X-ray Lang Topography Research Articles

Study of X-ray topography using the super-Borrmann effect.

X-ray topography exerting the super-Borrmann effect has been performed using synchrotron radiation to display dislocation images with a high-speed and high-resolution CMOS camera. Forward-transmitted X-rays are positively employed instead of reflected X-rays to reveal dislocations in relatively thick crystals by simultaneously exciting a pair of adjacent {111} planes owing to the super-Borrmann effect. Before the experiment, minimum values of the attenuation coefficients AminP for σ and π polarizations of the incident X-rays in the three-beam case are calculated. Results demonstrate that AminP for both polarizations are almost 20 times larger than those in the two-beam (usual Borrmann effect) case. The transmitted X-rays can be used to confirm the efficacy of taking topographs under the super-Borrmann conditions, as well as under multiple-diffraction conditions. Furthermore, super-Borrmann topographs can be considered for relatively thick crystals, where a conventional Lang X-ray topography technique is difficult to apply.

Структурное совершенство и состав легированных галлием термомиграционных слоев кремния

We suggest a technique of fabrication of thick heavily Ga doped by thermomigration layers of Si for modern power electronics devices. Structure perfection and layers composition as a function of formation temperature were studied by techniques of X-ray Lang topography, X-ray rocking curves and secondary ion mass spectrometry. The fabricated layers are single crystalline, no mismatch dislocations were found on the interface with the Si substrate. The Ga concentration in the layers can be varied in the range (1.6-4.8)1019 cm-3, being higher than for Si doping with aluminum.

Effect of phosphorous implantation on threading dislocation motions in SiGe/Si heterostructures

The velocity and activation energy of dislocation motions in phosphorous (P)-implanted silicon-germanium (SiGe)/silicon (Si) heterostructures with a Ge content of 3% were determined by using an etching method and the x-ray Lang topography technique. The obtained results were compared with those of the original samples. P was implanted with an energy of 100 keV and dose of 5×1012 cm–2. This implantation energy produced a peak concentration of P in the SiGe layer; at the same time, the low dose did not produce any observable defects in the SiGe layer. The temperature dependencies of dislocation velocities in the P-implanted samples were represented on an Arrhenius plot; the plot revealed that there was a decrease in the velocities and an increase in the activation energies of the dislocation motions in the P-implanted samples as compared to those of the original samples. The recovery of the dislocation velocity relative to that of the original samples was studied using various implantation species (P, nitrogen, and oxygen); it was found that the recovery began at temperatures of around 700 °C, irrespective of the nature of the implanted impurities. This indicates that certain types of defects, but not impurities, generated during the implantation influenced the dislocation motion. It is proposed that the reduction in the velocities and the increase in the activation energies of the dislocation motions are attributable to the generation of microdefects, which offer resistance to the gliding motion of a threading dislocation.

Characterization of synthesized and treated gem diamonds

Synthesized diamonds have been widely employed as polishing media for precise machining and noble substrates for microelectronics. The recent development of the split sphere press has led to the commercial HPHT (high pressure high temperature) synthesis of bulk gem diamonds from graphite and to the enhancement of low quality natural diamonds. Synthesized and treated diamonds are sometimes traded deceptively as high quality natural diamonds because it is hard to distinguish among these diamonds with conventional gemological characterization methods. Therefore, we need to develop a new identification method that is non-destructive, fast, and inexpensive. We proposed using new methods of UV fluorescence and X-ray Lang topography for checking the local HPHT stress field as well as using a vibrating sample magnetometer for checking ferromagnetic residue in synthesized diamonds to distinguish these diamonds from natural ones. We observe unique differences in the local stress field images in synthesized and treated diamonds using Lang topography and UV fluorescence characterization. Our result implies that our proposed methods may be appropriate for identification of the synthesized and treated diamonds.

Plastic deformation of copper single crystals by simulation using X-ray Lang method and molecular dynamics

Copper rectangular parallelepiped single crystals with a notch have been extended or compressed. In a crystal with a notch, partial dislocations were created near the tip of the notch in elongation as we expected. It is hard to see where the dislocations were created just looking the displaced positions of atoms, but by a simulation of X-ray Lang topography, the creation of dislocations was easily observed. Before creation of dislocations, some indication was quite clearly shown. For compression dislocations did not start near the tip of the notch but started uniformly on the surface, the effect of notch was minor.

