Search

Using in situ synchrotron X-ray reciprocal space mapping, this study investigates the evolution of lattice deformations in the InGaAs/GaAs(1 1 1)A structure with or without a thin InAs layer grown by molecular beam epitaxy. During the initial growth phase, InGaAs directly grown on GaAs(1 1 1)A showed an anomalous lattice shrinkage along the c-axis, with no change in the indium composition. Conversely, the InGaAs grown on InAs/GaAs(1 1 1)A showed no initial lattice distortion, but a variable indium composition. The evolution of the diffraction peak broadening was also monitored. The results confirmed that the thin InAs layer effectively improved the crystal quality during the initial growth of InGaAs.

In this study, we analyzed the influence of indium supply on the growth dynamics of gold-catalyzed InGaAs nanowires by in situ synchrotron X-ray diffraction. A high In/Ga supply ratio results in strong size inhomogeneity of Au particles and interrupts the nanowire growth at a certain point of time. Based on the experimental results, we discussed the state of Au catalysts with high indium content during the nanowire growth. We found that a growth temperature below the eutectic temperature is essential to avoid the growth interruption and maintain the nanowire growth. The high In/Ga ratio necessitates accurate size control of Au particles before growth for further improvement of the nanowire growth.

In this work, in situ synchrotron X-ray diffraction reciprocal space mapping (RSM) measurements were carried out for the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) growth of GaInN on GaN and InN layers, which were also grown by RF-MBE on commercialized GaN/c-sapphire templates. In situ XRD RSM measurements were performed using an MBE apparatus directly coupled to an X-ray diffractometer at the beamline of the synchrotron radiation facility SPring-8. It was observed in situ that both lattice relaxation and compositional pulling occurred during the initial growth stage, reducing the strain of GaInN on GaN and InN. Different initial growth behaviors of GaInN on GaN and InN were also observed from the results of the evolution of GaInN integrated peak intensities.

In situ synchrotron X-ray reciprocal space mapping was carried out to investigate the evolution of lattice strain and crystal structure of InGaN/GaN heterostructure nanowires grown by molecular beam epitaxy. At the beginning of the growth, the InGaN lattice was compressively strained to that of GaN, resulting in the pseudomorphic growth. This strain started to relax at a thickness of 3 nm and fully relaxed at 9 nm. Concomitantly, polytypes consisting of the zinc-blende and wurtzite phases were formed in InGaN., Compound Semiconductor Week 2019

The molecular beam epitaxial (MBE) growth of twenty-period InGaN/GaN multi-quantum-well (MQW) nanowires was investigated by in situ X-ray reciprocal space mapping (in situ RSM). The evolution of strain, composition, and their inhomogeneities during the growth significantly varied with increasing number of QWs. After the growth of the ninth QWs, InGaN was tensilely strained with poor crystalline quality as inferred from the diffraction peak position and shape. At the same time, another peak emerged at the higher indium composition, suggesting the segregation of InN in the MQW nanowires., Compound Semiconductor Week 2019

In-situ X-ray diffraction was used to investigate initial stages of GaN growth on graphene-covered SiO2 substrates with or without AlN buffer layers by plasma-assisted molecular beam epitaxy. The in-plane lattice parameter of GaN remained almost constant during growth without AlN buffer layers, confirming weak interactions between GaN and graphene. On the substrate with AlN buffer layers, the GaN lattice parameter continuously changed from AlN value to GaN value, indicating that the AlN islands act as seeds for GaN growth. Besides, GaN has preferential orientations epitaxial to graphene. Graphene can be used as a template of GaN growth on amorphous substrates.

In situ three-dimensional X-ray reciprocal space mapping ( in situ 3D-RSM) was employed for studying molecular beam epitaxial (MBE) growth of InGaAs multilayer structures on GaAs(0 0 1). Measuring the symmetric 004 diffraction allowed us to separately obtain film properties of individual layers and to track the real-time evolution of both residual strain and lattice tilting. In two-layer growth of InGaAs, significant plastic relaxation was observed during the upper layer growth, and its critical thickness was experimentally determined. At the same thickness, it was found that the direction of lattice tilting drastically changed. We discuss these features based on the Dunstan model and confirm that strain relaxation in the multilayer structure is induced by two kinds of dislocation motion (dislocation multiplication and the generation of dislocation half-loops).

