Area Metalorganic Vapor Phase Epitaxy Research Articles

Non-linear kinetic analysis on GaAs selective area MOVPE combined with macro-scale analysis to extract major reaction mechanism

Numerical simulation on growth rate non-uniformity of selective area growth (SAG) in sub-millimeter scale can extract real surface kinetics in metal organic vapor phase epitaxy (MOVPE) process, which is normally hindered by mass transport rate of film precursors. SAG analysis with non-linear surface kinetics is introduced for the first time to analyze group-III precursor partial pressure dependency of GaAs-MOVPE. Important kinetic parameters, surface reaction rate constant, adsorption equilibrium constant and surface coverage, have been extracted and examined as various substrate misorientation angles. Such non-linear kinetic analysis using SAG (micro analysis) is combined with computational fluid dynamics (CFD) reactor-scale analysis (macro analysis) to elucidate the main reaction mechanism of GaAs-MOVPE process in the whole reactor. The reaction mechanism is different in different parts of the reactor. That means, we should use various kinetic parameters to preciously predict the growth procedure in the whole large-scale reactor.

Fabrication of InP∕InAs∕InP core-multishell heterostructure nanowires by selective area metalorganic vapor phase epitaxy

We report the growth of InP∕InAs∕InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.

Realization of conductive InAs nanotubes based on lattice-mismatched InP∕InAs core-shell nanowires

We report the realization of ordered arrays of single-crystalline InAs nanotubes by a simple pure-eptiaxial approach. The process involved the fabrication of lattice-mismatched InP∕InAs core-shell nanowires using selective area metalorganic vapor phase epitaxy on InP (111)A substrates. The subsequent removal of the InP core resulted in vertically aligned InAs nanotubes which were highly uniform with well-defined features and controllable dimensions. Transmission electron microscopy studies confirmed that the nanotubes were single-crystalline with wurtzite crystal structure and temperature-dependent transport measurements revealed that they were conductive without any intentional doping. The realization of such conductive InAs nanotubes opens up new possibilities for both fundamental studies and future device applications.

Role of surface diffusion during selective area MOVPE growth of InP

Selective Area Metalorganic Vapor Phase Epitaxy (SA-MOVPE) growth of compound semiconductor, such as In 1– x Ga x As y P 1– y , is an indispensable technology to realize one-step fabrication of monolithic optical integrated circuits (OEICs). In SA-MOVPE, the growth rate of unmasked region is enhanced, because un-reacted group III precursors on the mask region diffuse into the epitaxial growth region. This growth rate enhancement is mainly caused by the gas-phase diffusion of precursors, but the contribution of surface diffusion becomes larger as the unmasked stripe becomes narrower. Moreover, in the SA-MOVPE growth of InP, the abnormal growth near the mask edge and the formation of tear-drop-like hillocks, which is considered to be originated from surface diffusion, are observed. In this work, the role of surface diffusion during SA-MOVPE growth of InP was investigated by measuring the cross-sectional area of abnormal growth and surface roughness. By changing the growth temperature from 793 K to 883 K, the area of abnormal growth increased and took maxima at 823 K, and decreased again at higher temperature. The concentration of group III precursor enhanced the abnormal growth and the roughness. The concentration effect was larger than the first order, and its relation to the surface diffusion length was suggested. This information on surface diffusion during SA-MOVPE is a key factor for the precise control of SA-MOVPE growth.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (1 1 1)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO 2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {1 1 0} vertical facets with their diameter of order of 100 nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60 nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (111)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 100nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Realization of InAs-based two-dimensional artificial lattice by selective area metalorganic vapor-phase epitaxy

The experimental realization of two-dimensional semiconductor artificial lattice based on InAs quantum wires is reported here. Artificial Kagome lattice fabricated using InAs quantum wires of unit cell size 0.7 μm has been theoretically proved to show ferromagnetism. Fabrication of such a structure with InAs quantum wires was attempted by selective area metalorganic vapor phase epitaxy using GaAs (111)A substrates. Temperature-dependent growth mode change was observed and Volmer-Weber growth mode at high temperature inhibited the formation of uniform structure. Low temperature and low AsH3 partial pressure resulted in the successful fabrication of 0.7 μm period InAs-based Kagome lattice structure.

The effect of group V precursor on selective area MOVPE of InP/GaAs-related materials

Tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBAs) are widely used as alternative group V precursors for phosphine and arsine, mainly because of their comparatively low toxicity and low decomposition temperature. In this work, the effect of group V precursors on selective area metal-organic vapor phase epitaxy (MOVPE) of InP/GaAs-related materials was studied, in terms of the surface sticking probabilities of group III intermediates. The sticking probabilities were measured by analyzing the thickness profiles of selectively grown films of GaAs and InP in 380-μm-wide growth area between SiO 2 masks. The sticking probability of the In precursor was about 3.2 times larger in the growth with PH 3 than with TBP at 823 K. The sticking probability of the Ga precursor was nearly the same whether the group V source was AsH 3 or TBAs. Such differences were manifested in the In/Ga ratio of selectively grown In x Ga 1− x P. The difference in the sticking probabilities between the precursors of In and Ga mainly determined the In/Ga ratio. Based on a linear combination model using measured values of sticking probabilities, the variation of the composition was predicted to be larger in the growth with phosphine than with TBP. Measurement of the In/Ga composition using electron-probe micro analysis confirmed that prediction. It was proved that the kind of group V precursor is an important factor that governs composition uniformity in selective area MOVPE.

