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The growth of high‐crystal‐quality GaAs on InGaP without sacrificing the carrier lifetime and shunt resistance of the InGaP layer is reported, utilizing a 10 nm‐thick low‐temperature‐grown InGaP cover layer (LTGCL). Electronic devices with a GaAs/InGaP heterostructure such as solar cells, high‐electron‐mobility transistors (HEMTs), and lasers have attracted considerable attention because of their superior characteristics compared with conventional homostructure devices. However, the device performance has scope for improvement, particularly, the interface quality. To realize high‐performance GaAs/InGaP heterostructure devices, high‐crystal‐quality GaAs needs to be grown on high‐temperature‐grown InGaP, which has a long carrier lifetime and high shunt resistance. High‐temperature‐grown InGaP, however, has a rough surface, which degrades the crystal quality of the overlying GaAs. To solve this problem, the use of high‐temperature‐grown InGaP with an LTGCL is proposed, which has an atomic‐scale smooth surface. The advantages of using an LTGCL are discussed with a heterostructure solar cell as an example. The findings of this study indicate that the LTGCL can contribute to further improvement of the performance of heterostructure devices. [ABSTRACT FROM AUTHOR]

Precise strain compensation for lattice-mismatched quantum wells is crucial for obtaining high performance devices such as quantum well solar cells. High-accuracy in situ curvature monitoring is a more efficient tool to adjust growth conditions for perfect strain balancing, and we have achieved curvature measurement during growth of InGaAs/GaAsP multiple quantum wells by metal organic vapor phase epitaxy. We have also developed the curvature calculation model taking into account of thermal expansion and lattice relaxation effects based on Stoney's equation. The measured periodical curvature behavior corresponds to the growth of compressive InGaAs well layers and tensile GaAsP barrier layers and fits perfectly with a theoretical curve assuming the structural parameters (thicknesses and atomic contents) obtained by x-ray diffraction analysis, confirming correctness of the developed calculation method. Considering the proper thermal expansion coefficients for InGaAs and GaAsP, we have obtained much accurate fitting results for measured curvature. [ABSTRACT FROM AUTHOR]

Two-dimensional or three-dimensional numerical simulation on growth rate nonuniformity of selective area metallorganic vapor phase epitaxy (SA-MOVPE) in sub-millimeter scale can extract real surface kinetics, which is normally hindered by mass transport rate of film precursors. Nonlinear surface kinetics is introduced to analyze group-Ill precursor concentration dependency of SA-MOVPE 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 (Φ) of GaAs(100) substrate on these kinetic parameters was examined. It was found that ksn is about 3.4 X 10-5 mol m-2 s-1 independent of Φ , whereas K ranged from 6.9 to 12 X 105 m3 mol-1 dependent on Φ. The obtained value of ksn can be converted to lifetime of adsorbed species on GaAs surface and it is 0.3 s. This is mostly the same with gas-phase decomposition rate of trimethylgallium and supports the accuracy of our nonlinear kinetic analysis. [ABSTRACT FROM AUTHOR]

Abstract: In situ anti-oxidation treatment after the growth of GaAs is essential for an ideal interface between GaAs and an Al2O3 gate dielectric, because the arsenic oxide is a major origin of interface states. The growth of AlP epitaxial layer on the top of GaAs was proposed as a novel anti-oxidation passivation method. The AlP layer almost converted to Al2O3 upon air exposure, serving as both a stable anti-oxidation layer and as part of a gate dielectric. Compared with surface passivation with Al by exposure to TMAl (trimethylaluminum), which we have proposed previously, the morphology of the passivated surface, which is a critical factor for the performance of a metal-insulator-semiconductor (MIS) structure, was dramatically improved due to the coexistence of a group-V precursor. For an ideal interface without arsenic oxide, an arsenic-free surface prior to the AlP growth was also required. H2S treatment allowed us to obtain the low-As-content c(8×2) surface reconstruction of GaAs for the first time by MOVPE. Passivation by AlP on the low-As-content c(8×2) surface reconstruction of GaAs has made it possible to obtain an Al2O3/GaAs gate stack which exhibited smooth morphology and complete suppression of arsenic oxide. Reduction of interface states by this passivation was evidenced by the improved photoluminescence intensity from GaAs. [Copyright &y& Elsevier]

