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A mixture of ultrafine submicrometer-sized BaCO3 powder and TiO2 (rutile) powder was calcined in air at 700°C, 800°C, and 900°C, and then quenched to liquid nitrogen temperature in each case. The cross-sectional quenched specimens were characterized by spatially resolved electron energy-loss spectroscopy (SR-EELS). The energy-loss near-edge structures (ELNES) were sequentially extracted at 1.3 to 5.3 nm in width from SR-EELS image obtained from the rectangularly cut SR-EELS slit aperture put on the synthesized BaTiO3 layer and TiO2 rutile powder. The ELNES of Ti-L2,3 edges and Ba-M4,5 edges clearly show fine structure changes from the surface of BaTiO3 layer to the TiO2 bulk region reflected from crystallinity of synthesized BaTiO3, lattice distortion of TiO2 caused by Ba diffusion, and lattice misfit between BaTiO3 and TiO2 without formation of Ba2TiO4 and other titanate phases.

A resonance-multiphoton-ionization sputtered neutral mass spectrometry (SNMS) instrument for submicron microarea analysis was developed. The laser system for producing resonance ionization in this SNMS consists of two yttrium aluminum garnet (YAG) lasers and three dye lasers. A combination of these laser beams, which makes available a maximum of four colors from the dye lasers and YAG lasers, can be simultaneously focused above a sample. The primary-ion-beam optical system, which uses a liquid-metal ion source, was developed specifically for this instrument. This system provides an ion-beam current density of more than 8A∕cm2 at a beam diameter of about 30nm. The depth profile of iron in a submicrometer microarea on a silicon wafer was obtained at a useful yield of about 5%, and the lateral profile of phosphorus in a rectangle area about 1400×500nm2 was obtained at useful yield of about 0.2%.

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The lateral profile of boron in an actual microdevice was obtained by 3D analysis—using the newly developed resonance photoionization sputtered neutral mass spectrometry (SNMS) instrument—with a detection limit of 10 18 atoms/cm 3 . The primary ion beam optical system of the instrument uses a Ga liquid metal ion source. The Ga beam diameter was about 30 nm and the ion beam current was about 60 pA. The analysis time to get the profile was about 40 min. Boron was excited by using one ultraviolet photon (249.7 nm) and by one visible photon (563 nm), and then it was ionized by an infrared photon (1064 nm): the so-called three-color resonance ionization. Lateral diffusion profile of boron in the device after chemical vapor deposition (CVD) including heating the wafer was also obtained. These results mean that this SNMS instrument will enable us to easily determine semiconductor processing conditions.

We have developed analytical instruments based on new concepts for failure analyses of devices of 100 nm dimensions or less. They are a sputtered neutral mass spectrometer with focused ion beam for highly sensitive element analysis in microarea (10 18 atoms/cm 3 in 30 nm area), transmission electron microscope (TEM) with electron energy loss spectrometer for chemical bond analysis in less than 2 nm area, Nanoprober for electrical characteristics inspection in actual circuits, computed tomography-TEM for three-dimensional observation of crystalline defect with 1 nm spatial resolution, atmospheric pressure ionization mass spectrometer for trace impurities ppq (parts per quadrillion) analysis in gases, and glow discharge optical emission spectrometer for rapid and precise composition analysis. Using these instruments, it was found that the formation of SiO 2 or TiO x film by water from titanic acid (TiO x ·H 2 O) is the cause of the high resistivity in a contact (CVD-W/CVD-TiN/Ti/Si) and vaporization of silicon dioxide by phosphorus trifluoride (PF 3 ) is the cause of voids in interlayer dielectric film borophosphosilicate glass.

The structure of Si layers deposited on a Si(001) 2×1 surface at room temperature is investigated by reflection electron microscopy. After the sample heating by direct current, the structure of the deposited layer returns to the 2×1 surface at coverages below 1 monolayer (ML), but changes to a rough surface with the 2×1 and the 1×2 domains at coverages above 1 ML. Since the vacancies exist in the deposited layer at coverages below 1 ML, these vacancies will accelerate the recovery process of the 2×1 surface by enhancing adsorbate migration.

The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices.

