum wires to ridge quantum wells (QWs) have been revealed. As a result, we are able to decouple the quantum wires from ridge QWs and manipulate their dimensions by scaling the growth time. With minimized lateral dimension and their unique positioning, the InGaAs/InP quantum wires are more immune to dislocations and more efficient in radiative processes, as evidenced by their excellent optical quality at telecom-bands. These promising results thus highlight the potential of combining low-dimensional quantum wire structures with the aspect ratio trapping process for integrating III–V nano-light emitters on mainstream (001) Si substrates.

Optical and Facet-Dependent Carrier Recombination Properties of Hendecafacet InGaN/GaN Microsized Light Emitters

A hendecafacet (HF) microsized light emitter based on an InGaN/GaN multiple quantum well (MQW) is grown via selective area metal–organic chemical vapor deposition. The HF microsized light emitter is found to possess four crystallographic facets, (0001), {1101}, {1122}, and {11–20}. Distinct facet-dependent emission properties, investigated by confocal scanning photoluminescence (PL) and cathodoluminescence (CL) measurements, are found to originate from differences in indium composition and InGaN quantum well thickness of the MQW. Facet-dependent recombination properties, examined by temperature-dependent micro-PL and PL streak images, suggest that the localization energy and nonradiative recombination of carriers at MQW on each facet are varied with the polarization fields and threading dislocations. Besides, scanning time-resolved PL measurements reveal that the recombination lifetime around the edge where different facets meet is shorter than that in the facet regions, implying such nonradiative recom...

Analysis and optimization of the edge effect for III–V nanowire synthesis via selective area metal-organic chemical vapor deposition

Selective Area Metal-Organic Chemical Vapor Deposition (SA-MOCVD) is a promising technique for the scale-up of nanowire fabrication. Our previous study investigated the growth mechanism of SA-MOCVD processes by quantifying contributions from various diffusion sources. However, the edge effect on nanostructure uniformity captured by skirt area diffusion was not quantitatively analyzed. This work further improves our understanding of the process by considering the edge effect as a superposition of skirt area diffusion and “blocking effect” and optimizing the edge effect for uniformity control of nanowire growth. We directly model the blocking effect of nanowires in the process of precursor diffusion from the skirt area to the center of a substrate. The improved model closely captures the distribution of the nanowire length across the substrate. Physical interpretation of the edge effect is provided. With the established model, we provide a method to optimize the width of the skirt area to improve the predicted structural uniformity of SA-MOCVD growth.

Growth Process Modeling of III–V Nanowire Synthesis via Selective Area Metal–Organic Chemical Vapor Deposition

Growth Process Modeling of III–V Nanowire Synthesis via Selective Area Metal–Organic Chemical Vapor Deposition

Growth, structural and optical properties of ternary InGaN nanorods prepared by selective-area metalorganic chemical vapor deposition

Ternary InGaN nanorods were prepared on dielectric-masked nano-holes with selective area metalorganic chemical vapor deposition. To overcome the tendency for random nucleation of GaN at low temperatures, a pulsed growth procedure was introduced to enhance the diffusion length of Ga adatoms on SiO2, resulting in good selectivity at typical temperature ranges for InGaN. Photoluminescence from the InGaN nanorods can be tuned from near ultraviolet (400 nm) to blue-green (∼500 nm). Microstructural properties were characterized by transmission electron microscopy; threading dislocations from the underlying GaN template were terminated at the nanorod/template interface, resulting in dislocation-free nanorods. The height of dislocation-free InGaN nanorods is about 150 nm, which is much larger than the critical thickness for the onset of misfit dislocations in planar InGaN growth with typical thickness of less than 10 nm for an indium composition between 10 and 20%. The composition profile of In along the growth direction was examined by energy dispersive x-ray spectroscopic mapping and line scan. Oscillations of In composition along the growth direction were observed and are likely due to the kinetic competition between In and Ga adatoms. These InGaN nanorods are expected to be useful as templates for growing higher In composition nano-light-emitting diodes.