Abstract: Kinetic analysis of the surface adsorption layer on GaAs, InAs, InP, and GaP surfaces during metalorganic vapor phase epitaxy (MOVPE) was performed by in situ monitoring of the temporal behavior of surface reconstructions using reflectance anisotropy spectroscopy (RAS). When the flow of group-III sources was switched on/off, the transient RA signal exhibited two time constants t 0 and t 1 in response to the generation/extinction of the adsorption layer. It was considered that t 0, when the supply of group-III sources was started, corresponds to the adsorption of group-III atoms from the gas phase to the adsorption layer, and that t 1, when the supply of group-III sources was terminated, is associated with the incorporation of adsorbed group-III atoms to the crystal. The rate constant of adsorption, 1/t 0, was approximately 2s−1 for all surfaces except for GaP. The rate constant of incorporation, 1/t 1, ranged from 0.1 to 10s−1. It was found that 1/t 1 for the As-containing materials was faster than that for P-related materials, and 1/t 1 for In-containing materials was faster than that for the Ga-containing materials. For the As-containing materials, 1/t 1 agreed with the incorporation rate constants of adsorbed group-III precursors obtained using the Langmuir–Hinshelwood model by the analysis of selective-area growth (SAG). [Copyright &y& Elsevier]

Highlights • The accelerated growth rate of GaAs up to 120 μm/h by MOCVD. • Cell performance of GaAs solar cells grown at 90 μm/h with various V/III ratio. • Demonstration of low deep emission with low-temperature PL characterization. Abstract We present the feasibility of metalorganic vapor phase epitaxy (MOVPE) with extremely high-speed growth of GaAs for solar cell applications. The growth rate was increased up to 120 μm/h, and exhibited an almost linear relationship with the amount of supplied trimethylgallium (TMGa). The thickness variation and doped carrier concentration of GaAs grown at 90 μm/h were comparable to those of conventionally grown GaAs at a lower growth rate. The potential for reducing the V/III supply ratio was investigated to reduce the material cost. Non-doped GaAs wafers were grown at the accelerated growth rate of 90 μm/h, with various V/III ratios. The growth rate of GaAs increased by 20% when the V/III ratio was decreased from 40 to 5. In low temperature photoluminescence (PL) measurement, significant change in PL spectra was not observed, indicating that there was no significant change in quality. The light-power conversion efficiency was almost comparable for V/III ratios from 10 to 40 whereas that at the lowest V/III ratio of 5 was degraded. Photovoltaic (PV) solar cells of GaAs were fabricated with various growth condition. It is found that the performance of the cells grown at 90 μm/h were comparable with previous results. [ABSTRACT FROM AUTHOR]

Highlights • Design criteria of high growth rate MOVPE reactor are described. • GaAs solar cell was grown by MOVPE with a growth rate of 90 µm/h. • The cell efficiency of 23.59%, Voc of 1.003 V, Jsc of 29.36 and FF of 0.81. • Si doped GaN was grown on 4 in. sapphire substrate by production MOVPE. • E3 trap density was about 1 × 1014 cm−3 at a donor concentration of 1.0 × 1016 cm−3. Abstract High growth rate of GaAs more than 90 μm/h is achieved in the attempt of the productivity improvement of solar cells. The design concept is derived from the MOVPE reactor for nitrides. The design criteria for nitride MOVPE reactor were found to be very useful for GaAs MOVPE. Originally, MOVPE reactors for nitrides were developed on the basis of the reactor design for classical III-V materials. Today, the principle of reactor design to cope with the singularity of nitrides brings about essential feedback to the next-generation reactors for classical III-V materials for improved productivity. At first, design criteria for GaN MOVPE reactor are described in light of the vapor phase reaction. Secondly, cost analysis of a 19 µm-thick GaN layer on a bulk GaN substrate for a vertical diode is briefly discussed in light of a trade-off between a high purity and a high growth rate of GaN. In GaAs-based solar cells, the thickness of light absorber is a couple of micrometers, accompanied by a thin (Al)InGaP cap, the growth time of which can be reduced to a few minutes if the growth rate is on the order of a few tens µm/h. In consideration of these factors, cost analysis of MOVPE for GaAs solar cells will be discussed in comparison with GaN on GaN diode. [ABSTRACT FROM AUTHOR]