Defect characterization in molecular beam epitaxial (MBE) compositionally-graded InxGa1-xAs layers on GaAs substrates consisting different thickness of overshooting (OS) layers was carried out using cathodoluminescence (CL) and transmission electron microscopy (TEM). We found that the thickness of the OS layer influences not only stress but also lattice defects generated in a top InGaAs layer. While the top InGaAs layer with a thin OS layer is under compression and has mainly threading dislocations, the top layer with a thick OS layer is under tension and exhibits inhomogeneous strain associating with phase separation. We will discuss the mechanisms of defect generation and their in-plane distribution based on strain relaxation at the top and OS layers. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In situ synchrotron X-ray diffraction studies during the growth of arsenide and nitride semiconductors are presented. The large penetration depth of X-rays was exploited for revealing structural changes at buried interfaces as well as near the surface. Experiments were performed at a synchrotron beamline, BL11XU, SPring-8, using a molecular-beam epitaxy chamber integrated with a high-precision X-ray diffractometer. A high-speed X-ray reciprocal space mapping technique was applied to a variety of heteroepitaxial systems including InGaAs on GaAs(001), InGaAs on GaAs(111)A and GaN on SiC(0001). Results showed that even layers as thick as 200 nm were not necessarily stable even after being buried under an overlayer but could undergo significant structural changes during growth.

This paper describes the development of a high-speed three-dimensional reciprocal-space mapping method designed for the real-time monitoring of the strain relaxation process during the growth of heterostructure semiconductors. Each three-dimensional map is obtained by combining a set of consecutive images, which are captured during the continuous rotation of the sample, and calculating the reciprocal-space coordinates from the detector coordinate system. To demonstrate the feasibility of this rapid mapping technique, the 022 asymmetric diffraction of an InGaAs/GaAs(001) thin film grown by molecular beam epitaxy was measured and the procedure for data calibration was examined. Subsequently, the proposed method was applied to real-time monitoring of the strain relaxation process during the growth of a thin-film heterostructure consisting of In0.07Ga0.93As and In0.18Ga0.82As layers consecutively deposited on GaAs(001). The time resolution of the measurement was 10 s. It was revealed that additional relaxation of the first In0.07Ga0.93As layer was induced by the growth of the second In0.18Ga0.82As layer within a short period of time corresponding to the deposition of only two monolayers of InGaAs.

Surface structures of GaAs(0 0 1) under molecular beam epitaxy conditions are described on the basis of in situ X-ray diffraction measurements. Exploiting the high-intensity, high angular resolution and element sensitivity of synchrotron X-rays, we revealed the details of the most frequently used surfaces including several phases of ( 2 × 4 ) and c ( 4 × 4 ) .

The surface structure of GaAs(0 0 1)-c(4 × 4) was investigated by synchrotron surface X-ray diffraction which is sensitive to both in-plane and out-of-plane structures. The atomic coordinates and Debye–Waller factors for up to the sixth layer from the surface are given. The resultant atomic coordinates were compared with those given by a first-principles calculation. Among a variety of heterodimer models that were examined by theoretical calculation, our data fit best a three-heterodimer model where three Ga–As heterodimers are present in one unit cell. The preference for the formation of heterodimers is discussed in relationship to the transition process from the 2 × 4 to the c(4 × 4) structures.

Molecular-beam epitaxial growth of InAs/GaAs(0 0 1) quantum dots was investigated by grazing-incidence X-ray diffraction using a diffractometer directly coupled to an molecular-beam epitaxy (MBE) apparatus. The use of synchrotron radiation and a two-dimensional X-ray detector enabled reciprocal space mapping at a rate of 9.6 s per frame. The X-ray diffraction images revealed that the strain and shape of the quantum dots change significantly during the sequential growth process consisting of island formation, growth interruption and GaAs encapsulation.

The GaAs(0 0 1)-( 2 × 4 ) reconstructed surface was investigated by in situ surface X-ray diffraction. X-ray diffraction patterns were measured with increasing substrate temperature within the β phase of GaAs(0 0 1)-( 2 × 4 ) in a constant As flux of 5 × 1 0 − 7 Torr. At relatively low temperatures up to 545 ∘C, the observed X-ray diffraction patterns agree well with the β 2( 2 × 4 ) surface. However, a different X-ray diffraction pattern was obtained at temperatures close to the α phase, while the 2 × 4 periodicity still persisted. This change is explained by partial As-dimer desorption which results in a mixture of the β 2( 2 × 4 ) and α 2( 2 × 4 ) structures.