We investigated the effect of the strain-compensated structure of InGaAs(+)/InGaAs(-) multiple quantum wells (MQWs). Photoluminescence (PL) spectroscopy and thickness fringes by a transmission electron microscopy were used to evaluated the optical and structural crystal quality. For the +0.5/ −0.5% strain-compensated cases, lattice distortion was not observed, and PL intensity increased when the number of periods increased from 5 to 15. Crystal quality was improved by using the +0.5/ −0.5% strain-compensated MQW instead of the +0.5/0% compressively strained MQW. It was possible to increase the stack thickness of the strained MQWs. However, crystal quality was degraded with increase in strain. For the +1.25/ −1.25% cases, PL intensity decreased when the number of periods increased from 5 to 15, and defects were observed in a 15-period sample. Moreover, crystal quality was degraded by using the +1.25/ −1.25% strain-compensated MQW instead of the +1.25/0% compressively strained MQW.

We report on the crystalline improvement of InP layers grown on GaAs substrates by using sawtooth-patterned substrates. The period of sawtooth pattern was 1.2 μm and the layers were grown by low-pressure metalorganic chemical vapor deposition. Cross-sectional transmission electron microscope observation is applied to examine the effectiveness of the sawtooth-shaped hetero-interface for the reduction of threading dislocations in InP layers which accommodate lattice mismatch. A remarkable decrease in the full width at half-maximum values of the X-ray diffraction peaks was obtained, signifying a dramatic crystalline improvement due to the reduction of dislocations by the sawtooth-shaped interface. The unevenness of the layer surface which originates from the sawtooth shape of the substrate can be readily smoothed by thermal cycle annealing, which is accompanied by additional crystalline improvement. Moreover, an attempt to put a thin strained interlayer in the epitaxial layer as a defect filtering tool is also presented.

有機金属の熱分解を利用した気相化学成長法 (MOCVD 法) により, GaAs および InAs ホイスカーのエピタキシャル成長を検討した。成長温度400～500℃ の範囲を中心にホイスカーの太さ, 長さ, および成長方向に関する条件を調べた。ホイスカーは太さ 20～200nm, 長さ 100～5000nm の範囲でほぼ寸法制御でき, また, 成長方向は基板の結晶面方位により正確に制御できることがわかった。ホイスカーの成長は, 気相―液相―固相共存成長機構により説明できる。透過電子顕微鏡による結晶構造解析により, ホイスカーには, 閃亜鉛鉱型とウルツ鉱型との2種類の構造が現れることがわかった。フォトルミネッセンスにより, GaAs ホイスカー中のキャリヤの量子閉じ込め効果, また, イオウ処理による表面状態の変化を調べた。

We have improved both the spatial resolution and precision of three-dimensional (3D) electron microscopy, which is based on conventional scanning transmission electron microscopy (STEM), by using a micro-pillar specimen together with a 3D analysis holder, and by introducing marker-assisted image alignment prior to 3D reconstruction. Our 3D STEM measurement of aggressively scaled metal-oxide-semiconductor (MOS) gate structures not only successfully showed the z-axis positional dependence of gate-edge profiles and edge-roughness profiles such as line edge roughness (LER) and line width roughness (LWR), but also revealed uniformity of each layer of which the gate structure was composed. Such observations are very important in controlling future device characteristics, but are difficult to obtain using other measurement techniques.

Ultrathin GaAs wires as thin as 15–40 nm and about 2 μm long have been grown on a GaAs substrate by metal‐organic vapor‐phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550 °C using trimethylgallium and arsine (AsH3) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling‐bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc‐blende type for the growth temperature range of 460–500 °C, but it changes to the wurtzite type at 420 °C and temperatures higher than 500 °C. It is also found that the wires have a twin‐type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 t...

Publisher Summary This chapter describes Hitachi's efforts to develop cold-field emission (CFE) technology and scanning transmission electron microscope (STEMs). The chapter introduces cutting-edge application data obtained with the latest CFE-STEMs, highlights Hitachi's contributions to field emission (FE) technology development, and shows how the knowledge gained has been passed from generation to generation at Hitachi. The chapter also shows how CFE scanning electron microscopes (SEM)/ STEM technologies were established. The fusion of TEM technology by Hitachi started before World War II, and the CFE technology introduced by Crewe played an important role in Hitachi's development of FE-STEMs. These were not fortuities. The very strong enthusiasm of the researchers and designers at Hitachi met the challenge to develop the world's highest performance STEMs. Their enthusiasm enabled Hitachi to develop various types of STEMs, from the 50-kV STEM in 1975 to the latest HD-2700 dedicated STEM. Along the way, M. Haider and H. Rose developed Cs-correction technology and it was introduced into the HD-2700. The result was elemental and chemical-bonding–state mapping and high-resolution STEM image observation at an atomic order. These microscopes contributed to the fine structure analysis of nano-materials, nano-electronic devices, and nano-biomaterials in various fields. CFESTEMs have become an essential analytical tool in many fields.