Realization of high efficiency III-V-on-Si solar cells requires preparation of an oxygen free Si substrate surface, which allows for subsequent antiphase domain free III-V epitaxy. For GaAsP/Si tandem cells, the impact of As on established Si processing in metal organic vapor phase epitaxy (MOVPE) is essential. Here, we study the interaction of As with vicinal Si(100) surfaces, the formation of atomically well-ordered As-modified Si(100) surfaces, and its impact on subsequently grown GaP epilayers. We apply optical in situ spectroscopy during MOVPE and show that process routes strongly affect the formation of double-layer steps on Si(100). We demonstrate that exposure to As, together with HF pre-treatment, enables processing of suitable Si(100) 2° and 6° offcut surfaces at temperatures below 820 °C. Subsequently grown GaP epilayers exhibit smooth surfaces free of antiphase disorder and distinct Laue oscillations in X-ray diffraction. Such low temperature processing, which is controllable in situ , is promising for further metamorphic GaAsP integration. [ABSTRACT FROM AUTHOR]

Crystal properties of low-temperature grown AlN (LT-AlN) combined with low temperature GaN (LT-GaN) grown by metal organic vapor phase epitaxy (MOVPE) were investigated to obtain a high quality GaN/AlN/GaN structure with a few-nm-thick AlN layer. LT-AlN suppresses unintentional Ga incorporation and can be pseudomorphically grown on GaN with a relatively smooth surface morphology. The lattice of LT-AlN coherent to GaN, however, was found to relax after reactor conditions were changed to grow the subsequent GaN layer at higher temperature. The top GaN layer grown on the relaxed LT-AlN, thus, exhibited a rough surface morphology and a threading dislocation density (TDD) higher than 10 9 cm −2 estimated from an X-ray diffraction measurement. An LT-GaN capping layer was found to be highly effective for avoiding such lattice relaxation of LT-AlN. The combination of LT-AlN and LT-GaN enables us to obtain a GaN/AlN/GaN junction with high Al content, a low TDD, and abrupt interfaces. As a result, introducing an LT-GaN layer improved the photoelectrochemical (PEC) property of a polarization engineered un-doped GaN/AlN/n-type GaN (u-GaN/AlN/n-GaN) photocathode for water splitting. [ABSTRACT FROM AUTHOR]

Wire on Well (WoW) structure embedded in a matrix is naturally formed by growing In x Ga 1−x As/GaAs 1−y P y strained multiple quantum wells (MQW) on vicinal substrates and employing triethylgallium (TEGa) as a precursor in low-temperature MOVPE. The structure is useful for the subcell in current-matched mult-junction solar cells with lattice-matched materials because of its ability of band-gap tuning. In this research, high density and uniform In 0.30 Ga 0.70 As/GaAs 0.6 P 0.4 WoW was obtained up to 200 stacks and its structure was analyzed by X-ray diffraction reciprocal space mapping, atomic force microscopy and scanning transmission electron microscopy. The structure of the wire can be controlled by changing the equivalent layer thicknesses of In 0.30 Ga 0.70 As and GaAs 0.6 P 0.4 . The photoluminescence peak from the WoW shifted according to the size of InGaAs wires and the intensity was dependent on the accumulation of lattice-mismatch stress. [ABSTRACT FROM AUTHOR]

