Selective Area Metalorganic Chemical Vapor Research Articles

Spectral and threshold performance of patterned quantum dot lasers

Semiconductor quantum dots have been widely researched as a means of improving the performance of optoelectronic devices. Self-assembly has been the dominant method of fabricating quantum dots because of its relative ease compared to more explicit techniques. We have developed a method for fabricating quantum dots in a more explicit manner using electron beam lithography and selective-area metal-organic chemical vapor deposition crystal growth. By eliminating the dependence on strain-driven self-assembly, we can avoid the size distribution and resulting inhomogeneously broadened emission spectrum associated with self-assembled quantum dot ensembles. We report on the threshold and spectral properties of patterned quantum dot lasers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Strained-layer InGaAs-GaAs-InGaP buried-heterostructure quantum-well lasers on a low-composition InGaAs substrate by selective-area MOCVD

Aluminum-free buried-heterostructure quantum-well lasers have been successfully fabricated on low-composition InGaAs substrates. Selective-area metalorganic chemical vapor deposition (MOCVD) was utilized to investigate a variety of InGaAs quantum wells with a wide range of composition and thickness. Compressively strained quantum wells can be deposited thicker on substrates of InGaAs than GaAs before the generation of misfit dislocations. These deeper potential wells enable laser diodes with longer wavelengths (1.1504 /spl mu/m) than GaAs-based emitters and higher characteristic temperatures (145 K) than InP-based devices.

GaN field emitter array diode with integrated anode

GaN field emission pyramids are grown by self-limiting, selective-area metalorganic chemical vapor deposition. The self-limitation provides the potential of high uniformity of the pyramids and the selective-area growth allows one to define regular arrays of GaN pyramids for field emitter arrays (FEAs). Fabrication of an integrated anode lowered the operating voltage of the FEAs by narrowing the anode-cathode distance compared to devices with an external anode. A maximum emission current of 0.15 μA/tip has been observed for voltages of 570 V with an emitter-anode separation of 2 μm.

Progress in InGaAs-GaAs selective-area MOCVD toward photonic integrated circuits

The progress toward integrated photonic devices by selective-area metalorganic chemical vapor deposition (MOCVD) is reviewed. Processing steps involved with fabricating buried heterostructures (BHs) by a three-step technique are outlined, and a computational model is presented that predicts the enhancement behavior of selective-area MOCVD. Results are reviewed for several discrete and integrated photonic devices. These include low-threshold BH lasers, laser diodes integrated with either intracavity or external cavity modulators, dual-channel emitters integrated with both modulators and passive y-junction waveguides, and broad-band light-emitting diodes (LEDs).

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.

Characteristics of GaN stripes grown by selective-area metalorganic chemical vapor deposition

We report on the selective-area metalorganic chemical vapor deposition of GaN stripes in the size range of 50 to 125 urn and the characterization of the morphology, topography, and optical properties of these stripes. GaN films (∼1–3 μm) grown on (0001) sapphire are used as the substrates. Excellent surface morphology is achieved under optimized growth conditions which include a higher V/III ratio than broad area growth. It is found that, under certain growth conditions, (0001) terraces of ~5 µm in width develop at the edges of all stripes, independent of stripe size and orientation. The selectively grown GaN yields stronger band-edge emission than the “substrate” GaN which indicates an improvement in optical quality. However, the donor-acceptor pair recombination (or conduction band to acceptor transition) and yellow emission are also enhanced in certain areas of the stripes. The spatial correlation of these emission bands is established by cathodoluminescence wavelength imaging, and the origin of these emissions is speculated.

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.

Selective-area regrowth of GaN field emission tips

Field emission current has been observed for the first time from GaN. Single-crystal GaN pyramids were grown in arrays by selective-area metalorganic chemical vapor deposition (MOCVD) on GaN thin films using a dielectric mask. GaN does not deposit on the dielectric mask and growth of hexagonal pyramid structures occurs only in mask openings. The pyramids were biased negatively with respect to a metal anode and an emission current of 0.8 μA at 2000 V was observed.