Toward Optimized Light Utilization in Nanowire Arrays Using Scalable Nanosphere Lithography and Selected Area Growth

Vertically aligned, catalyst-free semiconducting nanowires hold great potential for photovoltaic applications, in which achieving scalable synthesis and optimized optical absorption simultaneously is critical. Here, we report combining nanosphere lithography (NSL) and selected area metal-organic chemical vapor deposition (SA-MOCVD) for the first time for scalable synthesis of vertically aligned gallium arsenide nanowire arrays, and surprisingly, we show that such nanowire arrays with patterning defects due to NSL can be as good as highly ordered nanowire arrays in terms of optical absorption and reflection. Wafer-scale patterning for nanowire synthesis was done using a polystyrene nanosphere template as a mask. Nanowires grown from substrates patterned by NSL show similar structural features to those patterned using electron beam lithography (EBL). Reflection of photons from the NSL-patterned nanowire array was used as a measure of the effect of defects present in the structure. Experimentally, we show that GaAs nanowires as short as 130 nm show reflection of <10% over the visible range of the solar spectrum. Our results indicate that a highly ordered nanowire structure is not necessary: despite the "defects" present in NSL-patterned nanowire arrays, their optical performance is similar to "defect-free" structures patterned by more costly, time-consuming EBL methods. Our scalable approach for synthesis of vertical semiconducting nanowires can have application in high-throughput and low-cost optoelectronic devices, including solar cells.

Simulation and design of the emission wavelength of multiple quantum well structures fabricated by selective area metalorganic chemical vapor deposition

Selective area metalorganic chemical vapor deposition (SA-MOCVD) is effective for the monolithic integration of semiconductor optical devices. Using appropriate patterns of SiO 2 masks on a substrate, we can fabricate multiple quantum wells (MQWs) of In 1− x Ga x As y P 1− y alloys with various emission wavelengths. Therefore, we can fabricate both passive elements and active components for different wavelengths on a substrate by a single growth. To make the best use of this SA-MOCVD process, we need a simulation tool that predicts the performance of the grown layer for a given mask pattern. We constructed a simulation that predicts the emission wavelength of MQW structures grown by SA-MOCVD. The simulation took into account the gas-phase diffusion of the precursors of In and Ga and their incorporation to the growth area. The rate parameters of these processes were extracted from the growth-rate profile in the SA-MOCVD of InP and GaAs. Based on these data, we simulated the photoluminescence (PL) peak wavelength of (1) In 1− x Ga x As y P 1− y bulk films and (2) MQWs consisting of these quaternary alloys. The simulated results agreed with experimental results, indicating the feasibility of computer-assisted design (CAD) of the mask patterns for SA-MOCVD.

Room-temperature operation of patterned quantum-dot lasers fabricated by electron beam lithography and selective area metal-organic chemical vapor deposition

We have developed a quantum-dot fabrication process which allows for explicit definition of the location and lateral dimension of quantum dots using electron beam lithography and selective area metal-organic chemical vapor deposition. We have demonstrated the first reported room-temperature operation of a patterned quantum-dot edge-emitting laser based on this fabrication technique.

Area-controlled growth of InAs quantum dots and improvement of density and size distribution

We propose and demonstrate a scheme (area-controlled growth) for controlling where self-assembled InAs quantum dots form, using a SiO2 mask and selective area metalorganic chemical vapor deposition growth. Using this technique, quantum dots can be formed in only selected areas of a growth plane. However, in the regions where dots are formed there is variation of dot density and size along the mask stripe direction because of the diffusion of species in the vapor phase. We achieve more uniform distributions of dot density and size by changing the mask pattern. Using this growth technique, it is possible to fabricate integrated optical devices containing an external reflector together with quantum dots serving as the active layer of a semiconductor laser.

Formation of macroscopic steps during selective area metalorganic chemical vapor deposition on GaAs (0 0 1) vicinal substrates

We have investigated the influence of substrate misorientation on facet formation in selective area metalorganic chemical vapor deposition (MOCVD) on GaAs (0 0 1) vicinal substrates. Macroscopic steps several hundred angstroms high were generated on the epitaxial layer over triangular voids where the voids were formed using the conditions of the reverse-mesa-shaped facets. AFM observations of the steps revealed that the exact (0 0 1) crystallographic surface developed on the side for which the (0 0 1) surface is exposed since the surface energy of a low index plane was lower than that of a misoriented high index plane. The wide terrace width of 1100 Å was also observed, which was evidence for the step flow mode growth. Periodic steps were generated over the periodic stripe masks and their potential application to quantum wire fabrication was discussed briefly.

Selective area growth of GaP on Si by MOCVD

Single crystals of GaP were grown on 4° miscut (100) Si substrates by selective area metalorganic chemical vapor deposition. Silicon nitride patterns were used to mask the wafer; no GaP nucleated on the silicon nitride patterns. The top and side walls of the selectively grown GaP stripes (3 μm width) seem to be the (100) and (111) crystal planes. Cross-sectional TEM analysis revealed a smooth GaPSi interface. Focused Raman spectroscopy with a spatial resolution of ∼ 1 μm was used to assess the crystal quality of individual GaP mesas.