The dynamics of the molecular-beam-epitaxy (MBE) of GaAs (0 0 1) was investigated with a surface X-ray diffractometer coupled to an MBE chamber. The diffracted intensity of X-rays was measured in real time during growth. The temporal oscillation of the intensity for the growth at 550°C was explained well by the distributed-growth model, while the intensity for the growth at 435°C showed a complicated behavior arising from the changes in the surface reconstruction and the morphology. A method for separating the dynamics of the morphology from that of the reconstruction is presented.

An X-ray diffractometer connected with a molecular-beam epitaxy (MBE) system has been constructed for in situ studies on the growing surfaces of III–V compound semiconductors. This diffractometer is based on the (4+2) type, which has four axes for orienting the sample and two axes for positioning the detector. In addition, it is equipped with an axis for rotating the receiving slit about the normal of the slit plane to align the resolution of the receiving slit properly for the surface X-ray diffraction measurement. For the alignment of the sample and the entire setup with respect to the X-ray beam, an XYZ-stage and an adjustable base plate are available. X-rays enter and leave the chamber through two Be windows welded directly to the MBE chamber. A graphite sheet which can be heated up to 250°C is placed along the inside of the Be windows to protect the Be windows from being coated with evaporated materials. Preliminary data are presented to demonstrate the feasibility of static and dynamic measurements of growing surfaces using this instrument.

JAERI Group has constructed three beamlines for carrying out their own research at SPring-8. One of the three is the bending magnet Beamline for the purpose of materials research. We will describe here the feature of the beam line and the spectrometer, and also some data which have been recently taken at this beamline.

The growth of five layers of InAs quantum dots embedded in GaAs matrices was investigated by in situ synchrotron X-ray diffraction. Time-resolved X-ray diffraction revealed the evolution of the strains and height of quantum dots during the entire growth process including the nucleation of islands and encapsulation with GaAs at various substrate temperatures. Comparisons of in situ X-ray results with postgrowth photoluminescence spectra showed a clear correlation between the structural and optical properties.

In situ X-ray reciprocal space mapping during InxGa1−xAs/GaAs(001) MBE growth is performed to investigate effects of substrate misorientations on crystallographic tilting. It was found that evolution of the crystallographic tilt for the InGaAs films is strongly dependent on both layer structures and substrate misorientations. We discuss these observations in terms of an asymmetric distribution of dislocations.

We have investigated the growth by molecular beam epitaxy (MBE) of GaAs on MnSb. MnSb epilayers on GaAs(111), GaAs(001) and In0.5Ga0.5As(111) of thickness ∼ 50 nm were used as substrates for GaAs films. The MBE growth of GaAs was monitored in situ using synchrotron X-ray diffraction and reflection high energy electron diffraction. We show data on strain relaxation and growth mode, and discuss the epitaxial relationship between GaAs(001) and MnSb(11‾01). Schematic of the molecular beam epitaxy/X-ray diffraction in situ experiment and typical 2D detector data, with GaAs(111) and MnSb(0001) diffraction features.

A molecular beam epitaxy (MBE) chamber dedicated to nitride growth was developed at the synchrotron radiation facility SPring-8. This chamber has two beryllium windows for incident and outgoing X-rays, and is directly connected to an X-ray diffractometer, enabling in situ synchrotron X-ray measurements during the nitride growth. Experimental results on initial growth dynamics in GaN/SiC, AlN/SiC, and InN/GaN heteroepitaxy were presented. We achieved high-speed and high-sensitivity reciprocal space mapping with a thickness resolution of atomic-layer scale. This in situ measurement using the high-brilliance synchrotron light source will be useful for evaluating structural variations in the initial growth stage of nitride semiconductors.

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.

Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

A new surface X-ray diffractometer based on a κ-type diffractometer will be installed in BL14B1, SPring-8. This diffractometer has an additional axis on its detector arm for rotating the receiving slit about the normal of the slit plane, in addition to two axes for positioning the detector. This additional axis is founded on the consideration of the correction factor which has been derived so as to be valid for the z-axis mode measurement using any incoming and outgoing angles of the X-ray beam. The rotational slit allows accurate measurement of the surface structure factor up to large perpendicular momentum transfer.