In x Ga 1− x As/GaAs 1− y P y strain-balanced superlattice (SL) is a promising narrow-gap material that can be lattice-matched to Ge or GaAs. When growing uniform SLs on vicinal substrates for Ge-based application, formation of step-bunching and the resultant layer undulation is a critical problem. The present paper reports low-temperature metal–organic vapor phase epitaxy (MOVPE) with triethylgallium (TEGa) to improve the stability and the uniformity of SL growth. Using trimetylgallium (TMGa), steps were severely bunched especially during InGaAs growth at high temperature, and the average reflectance of SLs significantly decreased due to lattice relaxation above 580 °C. Lowering the growth temperature to 550–530 °C was effective in order to grow 100-period SLs with a mirror-like surface, but an apparent lateral layer undulation was still confirmed by ex-situ X-ray-diffraction and STEM observation. Growth of SLs below 530 °C with TMGa was found to result in serious crystal degradation due to unstable growth in the kinetically-limited temperature range. In contrast, use of TEGa enabled 100-period SLs to be successfully grown even at lower temperature owing to its efficient pyrolysis process. Highly uniform SLs with negligible layer undulation were grown at 510 °C with TEGa, showing a photoluminescence spectrum which was as sharp as the one for SLs grown on an exact-oriented substrate. The absorption spectra for the SLs grown with TEGa showed similarly sharp edge with a strong exciton peak. [ABSTRACT FROM AUTHOR]

Abstract: Strain-compensated InGaN/AlN MQWs were grown on a c-plane GaN/sapphire template by MOVPE at 780°C. After optimization of its growth conditions, several samples of InGaN/AlN MQWs with varied well and barrier thicknesses were prepared in order to find the best balance of each layer thickness. Strains inside the MQWs were evaluated by reciprocal space mapping (RSM) measurements, and the results were quite consistent with the calculation of strain estimation. Characterization by HRXRD and photoluminescence measurements revealed an impact of strain accumulation on the quality of MQWs, and the best results were obtained in the most strain-compensated InGaN/AlN MQWs. Compared with InGaN/GaN MQWs with the same thicknesses of wells and barriers, InGaN/AlN MQWs proved to have promising characteristics for several optical devices. [Copyright &y& Elsevier]

Abstract: Using high-accuracy in situ curvature measurement during growth of InGaAs/GaAsP strain-compensated multiple quantum wells (MQWs) by metal organic vapor phase epitaxy (MOVPE), we have successfully clarified the effect of hetero-interfaces on strain control in InGaAs/GaAsP strain-balanced MQWs. By analyzing curvature transients and X-ray diffraction (XRD) fringe patterns, we found that an inadequate gas-switching sequence induces unintended atomic content at the interfaces between InGaAs and GaAsP and then influences the average strain of the structure. Through considering the atomic characteristics and measuring the reflectance anisotropy transient during growth, it has been revealed that the optimized stabilization time for arsenic and phosphorus mixture before GaAsP barrier growth should be longer than 3s at 610°C. [Copyright &y& Elsevier]

Abstract: Fabrication of abrupt InGaP on GaAs (InGaP/GaAs) and GaAs on InGaP (GaAs/InGaP) hetero-interfaces has been difficult using metal organic vapor phase epitaxy (MOVPE) due to the exchange of P and As during the fabrication steps. Indium (In) surface segregation during InGaP growth also degrades the abruptness. Here, the MOVPE gas-switching sequence to fabricate atomically abrupt hetero-interfaces was optimized and the effects of this optimization on the hetero-interface abruptness were quantitatively evaluated using the Z-contrast method with scanning transmission electron microscopy (STEM). Results revealed that (a) in the fabrication of InGaP/GaAs hetero-interface, the GaAs top layer should be stabilized using As-source gas supply, and the excess As layer on GaAs should be terminated using an additional supply of Ga species, and (b) in the fabrication of GaAs/InGaP interface, the InGaP layer should be grown using the flow modulation method to suppress In surface segregation. In conclusion, the abruptness of hetero-interfaces of InGaP/GaAs and GaAs/InGaP was improved by using these optimized gas-switching sequences. [Copyright &y& Elsevier]