Ultrahigh-purity aluminum single crystals with a low dislocation density grown by strain-annealing method

Aluminum single crystals with a low dislocation density were grown by the strain-annealing method from ultrahigh-purity (UHP) materials. The crystals were annealed cyclically six times to decrease the dislocation density. The number density and the Burgers vector of the residual dislocations were examined by the X-ray Lang topography and the synchrotron radiation topography with white beam X-ray, respectively. The number density and the nature of the dislocations were 1×10 3 cm −2 and 60° dislocations, respectively. These results were similar to those in the high-purity aluminum crystals. The cause of the results is attributed to the amount of residual vacancies after growth. The calculated residual vacancy concentration in crystal after slow cooling attains 1.2×10 −6, which is about ten times as large as the impurity concentration in UHP aluminum. So the residual vacancy concentration in the UHP aluminum hardly depends on the impurity concentration. It seems that the formation mechanism of dislocations by excess vacancies in UHP aluminum is similar to that in high-purity material because the amount of residual vacancies in both the crystals are nearly equivalent.

On the Microstructure of as-Grown TiN Whisker-Like Crystals

The microstructure of as-grown TiN whisker-like crystals was examined using Lang X-ray topography, transmission electron microscopy (TEM) and also the Eshelby measurement of the twist of the crystal lattice. It was found that the as-grown TiN whisker-like crystals exhibit a very high degree of structural perfection. In a few cases the observed dislocations were deformation-type dislocations and occurred only in areas of brittle fracture of whiskers. In none of the tested as-grown whisker-like crystals axial dislocations were detected.

X-ray Topographic Characterization of L-Arginine Phosphate Monohydrate Crystals

L-arginine phosphate monohydrate (LAP) organic crystals were investigated by X-ray Lang topography. Selected topographs of nearly perfect seeded grown and self-nucleated crystals show that typical defects inside are grown-in and post-growth dislocations, growth sector boundaries, and microbes, while their features are presented and discussed. No structural defects associated to the presence of step bunching on the (100) surface of the crystal have been observed by X-ray topography.

Single crystal growth of Si1 − xGex by the Czochralski technique

(111)- and (100)-Si1 − xGex single crystals (0 < x < 0.1) with diameters of up to 48 mm were grown by Czochralski technique using a crystal puller with resistance heating. An automated control system based on crystal weighing has been developed. Software provides feedback control as well as the program changes of some process parameters to optimize crystal growth conditions. Ge distribution and crystal quality were investigated by infrared transmission measurements at the absorption edge and X-ray Lang topography, respectively.

Structural analysis of 4H-SiC layers grown on 6H-SiC and 15R-SiC substrates

Structural variations and defects in both transformed and epitaxial 4H-SiC layers deposited on 6H-SiC and 15R-SiC Lely wafers have been investigated by X-ray differential diffractometry and Lang X-ray topography methods. It has been shown that the layers consist of several sublayers. These sublayers are differentiated by the amount to which they relax the interface elastic strains. In this paper these differences are shown and the character of dislocation ensembles is discussed in the context of lattice mismatch and growth conditions.

Study of crystal defects in natural diamond

To study the crystal defects in diamonds, a specimen of natural diamond crystals selected from northeast China was tested by means of Lang X-ray topography and double-crystal X-ray topography. As a result, several types of crystal defect, such as twin boundaries, dislocations, growth bands and substructures existing in the specimen were found. The morphologies of the twin boundaries have been analysed and a detailed discussion of the determination of its characteristic vectors is given. The distribution characteristics of the various crystal defects as well as their relation to the twin boundaries are presented.

Attempt to correlate threshold voltage scattering with x-ray Lang topographs for semi-insulating GaAs substrates

Because the yields of GaAs metal-semiconductor field-effect transistor (MESFET) devices are negatively impacted if ranges of threshold voltages (Vth) occur for sets of devices fabricated over the total area of the substrate, it is desirable to pinpoint the physical origin of this problem before a solution may be implemented. The presence of high dislocation densities encountered in wafers produced from liquid-encapsulated Czochralski-grown boules of GaAs may be responsible for the phenomenon of wide distributions of Vth, although this view is presently controversial. Accordingly, we have implanted silicon as a dopant into commercially supplied semi-insulating GaAs wafers, formed arrays of MESFETs, and attempted to correlate the dislocation densities determined by Lang x-ray topography with the magnitude of the scattering of Vth, including the observation of spikes, across the wafers in the 〈110〉 direction. The present results indicate that there is no clear correlation between either the magnitudes or the spatial distributions of the threshold voltages and the presence of high densities of dislocations. An alternative explanation is presented based on the presence of point defects such as interstitial arsenic in the samples.

Large-area X-ray and CL study of SI GaAs wafers from various suppliers

Homogeneity of electrical and structural properties of SI GaAs wafers is very important for implantation technology. Reflection Lang X-ray topography and integral cathodoluminescence have been used to characterize the inhomogeneities of wafers from various suppliers. Scratches, slip dislocations, cellular structure, and lineages have been observed with significant differences in distribution, density, species, and shape of the extended defects not only from supplier to supplier but also when comparing seed and tang ends of the same crystal. Direct correlation between Lang XRT and CL has been found for scratches, lineages and cell walls, but not for slip dislocations. Complex dark/white contrast of various features in CL images has been described. Besides white contrast at the cell walls, white islands inside the cells have been observed as well. The observations have been interpreted on the basis of the concept of cellular structure and slip dislocations formation and on the basis of point defect oversaturation and nucleation of As-rich precipitates capable of gettering.

