Dislocation-free Crystals Research Articles

Dislocation behavior in heavily germanium-doped silicon crystal

Dislocation-free heavily Ge-doped Czochralski (CZ)-Si crystal growth using a heavily Ge-doped Si seed has been investigated. Dislocations due to thermal shock were suppressed in a seed 7×7 mm 2 in cross-section when Ge concentration in the seed exceeded 9×10 19 atoms/cm 3. When Ge concentration in the grown crystal was 5.7×10 20 atoms/cm 3, cellular growth occurred, and this concentration was a limit for heavily Ge-doped Si single crystal growth with a growth rate of about 1 mm/min. Resistivity in the crystal results in B or P doping could be controlled precisely in spite of using a heavily Ge-doped Si seed for growing a dislocation-free CZ-Si crystal without Dash necking.

Carrier recombination at single dislocations in GaN measured by cathodoluminescence in a transmission electron microscope

We study radiative and nonradiative recombination at individual dislocations in GaN by cathodoluminescence performed in a transmission electron microscope. The dislocations are produced by indentation of dislocation free single crystals and have a-type Burgers vectors (b=1/3〈112̄0〉). They are aligned along 〈112̄0〉 directions in the basal plane. Our direct correlation between structural and optical properties on a microscopic scale yields two main results: (i) 60°-basal plane dislocations show radiative recombination at 2.9 eV; (ii) screw-type basal plane dislocations act as nonradiative recombination centers. We explain the nonradiative recombination by splitting this dislocation into 30° partials that have dangling bonds in the core. The dissociation width of these dislocations is <2 nm.

Optical anisotropy and strain-induced birefringence in dislocation-free silicon single crystals

Birefringence measurements, using a scanning infrared polariscope (SIRP) with high sensitivity, have been carried out in as-grown dislocation-free silicon single crystal ingots. A small amount of birefringence due to 〈110〉 optical anisotropy, which is predicted not by the classical optics theory but by the Lorentz's spatial dispersion theory, is observed in the θ– Z optical configuration, for which a probing polarized light is introduced from the as-grown cylindrical ingot surface and then the polarization of the light transmitted through the opposite surface is analyzed. On the other hand, in the R– θ optical configuration, for which the probing polarized light is introduced along the 〈001〉 crystal growth direction from the (001) sliced and polished surface and then the polarization of the light transmitted through the opposite (001) surface is analyzed, the birefringence is still observed although it is extremely small. It is found that this 〈001〉 optical anisotropy is not constant over the (001) cross-section of the ingot but consists of two different components, i.e. a symmetric component distributed over the whole sample, probably caused by point defects, and an asymmetric component distributed randomly near the peripheral region, related to dents and chips on the as-grown cylindrical surface.

Growth of Low Etch Pit Density (EPD) InP Crystals

Two-inch and 3-inch diameter S-doped dislocation-free (DF) (Dislocation density < 500/cm2) InP crystals were grown by the differently modified liquid-encapsulated Czochralski (LEC) method. Two-inch-diameter InP crystals were grown by the double thermal baffle method (DTB) and 3-inch-diameter crystals were grown by the phosphorus vapor controlled LEC method (PC-LEC). The DF S-doped InP crystals become somewhat rectangular in shape and the faceting on the body of the ingots takes place during the growth. The length of the edge facets in DF crystals is much longer than that of the Sn-doped InP crystals of which EPD is relatively high. We think that the difference in facet length can be explained by the difference in supercooling. To grow the DF single crystals, it is necessary to use the stoichiometric polycrystals without certain specific impurities.

Semiconductor silicon at the threshold of twenty-first century

The strategy of the further development of silicon technology in the near future is analyzed in light of the problems of semiconductor electronics. The main tendencies in synthesis of dislocation-free single crystals of large dimensions with a controlled concentration of microdefects are considered. Promising directions of future development of the technology for manufacturing thin epitaxial films, including Si1−xGex Si heteroepitaxial films with low dislocation concentrations, are discussed. Considerable attention is paid to the prospects for technologies used in synthesis of high-quality silicon-on-insulator structures. The problems of silicon-based optoelectronics associated with manufacturing device structures for highly efficient radiation sources are analyzed in terms of materials science. The characteristic features of the present state in technology and materials science of silicon, the most important semiconductor material, are discussed.