Abstract: Strain-balanced growth of highly mismatched quantum wells is of crucial importance for obtaining high performance devices such as quantum-well solar cells and quantum cascade lasers. In situ curvature measurement successfully captured strain accumulation in lattice-mismatched InGaAs/GaAsP multiple quantum wells that were grown by metal–organic vapor phase epitaxy. Average strain in the layers was detectable using the slope of curvature versus layer thickness. High-sensitivity measurement made it possible to detect strain accumulation and release within a single layer of InGaAs and GaAsP, respectively, by looking at the see-saw-like oscillation of curvature, which is an indication of successful strain balancing in a period of well/barrier. In situ curvature monitoring makes it easier and more efficient to adjust growth conditions for perfect strain balancing, as compared with conventional repetition of growth and X-ray diffraction measurement. [Copyright &y& Elsevier]

Abstract: Intersubband transition (ISBT) at 1.55μm in AlN/GaN multi quantum wells (MQWs) was realized by metal organic vapor phase epitaxy (MOVPE) using the pulse injection (PI) method to grow GaN well layers at 770°C. It was shown that a main factor for shifting ISBT wavelength to shorter region to cover 1.55μm and improving ISBT properties of MQWs is the growth temperature of MQWs. Best structural and ISBT properties are observed at low growth temperature of 770°C in this study. Carbon incorporation level in GaN layer grown by the PI method (PI-GaN) showed one order smaller value compared with that by the conventional continuous method. Moreover, further decrease in growth temperature to 770°C did not show significant increase in carbon incorporation in PI-GaN layer. It clearly indicates that the PI method is very effective in reducing carbon concentration in GaN layer, especially at low temperature region. The low carbon concentration of 4×1018 cm−3 released by the PI method was indispensable for realizing enough carrier concentration of 1.6×1019 cm−3 to achieve strong ISBT at 1.55μm. [ABSTRACT FROM AUTHOR]

Abstract: A strain-balanced InGaAs/GaAsP multiple quantum-wells (MQWs) structure was grown by metal organic vapor phase epitaxy (MOVPE) on GaAs substrate, aiming at a middle cell that improves current matching in a tandem solar cell. In order to detect the instant of strain relaxation in the course of MOVPE, which deteriorates crystal quality significantly, we employed in situ optical surface reflectivity measurement. When strain balancing was incomplete, surface reflectivity dropped during the growth of MQWs, indicating lattice relaxation. Such drop in surface reflectivity occurred at a smaller number of stacked quantum wells when the absolute value of an average strain per well/barrier pair was larger. The accumulated strain, i.e., the product between the average strain and the total thickness at the moment of reflectivity dropped, was roughly constant for all the MQWs, indicating a possibility that we can use this value as the measure to predict the maximum number of MQWs for a given value of the average strain. The reflectance anisotropy (RA) was also monitored in the course of the growth. The value of RA showed linear periodic behavior before the lattice relaxation, corresponding to the well/barrier stacks, suggesting that anisotropy of surface atoms reflects accumulated strain of the growth surface. [Copyright &y& Elsevier]

Abstract: We have successfully formed a thin twin-free layer on the top of InGaAs micro-discs by multi-step growth using micro-channel selective-area MOVPE on Si(111) substrates. The multi-step growth employs a gas flow sequence in which the partial pressure of the Ga source (trimethylgallium; TMGa) is modulated to control the initial nucleation and the direction of subsequent growth. We have previously improved in-plane uniformity of crystal shape of InGaAs micro-discs by 3-step growth that starts with InAs nucleation. Using these micro-discs as templates, InGaAs with tripled partial pressure of TMGa was grown as the fourth step. The growth of this fourth layer on the disc surface seems to suppress the layer-by-layer growth on the (111) plane and to terminate rotational twins, as well as keeping the size deviation of micro-discs under 25%. One of the most laterally grown micro-discs (with thickness of 380nm and width of 7.1μm) had a 50-nm-thick twin-free layer on the top. [Copyright &y& Elsevier]