Optical properties of quantum-size GaAs wire crystals grown by organometallic vapor-phase epitaxy (OMVPE) are measured. The typical size of the wire-shaped microcrystals is 1–5 μm long and 10–200 nm wide. Photoluminescence measurements at 4 K reveal spectral features dominated by free carrier to acceptor impurity recombination. A free exciton recombination line is also observed and is more intense relative to other features than that observed from a conventional OMVPE epitaxially grown layer. Small spectral shifts (0.5 meV) of the free exciton and the acceptor-bound exciton recombination lines are considered to be due to the effects of quantum confinement on the energy levels of the system.

Molecular beam epitaxy (MBE) of Si atoms onto a Si(001) 1×2 surface is investigated using reflection electron microscopy. A 1×2 surface with wide 1×2 and narrow 2×1 terraces is prepared by passing a direct current from the down side to the up side at the surface steps. After sample heating to 900 °C using an alternating current without deposited Si atoms, the 1×2 surface changes to a double-domain surface, where the width of the 2×1 terraces is approximately equal to that of the 1×2 terraces. With MBE, however, the 1×2 surface remains the 1×2 surface, and the double-monolayer-height islands with an approximately circular shape are stably formed on it.

A 59Co nuclear magnetic resonance measurement and a transmission electron microscope observation are utilized to investigate the compositional distribution of Co‐Cr films with and without heat treatment. The spin‐echo spectra of evaporated films are found to be entirely different from those of Co‐Cr alloy powders. The spectra of films comprise a very complicated hyperfine field distribution and the resonant frequencies are much higher than those of powder samples, implying the existence of various kinds of segregation regions typical of a film. Chrysanthemumlike patterns, which disappear with heat treatment, are also observed for chemically etched films. This disappearance is accompanied by the disappearance of the highest‐frequency resonant line.

A new scanning transmission electron microscope has been developed for three-dimensional (3D) observations of nanostructures. Using double spherical fulcra, accurate eucentric rotation was achieved. Cylindrical specimens for 3D-observation were prepared by a microsampling technique using a focused ion beam. Copper via-holes of a semiconductor memory device and ZnO particles were observed by the 3D-STEM from different directions, and 3D-data of the ZnO particles were successfully reconstructed in a topography mode.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Needle‐shaped quantum size microcrystals as thin as 10 nm have been selectively grown by employing reduced pressure organometallic vapor phase epitaxy using trimethylgallium and arsine as source materials. The microcrystals grown within a SiO2 window area have their growth axes along the [111] direction. Transmission electron diffraction analysis shows that the crystal structure of microcrystals is consistent with the zinc‐blende structure of GaAs. The mechanism for growing the needle‐shaped crystals is similar to a vapor‐liquid‐solid (VLS) equilibrium phase growth model. From photoluminescence measurements at 4.2 K, it is found that the microcrystals show a very distinct spectra for free exciton and neutral acceptor‐bound exciton recombinations, meaning good crystal quality.

A novel backside-analysis technique has been developed to identify the locations of failing transistors in manufactured LSIs. Local gate doping depletion in p+ salicide gates of PMOSFETs, which reduces drain current, was visualized for the first time. Our method consists of backside etching and subsequent selective wet etching of the gate electrode. Si substrate material was removed with a highly selective Si etchant without damaging the gate-oxide film. After the gate-oxide film removal, a locally depleted gate was selectively etched using the same etchant. Since the etching rates of nondoped Si and n+ Si are much higher than that of p+ Si for the etchant, the depleted p+ gates were well defined. Through TEM observation, we found that a large grain lay on an active channel region of a PMOSFET. This led us to attribute the gate depletion to the difference in the impurity diffusion between large and small grains. This demonstration confirmed that our technique should be quite useful for identifying failing transistor locations in manufactured memory and logic LSIs.

Composition and strain depth profiles in heterostructures such as AlGaAs/GaAs, InGaAs/InP and SiGe/Si have been analyzed with a high resolution of 0.5 nm by using the thickness fringes in a transmission electron microscope image. This diagnostic method is found to successfully evaluate the compositional disordering caused by annealing multiple quantum well structures with abrupt interfaces, and determine the difference in strain distribution in the strained-layers with various lattice mismatches. Both the composition and strain depth-profiles are analyzed quantitatively by the image simulation based on the dynamical theory of electron diffraction. This method is also useful for sensitively detecting ion-implantation-induced defects.