The critical temperature in the initiation of plastic strain in nearly dislocation-free crystals of NiAl

The plastic deformation in nearly dislocation-free NiAl single crystals loaded along 〈0 0 1〉 is initiated at a well-defined temperature. This is found by the anisothermal creep test. The initiation temperature is rate-independent at low heating rates and defines a critical point.

Dislocations and 90°-twins in LEC-grown InP crystals

The results of dislocation density and 90°-twins investigations in 〈1 1 1〉-oriented InP crystals grown by the LEC technique with two different axial temperature gradients, d T/d z=260 and 100 K/cm, are reported. Estimation of the maximum diameters ( D max) of dislocation-free crystals, which can be grown with a given d T/d z, is made. It is discovered that 90°-twin formation for a given d T/d z takes place in a narrow range of crystal diameters ( D T), and D T≈ D max for both d T/d z=260 and 100 K/cm. By the selective etching of the crystal axial section, crystallization front shape in the 90°-twin region is revealed. It is discovered that 90°-twin formation coincides with the morphological signs of a change from crystal dislocation-free growth mechanism to a dislocation growth mechanism. A possible mechanism of influence of the dislocations on twin formation in the framework of the theory of the crystals lateral growth from the melt is discussed.

Selection of crack-tip slip systems in the thermal arrest of cleavage cracks in dislocation-free silicon single crystals

New B–D fracture transition experiments in dislocation––free Si single crystals are described based on arrest of cleavage cracks propagating up a temperature gradient. Combined etch pitting and Berg–Barrett imaging shows that the fracture transitions are accomplished exclusively on planes with the most advantageous conditions for dislocation nucleation from crack-tip cleavage ledges.

Heating rate dependence of melting of silicon: An in situ x-ray topography study

In situ observations of the melting processes of dislocation-free silicon crystals were carried out using x-ray topography technique. Heating procedures with various heating rates were used in the experiments. Dot contrasts were observed during the melting process at a high heating rate, while they could not be found at a low heating rate. It was found that the melting process at a high heating rate is spatially inhomogeneous, while that at a low heating rate is homogeneous. It was also found that the oxygen concentration in the sample plays an important role in the formation of dot contrasts during the melting process. The dot contrasts were assumed to originate from the dislocation loops around the oxygen precipitates.

Growth of silicon crystal with a diameter of 400 mm and weight of 400 kg

Since 1996, we have been investigating the crystal growth of 400-mm silicon crystals as the next generation of silicon wafer size after 300 mm. The first dislocation-free crystal was grown in 1998, and the heaviest dislocation free crystal ever, weighing 413 kg, was safely grown in 2000 using a crystal suspending system. In this paper, we describe an experimental study on large-diameter silicon crystal growth, its growth conditions, and the crystal properties of 400-mm silicon crystals.

Variation of electrical properties on growth sectors of ZnO single crystals

We have grown almost dislocation-free ZnO crystals by the hydrothermal method. The variation of electrical properties on growth sectors of these crystals was studied by means of I– V and 1/ C 2– V measurement. Gold contacts were made at the polar faces on each growth sector. In the (0 0 0 1 ̄ ) faces [O surface] of all the sectors, clear rectifying action was observed. In the (0 0 0 1) faces [Zn surface] of all sectors, weak rectifying action or nearly ohmic characteristics were observed. These results indicate that the O surfaces tend to induce intrinsic defects like O vacancies and the rectifying characteristics become strong, while Zn surfaces tend to form a metallic face so that the Au contacts become ohmic. The variation of I– V and 1/ C 2– V characteristics on the growth sectors showed that the contacts of m growth sector have better characteristics than those of other sectors.