Abstract: We have investigated the initial growth of InAs on Si(111) substrates produced with metal-organic vapor phase epitaxy (MOVPE) and using micro-channel selective area growth (MC-SAG). Treatment of the Si surface prior to InAs growth is essential in order to achieve high-yield nucleation of a single island in each growth area. A breakthrough for successful nucleation was the use of tertiarybutylphosphine (TBP) pre-flow. We have analyzed the effect of such surface pretreatment in terms of the shape of InAs islands at the initial stage of growth and the incubation period between the supply of the indium source and the nucleation, the latter data being obtained by means of in situ surface reflectivity measurement. XPS analyses confirmed that the TBP and tertiarybutylarsine (TBAs) pre-flow introduced, respectively, P and As on the Si surfaces resulting in a change in surface energy. The surface with As exhibited a larger surface energy and shorter incubation period, which are preferable for better nucleation. The coverage of As on the surface, however, appeared less reliable than that of P, i.e., pre-flow with TBP was superior to pre-flow with TBAs in terms of uniformity of surface coverage. This finding is useful for achieving high-yield nucleation in small growth openings in MC-SAG. [Copyright &y& Elsevier]

Abstract: To investigate mask effects on InGaN selective area metal-organic vapor-phase epitaxy (SA-MOVPE), in-plane thickness profiles of InGaN were investigated with various indium contents covering between InN and GaN. A numerical simulation employing vapor-phase diffusion (VPD) model was also carried out for the quantitative analysis of VPD effect. At the growth temperatures of 650 and 700°C, the indium content in the vapor phase and that in the solid phase exhibited almost linear relationship, suggesting that the growth of InGaN can be approximated as the superposition of the growth of InN and GaN. The effective vapor-phase diffusion length D/k s of GaN was much smaller than InN. The profile of the InGaN growth rate in the selective area became more gradual as the solid indium content increased, and the trend seems to be the linear interpolation between the profiles of GaN and InN. However, as the indium content increases, deposition selectivity between mask and crystal surface become degenerated, and the VPD effect was almost canceled when the solid indium content exceeds 0.5. Although further improvement on the growth conditions is necessary to improve selectivity, basic information for the design of the SA-MOVPE of InGaN has been obtained, which will contribute to InGaN-based monolithically integrated multi-wavelength devices. [Copyright &y& Elsevier]

Abstract: The pulse injection (PI) growth method in which trimethylaluminium (TMAl) and NH3 are alternately supplied was used to grow AlN layer at 800°C. It was found that the process parameters in the PI method such as TMAl supply time (τ TMAl), TMAl partial pressure (P TMAl), and 1st H2 purge time (τ H1) had great influence on the crystal quality and surface morphology. Control of the growth rate to 1 monolayer (ML)/cycle resulted in highly improved crystal quality. 3.91×10−4 mbar of P TMAl and 1s of τ H1 were also found to be very effective in realizing high crystal quality showing narrow (0002) and (101¯2) full-width at half-maximum (FWHM) values confirmed by high-resolution X-ray diffraction (HRXRD) rocking curve measurement. This is because the agglomeration of initial AlN islands and adducts formation by the gas-phase reaction could be suppressed under these conditions. According to the second ion mass spectroscopy (SIMS) measurement for the AlN layer grown by PI method (PI-AlN), the impurities concentrations of hydrogen, carbon, and oxygen showed several times lower levels than those of AlN layer grown by the conventional continuous method (C-AlN) at same 800°C. Moreover, the impurities concentrations in PI-AlN layer were almost same with those of C-AlN grown at 1240°C. It clearly shows the effectiveness of PI method in enhancing reduction reaction by NH3. [Copyright &y& Elsevier]