Doping effect on the crystalline quality of ADP doped with chromium: I. Comparison of solution-grown and gel-grown crystals

ADP crystals doped with chromium were obtained by temperature decrease of a saturated aqueous solution either stirred (solution-growth) or gelled (gel-growth). Characterization of the doping effect was made by atomic absorption, optical observations (tapering angle, colour) and X-ray Lang topography. The global incorporation of chromium is found to be higher in the gel-grown crystals; however, the lattice strains associated with the relative segregation of chromium in the prismatic and pyramidal sectors are reduced.

On the origin of the formation of facets and deep etch pits on HCl etched {111} silicon wafers

Facet formation and the development of deep etch pits, on {111} faces of silicon which have a small misorientation to real {111}, have extensively been studied by means of phase contrast, differential interference contrast microscopy, multiple beam interferometry and X-ray Lang topography. It could be shown that the formation of shallow and deep etch pits is correlated to the presence of microdefects and dislocations. Microdefects in the form of small dislocation loops exclusively will give facet formation at medium HCl partial pressure, whereas real dislocations, which at small P HCl also lead to facet formation, at higher P HCl develop deep etch pits, because the dislocation cores open up upon further etching. A model is presented in which the formation process of shallow and deep etch pits is described by the stability of hollow cores together with the kinetic behavior of spirals.

Determination of the sign of the burgers vector for nearly screw dislocations a direct application of x-ray dynamical theory

Abstract Nearly screw dislocations perpendicular to the crystal surfaces of KDP have been studied by the Lang X-ray topography technique in the case of reflections where the bulk strain tensor gives no contrast. Stress-relaxation deformations at the intersections with the crystal surfaces give images which have been studied in both reflected and refracted beams on section topography. The interpretation of the contrast is based on dynamical theory for slightly distorted crystals and leads to the determination of the sign of the Burgers vector. The formulation adopted here (after Malgrange 1975) leads to a convenient interpretation (both qualitative and semi-quantitative) of the contrast. In particular, the interpretation of the shape and size of the stress-relaxation-deformation images is a good example of what can be done on the basis of results of dynamical theory and without any computer calculation.

Dislocations et croissance des cristaux d'aluminium par recristallisation secondaire

Dislocations of aluminium crystals grown under high vacuum ( P ⩽ 10 -8 torr) by secondary recrystallization at the expense of primary recrystallization cubic texture grains were investigated by X-ray Lang topography. We could see that quasi-linear dislocations, with Burgers vectors making an angle of 60° with dislocation lines arise from segmented helical-type dislocations present in these crystals. The origin of the latter type dislocations is ascribed to the climbing of screw dislocations under the small supersaturation of vacancies which form in the crystals during cooling. A generation mechanism of screw or quasi-screw dislocations associated with the boundary migration of secondary crystals (38° (22°) 〈111〉 Kronberg-Wilson boundary) is also described.

X-ray topographic studies of as-grown defects in natural muscovite

Two natural muscovite crystals from Governador Valadares, Brasil, have been studied by means of the Lang's X-ray topography method. Dislocation bundles lying in (001) planes as well as growth bands have been observed, which are directly correlated to the growth of {110}, {010} and { 3 1 l} sectors of the crystals. Growth dislocation Burgers vectors 1 2 [110] and 1 2 [ 110] as well as fault vectors connected with growth bands have been determined using extinction rules. In the light of defect configurations in these crystals, the “growth history” of the mica specimens has been analysed.

Observation de dislocations hélicoïdales segmentées dans l'aluminium recristallisé

Segmented helical dislocations, clearly distinguishable by Lang X-ray topography (about 1 mm long and with pitches and diameters near 0.1 mm), are found in aluminum single crystals grown by secondary recrystallization under high vacuum (P≤10−8 torr). They are characterized by repetitive sequences of three distinct Bi segments which are not quite linear and are distributed in the order ... B1, B2, B3, B2, B1, ... .

The brittle-to-ductile transition in pre-cleaved silicon single crystals

Abstract A series of fracture experiments were carried out at various strain-rates on pre-cracked silicon single crystals between – 196° and 1000°C. The surface energy for cleavage was determined from many tests to be 2500 erg/cm2. A transition from pure cleavage to general yielding at the crack-tip was found to occur over several degrees centigrade. The brittle-to-ductile transition was rate dependent and obeyed an activation energy close to that for thermally-activated dislocation glide. A mechanism based on crack-tip blunting through dislocation nucleation and glide was developed to explain the abruptness of the brittle-to-ductile transition. The crack-tip dislocation arrangements were analysed by Lang X-ray topography.