Flow driven by Marangoni convection and rotating magnetic field in a floating-zone configuration

This paper treats the axisymmetric flo w driven by Marangoni convection and a Rotating Magnetic Field (RMF) in a Floating-Zone configuration. For a low Prandtl number liquid, and different Marangoni values, we investigate the evolution of the flo w as the intensity of the RMF is increased. It evolves from a Marangoni dominated flo w to a RMF dominated flo w . We particularly emphasise and explain the transition re gion where both sources of motion surprisingly tend to cancel each other. Introduction Float-Zone is the method of choice to produce high-purity silicon crystals. A polycrystalline rod is moved through a heater. As the melt solidifies on a crystal seed a single crystal grows. This containerless technique yields dislocation-free crystal. The presence of thermally induced surface tension gradients along the free sur- face leads to a strong conv ection (called Marangoni convection) in the melt that produces undesirable macro and microsegregation. A drastic reduction of microse gregation due to a rotating magnetic field (RMF) in a crystal grown with floating-zone technique has been shown e xperimentally (1). The effect of the RMF is to produce a prescribed azimuthal body force in the melt. In the e xperiments (1), the flo w is in a regime where realistic numerical simulation is still difficult to achiev e. We study a simplified situation to un- derstand some of the mechanisms that occur when the flo w is dri ven by both sources of motion. The classical model for the study of Marangoni convection in a liquid bridge is to consider the liquid suspended between two planar circular isothermal disks at different temperature (2), (3). The b uoyant convection is usually neglected when compared to the Marangoni convection. This situation is often referred to as a half-zone. While the free- surface position is not known a-priori, a further simplification is to consider its location to be at a constant radius. In our study, we keep most of half-zone simplifications with the notable e xception that we take both disks to be at melting temperature and a heat flux is prescribed along the free surf ace. Such models have already been proposed (4), (5), (6). We use the same parabolic e xpression for the heat flux as the latter. 1. Pr oblem formulation We use cylindrical coordinates with the axis along the centerline of the cylinder with the origin at the middle of the liquid region and unit vectors . The free surface is located at a radius and we fix the distance between the feed rod and the crystal at . We make the assumption that the flo w remains axisymmetric and steady. We nor- malize length by and velocity by , where is the kinematic viscosity of the fluid. We use the vorticity , stream-function formulation where and the velocity . We introduce the

The growth technology for 300 mm single crystal silicon

The fabrication technique for 300 mm silicon single crystals and wafers is the central topic of silicon material research recently. The study on the growth technique of 300 mm silicon ingots has been developed in our institute since 1997. The research mainly focuses on the following aspects: (1) process conditions for fabrication of the dislocation-free silicon single crystal; (2) oxygen content in the silicon crystals; (3) elimination of oxidation-induced stacking faults (OSF) ring in the crystal. It is found that the hot zone configuration, parameters of growth process, magnetic field, heat shield and so on have an important effect on the perfection of crystals and the impurity concentration in the obtained crystals. The 300 mm silicon ingots can be obtained repeatedly. The impurities in the crystals can be effectively controlled. Effect of cusp magnetic field on the crystal growth has been investigated. The role of heat shield in hot zone has also been discussed.

Dislocation-Free Czochralski Silicon Crystal Growth without Dash Necking

Dislocation-free silicon crystals which underwent boron and phosphorus doping were grown by the Czochralski (CZ) method without Dash necking. The boron concentration limit in a silicon seed 7×7 mm2 in cross section without dislocations due to thermal shock was 1×1018 atoms/cm3 in ordinary CZ silicon-crystal growth. The maximum admissible discrepancy of boron concentration in the seed and grown crystal was 7×1018 atoms/cm3 without dislocations due to lattice misfit in the grown crystal. Silicon seeds with a boron concentration of 3×1018 atoms/cm3 were used to grow CZ silicon crystals from lightly boron-doped (p-type) or phosphorus-doped (n-type) silicon melt, yielding dislocation-free silicon crystals without the need for Dash necking. Heavily boron-doped silicon seed should thus be applicable in growing other practical lightly doped dislocation-free CZ-silicon crystals without the need for Dash necking.