Abstract: In situ passivation of GaAs surface subsequent to the growth in a metalorganic vapor phase epitaxy (MOVPE) reactor has been made possible using trimethylaluminum (TMAl). The adsorption layer on GaAs, presumably consisting of aluminum and the decomposition product of TMAl, was oxidized upon exposure to air to form thin AlO x layer. TMAl supply of only 0.5 monolayer completely prevented the oxidation of As on the surface, as confirmed by XPS. The passivation layer mostly prevented the oxidation of As upon O2 annealing for 5min at 250°C. For the successful passivation, complete desorption of excess As on the GaAs surface was essential prior to the injection of TMAl. Otherwise, AlAs layer was formed and arsenic oxide was inevitably formed. The optimum length of H2 purge to desorb As was determined to be 2min with in situ surface monitoring using reflectance anisotropy spectroscopy (RAS). This passivation method, combined with the succeeding deposition of Al2O3 as a gate dielectric in a different reactor, provides the GaAs/gate interface without As-oxide. The method is applicable to the MOVPE growth of electron channel layers containing As for III–V metal–insulator–semiconductor field effect transistors (MISFETs). [Copyright &y& Elsevier]

Abstract: We investigated the dependence of the growth mode on the Ga content in micro-channel selective-area MOVPE of InGaAs on Si(111) substrates by changing the partial pressure of a Ga source. The Ga content in the crystal was affected by the initial nucleation and the shape of InGaAs islands after growth. In the growth of InAs, a single columnar nucleus was generated in each open window and a hexagonal column was eventually grown. The content of the initial nuclei of InGaAs were close to InAs. As the partial pressure of a Ga source was increased, the number of nuclei in a growth area increased, their shape became rounded, and a slight amount of Ga was incorporated into the nuclei. The InGaAs islands showed enhanced lateral growth as the partial pressure of a Ga source was increased and incoherent growth without specific crystallographic planes became apparent at a high Ga content. The InGaAs islands that grew in the lateral direction had an inhomogeneous Ga content with a higher Ga content at the peripheral region. It appears that incorporation of Ga suppresses coherent growth of In(Ga)As in the vertical direction and enhances lateral growth, although high Ga content can induce incoherent growth. [Copyright &y& Elsevier]

Abstract: Two-dimensional numerical simulation on growth rate non-uniformity of selective area growth (SAG) in metal-organic vapor phase epitaxy (MOVPE) is an effective method to examine the surface reaction kinetics, which is difficult to be investigated in mass-transport limited growth regime. Non-linear kinetic analysis based on the Langmuir–Hinshelwood mechanism is revealing the intrinsic process in MOVPE. Two important kinetic parameters, surface reaction rate constant (k s n) and adsorption equilibrium coefficient (K), were successfully extracted from GaAs SAG–MOVPE on (100) exact and 2° off misoriented substrates in the temperature range of 520–600°C. The activation energy is 126–127kJ/mol for k s n, and −53 to −59kJ/mol for K. The surface coverage of Ga-species during the GaAs growth can be estimated from these kinetic parameters as 0.05–0.60. There is a critical temperature (T c) for the conversion of GaAs surface reaction mode. When growth temperature is higher than T c, non-linear kinetic can be simplified as linear kinetic mode which is easier in calculation. T c was found to be 600°C for (100) exact GaAs substrate and 650°C for 2° off substrate. [Copyright &y& Elsevier]

Abstract: Selective area metalorganic chemical vapor deposition (SA-MOCVD) is effective for the monolithic integration of semiconductor optical devices. Using appropriate patterns of SiO2 masks on a substrate, we can fabricate multiple quantum wells (MQWs) of In1−x Ga x As y P1−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) In1−x Ga x As y P1−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. [Copyright &y& Elsevier]

Abstract: Selective Area Metalorganic Vapor Phase Epitaxy (SA-MOVPE) growth of compound semiconductor, such as In1–x Ga x As y P1–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. [Copyright &y& Elsevier]