Selective-area Metalorganic Vapor Phase Epitaxy Research Articles

Fabrication and excitation-power-density-dependent micro-photoluminescence of hexagonalnanopillars with a single InGaAs/GaAs quantum well

Hexagonal nanopillars with a single InGaAs/GaAs quantum well (QW) were fabricated on aGaAs (111)B substrate by selective-area metal–organic vapor phase epitaxy. The standarddeviations in diameter and height of the nanopillars are about 2% and 5%, respectively.Zincblende structure and rotation twins were identified in both the GaAs and the InGaAs layersby electron diffraction. The excitation-power-density-dependent micro-photoluminescence(μ-PL) of the nanopillars was measured at 4.2, 50, 100 and 150 K.It was shown that, with increasing excitation power density, theμ-PL peak’s positions shift to a higher energy, and their intensity and width increase,which were rationalized using a model that includes the effects of piezoelectricity,photon-screening and band-filling. It was also revealed that the rotation twins significantlyreduce the diffusion length of the carriers in the nanopillars, compared to that in theregular semiconductors.

Growth characteristics of GaAs nanowires obtained by selective area metal–organicvapour-phase epitaxy

GaAs nanowires were selectively grown by metal–organic vapour-phase epitaxy within aSiO2 mask window pattern fabricated on a GaAs(111)B substrate surface. The nanowires were100–3000 nm in height and 50–300 nm in diameter. The height decreased as the maskwindow diameter was increased or the growth temperature was increased from 700 to800 °C. The dependence of the nanowire height on the mask window diameter was compared witha calculation, which indicated that the height was inversely proportional to the maskwindow diameter. This suggests that the migration of growth species on the nanowire sidesurface plays a major role. Tetrahedral GaAs grew at an early stage of nanowire growthbut became hexagonal as the growth process continued. The calculated change in Gibbsfree energy for nucleation growth of the crystals indicated that tetrahedra wereenergetically more favourable than hexagons. Transmission and scanning electronmicroscopy analyses of a GaAs nanowire showed that many twins developed along the B direction, suggesting that twins had something to do with the evolution of the nanowireshape from tetrahedron to hexagon.

Formation of InP and InGaAs Air-Hole Arrays on InP(111) Substrates by Selective-Area Metal–Organic Vapor Phase Epitaxy

We report on a promising approach for the formation of compound semiconductor two-dimensional photonic crystal slabs utilizing selective-area metal–organic vapor phase epitaxy (SA-MOVPE). The selective-area growth process for the submicron-sized air holes of InP-based semiconductors was investigated on InP(111)A and (111)B substrates with a periodic array of hexagonal SiO2 masks. By optimizing growth conditions, a highly uniform array of hexagonal air holes in InP and InGaAs with a 500 nm pitch was formed on (111)B substrates. We also fabricated air-hole arrays with InP/InGaAs/InP double heterostructures on InP(111)B, and confirmed photoluminescence from an InGaAs quantum well at low temperatures.

Growth of InGaAs nanowires by selective-area metalorganic vapor phase epitaxy

We studied the growth of InGaAs nanowires on InP(1 1 1)B substrates by selective-area metal organic vapor phase epitaxy (SA-MOVPE). It was found that the initial growth rate of the nanowires depends on the supply ratio of source gas of Ga and In, and it is higher for increasing supply ratio of Ga. At the initial stage, the diameters of the nanowires were almost the same as those of the openings of the mask, indicating that the lateral growth was negligible, while the height of the nanowires increased superlinearly with time. For longer growth time, the diameter of nanowires as well as height increased linearly with time. A possible growth mechanism for such dependence on time and supply ratio of group III source gases is discussed.