To clarify the origin of on-state drain current (ION) variability in metal–oxide–semiconductor field-effect transistors (MOSFETs), we applied three-dimensional scanning transmission electron microscopy (3D STEM) observation to two transistors that had different ION values but the same threshold voltage (VT). The results clearly showed a difference in the distance between the gate and source/drain silicide, suggesting that the ION difference between two transistors can be explained by the difference in the source/drain extension resistance. We showed that it is possible to discuss the 3D device structures in relation to their electrical characteristics.

We have developed a novel stand-alone diagnostic system that can analyze a semiconductor wafer surface in each process without introducing contamination. This allows us to analyze the relationship between chemical conditions and device properties.A UHV (Ultra High Vacuum) wafer transfer chamber is used between the measuring apparatus and the semiconductor processes. The chamber vacuum system, which consists of a battery driven ion pump and a liquid N2 shroud, achieves a pressure of 2 × 10−8 Pa (corresponding to about 100 min. until one monolayer of contamination has been adsorbed).Wafer transfer lines have been constructed between semiconductor vacuum processes, CVD (Chemical Vapor Deposition) and measuring instruments, ESCA (Electron Spectroscopy for Chemical Analysis) and TEM (Transmission Electron Microscope). Our results from ESCA and TEM showed measurements that carbon contamination and oxidation was suppressed.

The compositional distribution of Co-Cr vacuum evaporated films is investigated using the 59Co nuclear magnetic resonance technique. The dependence of the spin-echo spectra of Co-Cr films and powders on Cr concentration is measured. The spectra of the films evaporated at 260°C are found to be similar to those of powder samples with the Cr concentration of approximately 6 at%, although the Cr concentration of the films is between 10 at% and 24 at%. It is concluded that the Cr concentration of the ferromagnetic regions in Co-Cr films remains at 6 at%, although Cr concentration increased to 25 at%. The spin-echo spectra of the films evaporated at 160°C show that the Cr concentration in ferromagnetic regions is slightly higher than that found in the films deposited at 265 °C. This implies that segregation is less developed in the 160°C films The relationship between the magnetic properties and the segregation is also discussed

The performance of electronic devices, such as dynamic random access memories, is degraded by contamination due to impurity atoms as well as crystalline imperfections created during processing. The evaluation of those degradation causes is generally done using an analytical transmission electron microscope. The information obtained, however, is limited to two-dimensional images of the specimen as seen from a single direction. Advanced semiconductor devices with finer-pattern structures are expected to exhibit larger fluctuations in device performance due to the spatial distribution of the faults. A new method has thus been examined to determine the atomic species and to reconstruct three-dimensional (3-D) images of the specimen structure by using high-angle hollow-cone dark-field transmission electron microscopy (HADF-TEM).A incident angle controller was added to a conventional TEM to control the electron-beam deflection coils. This enables the incident electron beam to be inclined and rotated, providing hollow-cone illumination of the specimen, as shown in Fig. 1.

A highly accurate composition analysis method for (Pb,Zr)TiO3 (PZT) thin films was developed that uses a scanning electron microscope/energy dispersive X-ray spectrometer (SEM/EDX). This method, highly accurate (HA)-SEM/EDX, consists of two measurements with different electron beam acceleration voltages to control the signal generation depth. The measurement time is sufficiently elongated to reduce the statistical noise. Measurement accuracy of the PZT composition is ±1%, which is sufficient to predict the electrical characteristics of PZT capacitors. We applied HA-SEM/EDX to the failure analysis of PZT capacitors, and found that composition variation was the cause of failure in both failed samples we examined. The composition variations of PZT within a Si wafer were also measured. The composition variation of a PZT film fabricated by the sol-gel method was over ±2%, which was much larger than that of PZT deposited by ozone jet evaporation method (±1%).

The characteristics of electronic and optical devices, which have been developed utilizing a strained superlattice composed of multilayered structure accommodating lattice mismatch, are considerably affected by the strain distribution at the heterointerfaces. It has been, however, very difficult to measure the nanometer areas due to poor spatial resolution of the usual evaluation methods such as X-ray diffraction, Raman scattering, photoluminescence.The authors proposed a new transmission electron microscopy based on the compositional analysis by thickness-fringe (CAT) which was successfully applied for evaluating the compositional profiles in GaAs/AlxGa1−xxAs superstructures with a high spatial resolution of 0.4 nm. In this study, the CAT method is applied to evaluate the strain distribution with high spatial resolution and sensibility. The intensity distribution of the thickness fringe is affected not only by the composition but also by the Bragg conditions of electron diffraction. The lattice planes near the heterointerface bend due to the lattice distortion between two crystals with different lattice constant. The change of Bragg condition at the bent plane can be detected in the CAT image as the shift of thickness fringe.