Fabrication of semiconductor Kagome lattice structure by selective area metalorganic vapor phase epitaxy

Artificial two-dimensional semiconductor Kagome lattice structures formed by quantum wires can show ferromagnetism when the flatband is half filled, even though it does not have any magnetic elements. Experimental realization of such a Kagome lattice structure is reported. The structure, with different pattern periods, was formed with GaAs quantum wires by selective area metalorganic vapor phase epitaxy on GaAs (111)B substrates. To overcome the lateral overgrowth and to improve the shape of smaller period pattern, flow rate modulation epitaxy was employed and a GaAs Kagome lattice structure with 1 μm period was effectively grown.

Formation and characteristics of 100-nm scale GaAs quantum wires by selective area MOVPE

We fabricated quantum wires (QWRs) with sub-micron wire width using GaAs/AlGaAs selectively doped structures grown by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (0 0 1) masked GaAs substrates partially covered by SiON. From the measurement of a two-terminal conductance as a function of geometrical wire width, QWRs with effective channel width <100 nm are formed without application of any gate bias. The magnetoresistance measurement at 1.7 K also suggests the formation of narrow QWRs, although it also indicates a presence of potential fluctuation along the QWRs. The effective channel width of present QWRs are much narrower than the previously reported values (∼300 nm) of those formed by SA-MOVPE.

Growth and Optical Properties of 2D Photonic Crystals Based on Hexagonal GaAs/AlGaAs Pillar Arrays by Selective-Area Metalorganic Vapor Phase Epitaxy

ABSTRACTWe report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar arrays using selective area (SA) metalorganic vapor phase epitaxy (MOVPE) for the application of two-dimensional photonic crystals (2D-PhCs). SA-MOVPE was carried out on SiO2 masked (111)B GaAs substrates with circular or hexagonal hole openings. Extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 200 nm were obtained. Unexpectingly strong intense light emission was observed for the room temperature photoluminescence measurement, which suggests low surface nonradiative recombination and enhancement of the light extraction efficiency of the pillar arrays.

Fabrication of single- or double-row aligned self-assembled quantum dots by utilizing SiO2-patterned vicinal (001) GaAs substrates

We investigated the formation of In0.8Ga0.2As self-assembled quantum dots (SAQDs) grown on SiO2-patterned 1°, 2°, and 5°-off (001) GaAs substrates by selective area metalorganic vapor phase epitaxy technique. The SiO2 patterns were filled with various stripe opening windows along the misorientation direction of the substrates. During the growth of the GaAs buffer layer on the opening regions, the steps on the (001) top facet was affected by the widths of the (001) top facet and the misorientation angles of the substrates. Single- or double-row aligned In0.8Ga0.2As SAQDs having definite interval were successfully fabricated on the (001) top facet with optimized top width and periodicity of step bunching. These results indicate that the selective growth technique of SAQDs by utilizing SiO2-patterned vicinal substrates is promising for nanoelectronic device applications such as single-electron memory devices.

Two-way current switch using Coulomb blockade in GaAs quantum dots by selective area metalorganic vapor phase epitaxy

We fabricated a two-way current switch by selective area metalorganic vapor phase epitaxy and showed their characteristics as path switch based on a Coulomb blockade phenomena. Two-way current switch was realized by integrating two quantum dot (QD) devices having two types (control/main) of gate electrodes. Coulomb oscillation were observed as a function of both control and main gate voltage in each QD-devices (QDDs). It was also found that the phase of the Coulomb oscillations for the main gate could be controlled by tuning the control gate voltage. We demonstrated the switching between two current paths at appropriate bias conditions where Coulomb oscillation of two QDDs was complementary.

Low temperature transport in dual-gated SETs fabricated by selective area metalorganic vapor phase epitaxy

We describe transport measurements in a novel dual-gated single electron transistor based on a quantum dot (QD) fabricated by selective area growth of metalorganic vapor phase epitaxy. We observed, for the first time, clear Coulomb oscillations fabricated in combination with direct growth and lithographically defined metal gates, and achieved nearly independent control of the QD potential and the tunneling barrier height. We also were able to observe a signature of Kondo resonance when the coupling between leads and a quantum dot was sufficiently strong.