A dual-wavelength source with monolithically integrated electroabsorption modulators and Y-junction coupler by selective-area MOCVD

Three-step selective-area metal-organic chemical vapor deposition (MOCVD) is used to fabricate a dual wavelength InGaAs-GaAs-AlGaAs quantum well laser source with integrated electroabsorption modulators and a passive Y-junction coupler. Threshold current values of 9.5 and 10.1 mA are obtained for two distinct wavelength sources operating continuous-wave (CW) coupled into the same output waveguide.

Selective-area MOCVD growth for 1.3 μm laser diodes with a monolithically integrated waveguide lens

A tapered thickness profile and a high thickness enhancement ratio of 3.5 in the waveguide which are necessary for a narrow beam have been realized by selective-area metalorganic chemical vapor deposition (MOCVD) growth using a tapered shape twin mask. A multiple quantum well (MQW) active layer with high strain of 0.9% which is effective for a low threshold current has also been successfully grown by the control of the compositional modulation of InGaAsP in the selective-area growth. Using these techniques, a narrow beam and a low threshold current have been realized for a 1.3 μm laser diode monolithically integrated with a tapered thickness waveguide lens.

Lateral inhomogeneity in InGaAs–GaAs quantum wire arrays by selective-area metalorganic chemical vapor deposition

We present an experimental characterization of InGaAs–GaAs quantum wire arrays grown by selective-area metalorganic chemical vapor deposition (MOCVD). The wire patterns studied were obtained by high-resolution electron-beam lithography on poly(methylmethacrylate) and wet etching of silicon dioxide. We observe a large nonlinear enhancement of growth inside the wire region. In addition, the results of gas phase diffusion growth simulations on the expected inhomogeneity of the fabricated quantum wires are presented. The degree of inhomogeneity of fabricated quantum wire arrays was studied by spatially resolved photoluminescence. Our results show that a suitable patterning technique, coupled with proper growth conditions, could allow control of the selective growth profile across the wire array.

New Fabrication Technology for Integrating Field Effect Transistors and Diodes

We demonstrated a new integration technology for field effect transistors (FETs) and diodes. This technology uses selective-area metalorganic chemical vapor deposition (MOCVD) for FET and diode layers. FETs (called FECFET) fabricated by this technology have very short distances between the drain and source, so that the characteristics such as knee voltage and transconductance are superior to those of conventional FETs with the same gate length. Because this structure has an n+-doped contact layer under an n-doped active layer, it is easy to integrate with a high-quality diode having low series resistance. By this approach, diodes with low series resistance and low junction capacitance have been fabricated. To demonstrate the integration of the diode and FECFET, a 36 GHz single balanced diode mixer and an intermediate frequency (IF) amplifier have been fabricated on a GaAs wafer.

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.

Growth, characterization, and modeling of ternary InGaAs-GaAs quantum wells by selective-area metalorganic chemical vapor deposition

A computational diffusion model is used to predict thickness and composition profiles of ternary InxGa1-xAs quantum wells grown by selective-area, atmospheric pressure metalorganic chemical vapor deposition (MOCVD), and its accuracy is investigated. The model utilizes diffusion equations and boundary conditions derived from basic MOCVD theory, with reaction parameters derived from experimental results, to predict the concentration of each column III constituent throughout the concentration boundary layer. Solutions to these equations are found using the two-dimensional, finite element method. The growth thickness profiles of GaAs, InP, and InxGa1-xAs deposited by selective-area MOCVD are observed by conventional profilometry, and compositions are measured indirectly by laser emission wavelengths. The data presented show that the model accurately predicts growth thickness and composition profiles of ternary III-V materials grown by selective-area MOCVD.

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>

Dual-channel strained-layer in GaAs-GaAs-AlGaAs WDM source with integrated coupler by selective-area MOCVD

Selective-area metalorganic chemical vapor deposition is used to fabricate a dual-channel strained-layer InGaAs-GaAs-AlGaAs WDM source with integrated coupler. Threshold currents of 11.5 mA were obtained for 1100 μm long uncoated channels operating cw at room temperature. Both channels can be coupled into a single mode fiber without the need for an external coupler.

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>