Self-assembly and selective-area formation of ferromagnetic MnAs nanoclusters on lattice-mismatched semiconductor surfaces by MOVPE

Abstract The authors report on the self-assembly and the selective-area formation of ferromagnetic MnAs nanoclusters (NCs) on III–V compound semiconductors (1 1 1) B surfaces by metal-organic vapor-phase epitaxy (MOVPE). Hexagonal MnAs NCs with well-defined crystal facets and a high degree of uniformity are self-assembled on planar GaInAs surfaces grown on InP (1 1 1) B substrates. The lateral size and height of typical NCs are 100 and 47 nm, respectively. Lattice images taken by transmission electron microscopy (TEM) show that the top surfaces of the MnAs NCs are atomically flat, and that the interfaces between the NCs and the GaInAs layers are abrupt. We have, in addition, controlled the positions of the MnAs NCs by selective-area MOVPE on GaAs (1 1 1) B substrates partially masked with SiO2 thin films. The hexagonal MnAs NCs do not grow on the SiO2 surfaces, but grow successfully on the GaAs ones, under a relatively high growth temperature condition of 850 °C.

Micro-photoluminescence spectroscopy study of high-quality InP nanowires grown by selective-area metalorganic vapor phase epitaxy

We have investigated the optical properties of single InP nanowires (NWs) grown by selective-area metalorganic vapor phase epitaxy. Systematic measurements on several single NWs revealed that some of they exhibited good optical quality at low temperature. Band gap energy of InP NWs with wurtzite crystal structure was found to be larger by about 88 meV than that of zincblende InP, in good agreement with theoretical prediction.

Observation of Microcavity Modes and Waveguides in InP Nanowires Fabricated by Selective-Area Metalorganic Vapor-Phase Epitaxy

Hexagonal cylindrical InP nanowires with a wurtzite structure were fabricated by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). The microcavity modes and waveguides in InP nanowires were investigated by photoluminesence (PL) spectra. Optical mode analysis for InP nanowires with different lengths reveals the axial Fabry−Perot cavity in InP nanowires, which were formed between the two end facets of nanowires. In addition, T-branch subwavelength guiding and optical coupling in InP nanowires were observed.

Electrical Characterizations of InGaAs Nanowire-Top-Gate Field-Effect Transistors by Selective-Area Metal Organic Vapor Phase Epitaxy

Single InGaAs nanowire-top-gate metal–semiconductor field-effect transistors (MESFETs) were fabricated and characterized. Silicon-doped n-InGaAs nanowires (with a typical diameter of 100 nm) were grown by catalyst-free selective-area metal–organic vapor-phase epitaxy (SA-MOVPE). The FETs of single nanowires on SiO2-coated Si substrates were fabricated by defining metal contacts at both ends of the nanowires and the metal top gate between contacts. According to the measurements of drain current–voltage and gate transfer characteristics, the top-gate MESFETs exhibited significant enhancements in device performance characteristics compared with FETs under back-gate operation; that is, a peak transconductance of 33 mS/mm and a current on–off ratio of 103 were obtained. A possibility for further improvements in FET characteristics was also considered.

Submicron active-passive integration with position and number controlled InAs∕InP (100) quantum dots (1.55μm wavelength region) by selective-area growth

The authors report lateral positioning and number control of InAs quantum dots (QDs) on truncated InP (100) pyramids by selective-area metal organic vapor-phase epitaxy. With reducing QD number, sharp emission peaks are observed from individual and single QDs with wavelength tuned into the 1.55μm telecom region by insertion of ultrathin GaAs interlayers beneath the QDs. Regrowth of a passive waveguide structure around the pyramids establishes submicrometer-scale active-passive integration for efficient microcavity QD nanolasers and single photon sources.

Drain-Current Deep Level Transient Spectroscopy Study of Carrier Emission Process from InAs Quantum Dots in GaAs Narrow-Wire Field Effect Transistors

We studied the states working in the memory operation of GaAs narrow-wire field-effect transistors (FETs) with embedded InAs quantum dots (QDs). The GaAs narrow-wire FETs with a few InAs QDs above the channel were fabricated by selective-area metal organic vapor-phase epitaxy (SA-MOVPE). The drain current, measured by sweeping the gate voltage forward and backward, exhibited clear clockwise hysteresis due to the charging of electrons into the states induced by InAs QDs with a threshold voltage shift (ΔVth) of 30 mV at 20 K. To better understand the mechanism of this memory operation, we studied the traps concerning the InAs QDs by drain-current deep-level transient spectroscopy (DLTS). Peaks representing three kinds of electron traps concerning InAs QDs were observed in the DLTS spectra. These peaks exhibited different dependences on the applied gate pulsed voltage during the DLTS measurement. In comparison with the temperature dependence of ΔVth, we found that our memory operation was attributed to one localized state introduced by InAs QDs.