Recent progress of transmission electron microscope(TEM) enables us to perform electron diffraction from nm-sized areas(nano-diffraction) with a good correspondence with HREM. Nano-diffraction is useful for obtaining local structural information. One of the present authors (NT) applied the method to interfaces of GaAs/AlGaAs superlattices for detection of compositional variation of aluminum(Al) and to nm-sized γ-iron crystallites in MgO for analysis of the strain. Although nano-diffraction has been performed successfully in STEM instruments by Cowley and others, the method in TEM has an advantage in a good compatibility with the structure-imaging method and the established bright and dark-field(BF & DF) imaging methods. In the present paper we report for the first time the detection of lattice strain around interfaces of InP/InGaP strained superlattices as well as results of GaAs/InGaAs, GaAs/AlGaAs and Ge/Si superlattices by using the TEM nano-diffraction method.The nano-diffraction was performed with 200 kV transmission electron microscopes of Cs = 1.2 mm(JEM-2000FX) and Cs = 0.5mm(JEM-2010L Before focusing an election probe, HREM and DF images of the interfaces were taken in the [100] zone axis at 100-400 k in direct magnification.

The algebraic method was applied for transmission electron microscope (TEM) images taken from four directions. The reconstruction accuracy of this method was then evaluated for a 3-dimensional specimen structure. The reconstruction error was simulated by using various images which contain projection error, dark current noise, and position error. A 10% projection error and 20-dB dark current noise in the projection image resulted in reconstruction errors of 15% and 13%, respectively. On the other hand, the position error influence was so extreme that 58% reconstruction error was induced by displacement of only ±4-pixels between the projection images. It was found that a position alignment of images within ±1 pixel was necessary in order to achieve proper reconstruction. A new position alignment method using the center of gravity of a projection image is applied for TEM images of uranyl acetate. Using this alignment method, a 3-dimensional structure was successfully reconstructed from four images.

Three-dimensional reconstruction of crystal structures by filtered convolution back projection of high-angle hollow-cone dark-field transmission electron microscope images (HADF images) of a specimen is investigated. To determine the distribution of Cu particles in Si crystal from reconstructed images, the necessary conditions are estimated. Undistorted distribution of particles is obtained from a simulated reconstruction when the specimen is inclined between ±50°, the inclination axis direction error is ±2° and Poisson noise is 30 db. Under these conditions, the distribution of Cu particles in a Si crystal is experimentally reconstructed.

Methods of determining atomic species and reconstructing three-dimensional images of the specimen structure were examined by high-angle hollow-cone dark-field transmission electron microscopy (HADF-TEM). The contrast of the HADF image systematically changed depending on the atomic number and the size of particles deposited on carbon films. The relationship between the contrast and the atomic number was well simulated using the theory of multiple electron scattering. The specimens, which were Cu particles precipitated in Si crystal, were observed with an inclination from -50 to 50° by steps of 2°. The images were processed using computed tomography. It became clear that the spatial distribution of the Cu particles differed depending on whether the precipitated position was a dislocation or a (111) stacking fault.

InGaAsP/InP multilayers were deposited on InP substrates. Multilayer internal stress was controlled by changing the GaAs concentration. The strained lattice structures in InGaAsP/InP multilayers under compresive, tensile, and mixed strain (zero-net strain) are analyzed by using the thickness fringes in bright- and dark-field transmission electron microscope images. The thickness fringe shift near the multilayer/substrate interface shows lattice plane bending in opposing directions for the 0.5% compressive and tensile strained structures. The opposing lattice bending is canceled out in the zero-net strain structure, which results in a transition from cubic to tetragonal lattice distortion in the multilayer. This distortion enlarges the critical thickness to six times that of the compressive or tensile strained structure. The zero-net structure, however, can't maintain greater than ±1.4% strain because the induced stress exceeds the limit of elastic distortion. The influence of strain in these structures, as it corresponds to photoluminescence characteristics is also analyzed.