Influence of Substrate Misorientation on Facet Formation in Selective Area Metalorganic Chemical Vapor Deposition

AbstractWe have investigated the influence of substrate misorientation on facet formation in selective area metalorganic chemical vapor deposition (MOCVD) on GaAs (001) vicinal substrates. Macroscopic steps several hundred angstroms high were generated on the epitaxial layer over triangular voids where the voids were formed using the conditions of the reverse–mesa–shaped facets. AFM observations revealed that the macroscopic steps were formed by the combined effects of the growth rate enhancement and the development of the exact (001) crystallographic surface. Through removing the growth rate enhancement effect from the experiment results, it could be expected that the exact (001) surface developed only on the side for which the (001) surface was exposed because the surface energy of a low index plane was lower than that of a misoriented high index plane.

A strained-layer InGaAs-GaAs-AlGaAs single quantum well broad spectrum LED by selective-area metalorganic chemical vapor deposition

Three-step selective area metalorganic chemical vapor deposition is used to fabricate strained layer InGaAs-GaAs-AlGaAs single quantum well broad spectrum LEDs. We have fabricated a device with a continuous variation in quantum well thickness along its length by using a tapered oxide width mask for the active region regrowth. A spectral emission width of 80 nm is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-extinction-ratio MQW electroabsorption-modulator integrated DFB laser fabricated by in-plane bandgap energy control technique

The local bandgap energy of an InGaAs/InGaAsP multiple quantum well (MQW) structure was precisely adjusted by in-plane Eg control in one-step selective area metalorganic chemical vapor deposition (MOCVD) growth. The technique was then applied to an MQW electroabsorption-modulator integrated distributed feedback (DFB) laser. Experimental results showed superior device characteristics, such as a high extinction ratio of 25 dB and low threshold current of 15 mA. >

GaAs tetrahedral quantum dots grown by selective area MOCVD

GaAs tetrahedral quantum dots (TQDs) buried in AlGaAs were fabricated using selective area metalorganic chemical vapor deposition (MOCVD). The substrates were SiO 2 masked (111)B GaAs, which were partially etched free of SiO 2 over triangular areas using electron beam lithography and reactive ion etching techniques. First, truncated tetrahedral AlGaAs buffer layers with {110} facet sidewalls were grown over the triangular areas. Next, GaAs TQDs were sequentially grown on top of the AlGaAs. Finally, AlGaAs layers were overgrown on the resulting tetrahedral structures. The height of the GaAs tetrahedrons was estimated to be 20 nm. Photoluminescence of GaAs TQDs buried in AlGaAs was measured at 8.5 K. A clear emission peak from GaAs TQDs was observed at 810 nm. The energy shift from the GaAs emission peak is 19meV, which agrees well with the calculation.

GaAs Quantum Dots by MOCVD

ABSTRACTNew GaAs quantum dots called tetrahedral quantum dots (TQDs) were fabricated using selective area metalorganic chemical vapor deposition (MOCVD). GaAs sub-micron crystals were completely buried in AlGaAs with single growth run without any processing damage at heterojunction interface. The substrates were SiO2 masked (111)B GaAs, which are partially etched free of SiO2 over triangular area using electron beam lithograpy and reactive ion etching techniques. First, truncated tetrahedral AlGaAs buffer layers with {110} facet sidewalls were grown in triangular area. Next, GaAs TQDs were sequentially grown on the top of AlGaAs. Finally, AlGaAs layers were overgrown on the resulting tetrahedral structures. The shape of GaAs tetrahedron was measured by an atomic force microscope(AFM). The size of bottom triangle of GaAs TQDs were estimated to be 20 nm. The size fluctuation was about 2%, which means that uniformity of selective area growth is excellent. Photoluminescence of GaAs TQDs buried in AlGaAs was measured at 8.5K. A clear emission peak from GaAs TQDs was observed at 810 nm. The energy shift from the GaAs emission peak is 19meV, which agrees well with the calculation. The results suggest that the selective area MOCVD method is very promising to fabricate GaAs quantum dots.

GaAs tetrahedral quantum dot structures fabricated using selective area metalorganic chemical vapor deposition

New GaAs quantum dot structures, called tetrahedral quantum dots (TQDs), are proposed to make a zero-dimensional electron-hole system. The TQDs are surrounded by crystallographic facets fabricated using selective area metalorganic chemical vapor deposition (MOCVD) on (111)B GaAs substrates. The calculated energy sublevel structures of zero-dimensional electrons in a GaAs TQD show large quantum size effects, because electrons are confined three dimensionally. GaAs and AlGaAs tetrahedral facet structures on (111)B GaAs substrates partially etched into a triangular shape were grown using MOCVD. Tetrahedral growth with {110} facets occurs in the triangular areas. The cathodoluminescence intensity map for GaAs tetrahedrons buried in AlGaAs shows the tetrahedral dot array.