Selective-area growth of hexagonal nanopillars with single InGaAs/GaAs quantum wells onGaAs(111)B substrate and their temperature-dependent photoluminescence

We report on the fabrication of highly uniform hexagonal nanopillars with singleInGaAs/GaAs quantum wells (QW) on GaAs(111)B substrate by selective-areametal–organic vapour phase epitaxy. The standard size deviation of the fabricatednanopillars with single InGaAs/GaAs QW is about 2% and the standard deviation in theirheight about 5%. With a decrease in temperature, the peak position shifts to shorterwavelength, the peak intensity increases and the peak width decreases. The calculated wellwidth based on the finite square potential well model taking account of the strain effectand the piezoelectric effect is smaller than the value determined from the growthrate and the growth time, which is mainly due to indium segregation and itsincorporation into the subsequent GaAs layer grown at the higher temperature.

選択成長マイクロファセットを用いたGaN系面発光型レーザー

GaN microfacets have been grown by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and applied to GaN-based surface-emitting lasers. The crystal orientation of the microfacets was strictly controlled by the shapes of the mask-openings and growth conditions so that vertical and inclined microfacets were obtained. Hexagonal microprisms (HMPs) of GaN with 5-50μm in diameters have extremely smooth vertical side walls of GaN {10 1 0} microfacets. These GaN HMPs lase by optical pumping and have the inscribed hexagonal optical paths. Additionally, GaN-based horizontal cavity surface-emitting lasers (HCSELs) were successfully fabricated. The GaN-based HCSELs have Fabry-Perot cavity and outer micromirrors, which consist of SA-MOVPE grown {11 2 0} vertical and {11 2 2} inclined microfacets, and lased at room temperature by pulsed current injection. The laser beam emitted laterally from a Fabry-Perot cavity {11 2 0} vertical micromirror is reflected by a {11 2 2} inclined outer micromirror so as to be directed upward. The GaN-based HCSEL has a current-confining structure because the incorporation probability of p-type dopants (Mg) is strongly influenced by facet orientation (growth direction).

Mechanism of catalyst-free growth of GaAs nanowires by selective area MOVPE

We studied the growth mechanism of GaAs nanowires in selective-area metalorganic vapor phase epitaxy (MOVPE) by investigating the dependences on substrate orientations and growth conditions. The nanowire structures were formed only on GaAs (1 1 1)B substrate under high temperature (750 °C) and low arsine partial pressure conditions. Structures selectively grown on substrates with various orientations always exhibited specific low-index facets such as {1 1 0}, {1 1 1}A, and {1 1 1}B. It was also found that the appearance of these facets depended strongly on the growth conditions. Furthermore, we have observed a considerable lateral growth on the sidewalls of the nanowires when the growth temperature was lowered and arsine partial pressure was increased, indicating that the growth mode could be changed by the growth conditions. These results demonstrate that the growth mechanism of GaAs nanowires by SA-MOVPE is neither catalyst nor oxide assisted but by the formation of facets during growth.

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.

Growth of highly uniform InAs nanowire arrays by selective-area MOVPE

We report on size, shape, and position-controlled growth of high-density InAs nanowire array on InAs (1 1 1)B substrates by selective-area metalorganic vapor phase epitaxy (SA-MOVPE). In the optimized growth condition, uniform array of vertically aligned nanowires were formed. Growth carried under different growth temperatures, T G, indicated that the lateral growth along the 〈 1 ¯ 1 0 〉 directions was suppressed for T G⩾540 °C to uniform array of thin InAs nanowires. This behavior is thought to be due to decreased number of bonds available for binding In atoms at step sites via desorption of As adatoms as growth temperature increased. Average height of the InAs nanowires found to depend significantly on the diameter of nanowires.