This paper investigates the difference in crystal quality between strained-layer multiple quantum wells with compressive (+0.5%) and tensile strains (-0.5 %). For the compressive strain, the photoluminescence intensity decreased and the length of fringe bending increased from 250 Å to 500 Å when the number of periods increased from 5 to 15. The amount of fringe bending increased when the InP thickness decreased, especially when the strain was compressive. We also investigated the relaxation process in an InGaAs layer as a function of the layer thickness (from 25 nm to 2 µ m). For a compressive strain (+1.1%), misfit dislocations were observed near the interface between InGaAs and InP substrate. On the other hand, for a tensile strain (-1.1 %), we observed cracks instead of misfit dislocations. Moreover, the cracks were considered to increase the X-ray full width at half maximum of both the InGaAs lattice-mismatched layer and the InP substrate.

A specimen transfer chamber that enables a specimen to be transferred in vacuum from a thin-film growth apparatus to an ultrahigh-vacuum transmission electron microscope (UHV-TEM) was developed. This chamber was applied to observe, for the first time, the as-grown state of Fe-Mn thin films and the changes occurring during their oxidation. The oxidation process of 12-nm-thick Fe-Mn films on a carbon support film was observed by controlling the vacuum in the transfer chamber. Just after a film specimen was transferred, it had a polycrystalline single-phase structure. When the film was exposed to pressures from 3.8×10-6 Pa to 1 atm, (Fe-Mn)2O3 gradually appeared around the Fe-Mn grain boundaries. The Fe-Mn grains changed to (Fe-Mn)2O3 grains after 47 h of exposure to air.

The relationship between the microstructure and photoluminescence of porous Si is investigated. High-resolution scanning electron microscopy shows that porous Si has a small-particle structure, with particle sizes ranging from several nm to several tens of nm. Transmission electron microscopy shows that these particles are composed of single-crystal Si spheres covered with an oxide layer. Porous Si with larger particles emits light with longer wavelengths. This suggests that the effective photoluminescence of porous Si is due to three-dimensional carrier confinement in quantum boxes.

Crystal structures of GaAs and InAs whiskers grown by metalorganic vapor phase epitaxy are evaluated by means of a transmission electron microscope. The whiskers are grown epitaxially on GaAs substrates with diameters of 20-100 nm and lengths of 1-5 µm. They have the following characteristics. 1) GaAs whiskers have layered structures with 2-30 nm period, that are the 111 rotating twins of the zinc-blende type. 2) InAs whiskers also have layered structures which consist of wurtzite and zinc-blende type crystals. The wurtzite type InAs is observed for the first time in this study. The volume ratio of these two types strongly depends on the growth conditions, such as substrate temperature and material gas pressure. This suggests that defect-free whiskers with a single phase that are useful for quantum wire devices can be grown by controlling the growth conditions.

Lattice bending around the interfaces of strained InP/InGaP/InP superlattices was analyzed by using thickness fringes in the dark-field electron microscopy and nanometer-area electron diffraction patterns. The present paper is complementary to a previous paper about strain detection by using thickness fringes in the bright-field electron microscopy (Jpn. J. Appl. Phys. 30 (1991) L52). By using the two methods, lattice bending around the interfaces of the superlattices with a lattice misfit of 1% was quantitatively evaluated in a three-dimensional form. Comparison between the methods and the usual lattice-imaging method in high-resolution electron microscopy(HREM) is discussed.

Compositional analysis by the thickness-fringe (CAT) method is applied to evaluate the strain distribution at the InP/In1-x Ga x P heterointerface in the direction of epitaxial growth. It has been found that the strain due to the lattice mismatch between In1-x Ga x P and InP is clearly detectable as a bending of the equal-thickness fringe in the CAT image. The crystal planes in the strain field bend as a result of lattice distortion, causing both change in the Bragg condition of the electron diffraction and fringe bending. The fringe bending depends on the amount of lattice mismatch. The strain distribution is analyzed by comparing observed and simulated CAT images. The CAT method is also useful for evaluating the strain distribution with a high spatial resolution.

The Be transport during MBE growth of GaAs has been studied. The Be surface segregation was clearly separated from the Be diffusion by using misoriented as well as nominal (100) substrates. The Be profiles measured by SIMS showed that the surface segregation was suppressed by the substrate misorientation even when the anomalous diffusion took place. The CAT observation revealed that the Be-induced disordering of superlattices occurred for 6×1019 cm-3 doping. The width of the disordered region was found to depend on the substrate misorientation, which was due to the misorientation dependence of the surface segregation. The step exchange model has been successfully employed to account for these results.