GaAs dot-wire coupled structures grown by selective area metalorganic vapor phase epitaxy and their application to single electron devices

We describe a method for fabricating GaAs dot arrays and dot-wire coupled structures having periodic nanofacets which uses selective area metalorganic vapor phase epitaxy. First, a thin GaAs buffer layer and an AlGaAs layer are grown on a masked substrate having wirelike openings with periodic width modulation. The width of AlGaAs wirelike structure is naturally squeezed by the periodic combination of nanofacets, and its top (001) surface is partially isolated by a self-limited region. Next, an AlGaAs/GaAs quantum well structure is fabricated on the substrate to form dots on the narrower top terraces, wires on the wider terraces, and ridge wires in the self-limited region. Cathodoluminescence images clearly showed dot arrays and dot-wire coupled structures were formed using this method. A single electron transistor with the same structure was also fabricated, and clear Coulomb blockade oscillation was observed. We also describe single electron tunneling devices with these dot arrays and dot-wire coupled structures.

Selective area metalorganic vapor phase epitaxy of thick crack-free GaN films on trenched SiC substrates

Crack-free GaN films up to 11-μm-thick have been grown by using trenched SiC substrates and selective area metalorganic vapor phase epitaxy. These crack-free GaN films have hexagonal shapes and are surrounded by trenches. 97% of the hexagonal GaN films with side lengths of 100 μm and thickness of 11 μm was crack-free. The GaN films do not crack because the lateral propagation of cracks stops at the trenches and strain is relaxed in the small-area hexagonal GaN. This strain relaxation is confirmed by micro-Raman scattering measurements and agrees well with theoretical predictions.

Optical Anisotropy in InAs Quantum Dots Formed on GaAs Pyramids

In this paper, we present the results of polarization-dependent micro-photoluminescence (µ-PL) measurements of InAs quantum dots (QDs) selectively formed on GaAs pyramidal structures by selective area metalorganic vapor phase epitaxy. Under nonresonant excitation, strong optical anisotropy is observed in the PL spectra of the InAs QDs. Under near-resonant excitation, where the excitation energy is close to the wetting layer luminescence, the linear polarization degree of InAs QD is larger than that observed under nonresonant excitation. When excited and detected lights have the same polarization along two <110> directions, the PL is intense. However, in the cross polarization configurations, the PL intensities are very weak. The observed strong optical anisotropy in InAs QDs formed on GaAs pyramids under nonresonant excitation can be attributed mainly to the asymmetry of the QD potential which results from the anisotropic strain relaxation and shape of QDs, while that under the near-resonant excitation is explained by the hot photoluminescence effect.

Lateral thickness modulation of InGaAs layers on GaAs in selective area metalorganic vapor phase epitaxy

We investigated the lateral thickness modulation of InGaAs layers grown on width-modulated GaAs wire structures in selective area metalorganic vapor phase epitaxy (SA-MOVPE). The InGaAs layer was formed for various GaAs buffer layer thicknesses and growth conditions. Growth of the InGaAs layer was enhanced, which is caused by the atom migration of group III atom from sidewall facets. The result indicates that the lateral thickness modulation along the [1 1 0] direction becomes more abrupt if one suppresses the diffusion on the top (0 0 1) terrace surface and the supply of growth species from sidewall facets in the transition region.

Self-formed quantum nano-structures by selective area MOVPE and their application to GaAs single electron devices

Novel quantum nano-structures which consist of quantum dots connected with quantum wires through tunneling barriers have successfully been fabricated using selective area metalorganic vapor phase epitaxy (SA-MOVPE) and have been applied to form single electron devices. GaAs/AlGaAs modulation doped heterostructures are grown on a GaAs (001) substrate partially masked with SiNx. A quasi-1 dimensional electron gas (Q-1DEG) is formed in a narrow wire-like opening, which has two prominences and a dent to modulate the channel width. From the transport properties, we confirm that a quantum dot and quantum wires connected through tunneling barriers, that is, a single electron transistor structure, is naturally formed in the part of the channel with modulated width. We will discuss the mechanism by which the dot and tunnel barriers are formed by SA-MOVPE.

Formation of single and double self-organized InAs quantum dot by selective area metal-organic vapor phase epitaxy

Position- and number-controlled InAs self-organized quantum dots (SOQDs) were formed by selective-area-metal-organic chemical vapor phase epitaxy on the partially SiNx patterned GaAs (001) substrate. The mask layer was patterned along the [110] direction, and somewhat wider rectangular openings were also attached to the line. As a result of GaAs SA growth, a pyramidal shaped structure was formed on the rectangular region of the pattern. The top area of the pyramidal structure is a very narrow hexagonal-shaped (001) facet which is surrounded by two-{111}B and four-{124} facets. The SOQD was preferentially formed on the top (001) facet because the growth rate on the (001) facet is far much higher than on the surrounding sidewalls. It is found that the number of SOQDs formed is strongly dependent on the width of the top (001)-facet so that control of single, double, and multiple SOQD(s) is possible.