Lateral wavelength control of InAs∕InGaAsP∕InP (100) quantum dots in the 1.55μm region by selective-area metal organic vapor-phase epitaxy

We report lateral wavelength control of InAs quantum dots (QDs) embedded in InGaAsP on InP (100) substrates by selective-area metal organic vapor-phase epitaxy (SA MOVPE). The technologically important 1.55μm telecommunications wavelength region is assessed by the combination of ultrathin GaAs interlayers beneath the QDs with proper SiNx mask design. Atomic force microscopy and microphotoluminescence reveal evolution of the QDs formed by 2 ML InAs as a function of growth rate enhancement with pronounced height and density increase, resulting in a wide wavelength tuning range of 110nm. Saturation of QD formation is observed for 3 ML InAs supply producing a much smaller tuning range of only 25nm which is supported by the increasing GaAs interlayer thickness. Hence, two regimes are identified allowing either wide wavelength tuning or wavelength stability of QDs in the 1.55μm region offering complementary applications of the monolithic integration of optoelectronic devices by SA MOVPE.

Reactor-scale uniformity of selective-area performance in InGaAsP system

Selective-area metal organic vapor phase epitaxy (SA-MOVPE) of InGaAsP-related semiconductors is one of the most important fabrication techniques for monolithically integrated optical devices. However, it has not been clarified how much the mask effect depends on the position of a wafer in a MOVPE reactor. Therefore, the uniformity of the mask effect in a reactor was investigated experimentally coupled with the simulation in both reactor scale and micrometer scale. As for the reactor-scale distributions of an InGaAsP layer, the measured profiles of the growth rate and composition were well-reproduced by the simulation that assumed the adsorption and the desorption of As and P species. As for the micro-scale distribution in the selective-area growth, the modulations of photoluminescence (PL) wavelength due to masks were dependent on the position of the substrate in the reactor. The reason was assumed to be that the surface reaction rate constant of a precursor had the distribution in the reactor, due to the concentration distribution of both precursors and reaction products.

Photonic crystal slabs with hexagonal air holes fabricated by selective area metal organic vapor phase epitaxy

It is shown that the photonic crystal slab (PCS) with hexagonal air holes has band gaps in the guided mode spectrum, which can be compared to that of the PCS with circular air holes, thus it is also a good candidate to be used for the PC devices. The PC with hexagonal air holes and a = 0.5 μm and r = 0.15 μm was fabricated successfully by selective area metal organic vapor phase epitaxy (SA-MOVPE). The vertical and smooth sidewalls are formed and the uniformity is very good. The same process was also used to fabricate a hexagonal air hole array with the width of 0.1 μm successfully. The air-bridge PCS with hexagonal air holes and a = 0.3 μm and r = 0.09 μm was also fabricated successfully by SA-MOVPE. Further optimization of the growth conditions for the sacrificial layer and the selective etching of the GaAs cap layer is also needed. Our experimental results indicate that SA-MOVPE is a promising method for fabricating PC devices and photonic nanostructures.

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.

Fabrication of one-dimensional GaAs channel-coupled InAs quantum dot memory device by selective-area metal-organic vapor phase epitaxy

Narrow wirelike openings were defined on SiO2-masked GaAs (001) substrates by electron-beam lithography and wet chemical etching methods. A one-dimensional GaAs channel-coupled InAs quantum dot memory device was fabricated in this opened area by the selective-area metal-organic vapor phase epitaxy. Drain current measurement by sweeping the gate voltage forward and backward showed clear hysteresis up to 180K due to electrons charging into the quantum dots with a threshold voltage difference (ΔVth) of 165mV at 20K and 29mV at 180K. Comparison of experimental ΔVth values with the theoretically calculated ones showed that around 300 and 50 electrons were responsible for the memory operation at 20 and 180K, respectively. Real time measurements showed that the write/erase states of the memory device were discriminated for more than 5min at 20K and about 100s at 77K.