In situ structure analysis of GaAs(001)-c(4 x 4) has been carried out by synchrotron surface x-ray diffraction, which is sensitive to the three-dimensional structure and the atomic species. On the basis of 98 independent in-plane diffractions and 11 fractional-order rod profiles, the atomic coordinates and thermal vibration parameters were determined. X-ray diffraction results show the buckling of surface dimers and a strain field extending up to the sixth layer from the surface. An anomalous diffraction technique has been employed to specify the atomic species of the surface dimers. It has provided direct evidence of the formation of Ga-As heterodimers.

Summary form only given. Reflection high energy electron diffraction (RHEED) oscillation has been widely adopted for studies on growth kinetics and dynamics in molecular beam epitaxy (MBE). Recent developments in brilliant X-ray sources has enabled similar experiments with X-rays, which has great advantage in a straightforward interpretation of results and in a high angular resolution. In general, the diffracted intensity from surface is proportional to the surface structure factor associated with the surface reconstruction, F, multiplied by a damping factor associated with the surface roughness, m. We show that the two factors, F and m, can be obtained separately by measuring diffuse scattering around the two-dimensional Bragg peak during growth. The experiments were performed with a six-axis surface diffractometer coupled to an MBE chamber at the synchrotron radiation facility, SPring-8. This apparatus allows the sample to be subjected to X-ray measurements at the same position as prepared. The diffracted intensity of X-rays was measured during the homoepitaxial growth of GaAs[001] at a substrate temperature of 700 K. Under the condition used, the RHEED pattern changed from the c(4x4) to the 2x1 symmetry on starting the growth.

A ternary Fresnel zone plate (FZP) has been fabricated and installed at the beamline 11XU of SPring-8, in the aim of in situ studies on the growth of semiconductor nanostructures. The FZP is designed for an X-ray energy of 9.5 keV for the first-order diffraction, which is isolated by an order sorting aperture (OSA) inserted 450 mm after the FZP. The focal length of this FZP is 650 mm. The full width at half maximum of the focused beam profile was estimated to be 1.17 μm (H) × 1.38 μm (V) by the dark-field knife-edge scan. Using this FZP, micro-beam diffraction of an as-grown single InAs NW was carried out to show the feasibility of in situ study during growth.

Self-assembly of high-density InAs quantum dots (QDs) on Sb-irradiated GaAs buffer layers was observed in-situ by a time-resolved X-ray diffraction (XRD) technique using a combination of XRD and molecular beam epitaxy. Evolution of dot height and lattice constant was analyzed during InAs QD growth and subsequent growth interruption (GI), and as a result, dislocated giant dots due to coalescence and coherent dots were separately evaluated. An Sb-irradiated GI (Sb-GI) method to be applied after InAs growth was attempted for the suppression of coalescence. Using this method, the XRD intensity of giant dots decreased, and the photoluminescence intensity of InAs QDs was enhanced. High-density InAs QDs without giant dots were produced by using the combination of the QD growth on the Sb-irradiated GaAs buffer layers and the Sb-GI.

In situ real-time X-ray diffraction measurements during In0.12Ga0.88As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced.

The molecular beam epitaxial (MBE) growth and postgrowth annealing of InAs/GaAs(001) quantum dots were investigated by grazing-incidence X-ray diffraction using a diffractometer integrated with an MBE apparatus. The use of synchrotron radiation and a two-dimensional X-ray detector enabled X-ray diffraction measurements on the internal strains and height of dots at a rate of less than 10 s per frame. Mass transport by surface diffusion was found to play a major role in the nucleation of three-dimensional islands of InAs/GaAs(001).

A monitoring technique for molecular beam epitaxial growth of InAs∕GaAs(001) nanoislands is presented. With the help of synchrotron radiation, x-ray diffraction intensity mapping in reciprocal space has been measured during growth. The internal strain distribution and height of the Stranski-Krastanov islands were monitored at a temporal resolution of 9.6s. The relaxation process of internal strain inside the Stranski-Krastanov islands displayed significant dependence on the growth temperature.

The angular dependence of Kossel lines from Ge single crystals excited by monochromatized synchrotron radiation was measured precisely in the double-crystal arrangement where the first crystal acts as a sample and the second as an analyzer. The Kossel line profiles showed surface sensitivifies when the excitation beam was incident on the crystal surface at a small angle or when its wavelength was slightly shorter than the absorption edge of Ge. The profiles were compared with the calculations based on the dynamical theory using the reciprocity theorem. The relationship with the X-ray standing wave method was clarified.