The deformation regimes of the yield point of silicon

The upper yield point of undoped floating-zone silicon has been investigated. The measurements were performed on dislocation-free single crystals deformed at temperatures between 800 and 1300°C and a strain-rate range extending over three orders of magnitude. The upper yield point emerges up to 1250°C. In principle, the data reflect the behaviour of the lower yield point, thus confirming the existence of a novel deformation regime of silicon at high temperatures and small strain rates. There are, however, features which resemble the behaviour of highly doped material to some extent. This surprising similarity raises questions concerning the interpretation of the different deformation regimes observed in undoped and doped silicon.

Dislocation multiplication in silicon at the onset of plasticityobserved by in situ synchrotron x-ray topography

In situ observations by synchrotron x-ray topography were performed oninitially dislocation-free silicon single crystals deformed in creepconditions at temperatures between 975 K and 1075 K, and tensile stressesequal to 22 MPa or 44 MPa, in order to study the multiplication ofdislocations during the very first stages of plastic deformation.It could be seen that the first dislocations, created at Vickers micro-indentsor at residual surface damage, did not develop in a strictly planar way:prismatic half loops, gliding simultaneously on two {111} planes, werecommonly observed. Cross-slip events appeared to be quite frequent, in thebulk as well as at free surfaces. Groups of similar dislocations soonexhibited irregular shapes with cusps and trailing dipoles, which was taken asan indication that they developed jogs during their motion. Severalconfigurations of dislocation sources formed by the mobile dislocations wereobserved and are described in detail. The formation of new sources usuallyinvolved cross-slip. The role of jogs formed by forest-cutting seemsimportant. The efficiency of sources was strongly limited by the lack ofstability of the cross-slipped segments, which acted as poles for theFrank-Read mechanism.

Growth of dislocation-free ZnSe single crystal by CVT method

ZnSe single crystals with a diameter of 12 mm and a length of 28 mm were grown by the CVT method using iodine as a transport agent. The ampoule wall, which has direct contact with the crystal during growth, was formed of pBN. The seed crystal, which was the CVT grown ZnSe single crystal with a reduced dislocation density (EPD) of less than 1×10 4 cm −2, was used. The seed crystal was protected against thermal stress from the ampoule end wall by inserting the undoped polycrystalline ZnSe between the back of the seed crystal and the ampoule end wall. The EPD of the grown ZnSe crystal was less than 1×10 4 cm −2 even near the seed crystal, and reduced to 0 at the tail part of the crystal. The shallow pits were found to exist on the etched surface of dislocation-free part. The dislocation-free part was annealed in Zn atmosphere, and crystallographic, electrical and optical characterizations were evaluated in relation to the annealing conditions.

Anisotropy of fields of stress in Si monocrystals with ordered dislocation structure

An attempt is made with X-ray triple crystal diffractometry to detect anisotropy of X-ray scattering by a structure consisting of a number of parallel dislocations, introduced into silicon by specially controlled sample deformation. Diffuse component scattering increased if the plane of scattering was perpendicular to the direction of dislocations ( ϕ=90°). The magnitude of this effect increases with increasing density of the introduced dislocations and depends on the direction of their Burgers vectors. The respective changes of the equal-intensity contours of X-ray scattering near reciprocal lattice points for the 111 reflection are investigated. The magnitudes of coherent and diffuse components of integral reflectivity were obtained experimentally. This yields quantitative information on the diffraction characteristics of structural perfection of the material. The dependencies of these characteristics are given, as well as of half-widths of a principal peak of a diffraction curve, on the angle of sample orientation relative to the X-ray beam ϕ and ϑ B. A comparison of appropriate data with those obtained for dislocation-free crystals of non-crucible zone melting silicon is carried out. The results obtained are discussed within the framework of existing theories of X-ray scattering and dislocation complexes.

Dislocation-free B-doped Si crystal growth without Dash necking in Czochralski method: influence of B concentration

Dislocation-free Si crystals have been grown successfully from heavily B-doped Si melts by Czochralski (CZ) method without the Dash necking process. No dislocation was introduced in the heavily B-doped Si seed during dipping and no dislocation was generated in the grown crystal due to lattice misfit between the seed and grown crystal when the B concentration is the same in both the Si seed and grown crystal. These results show that the Dash necking process is unnecessary in heavily B-doped Si crystal growth. It is found that the limit of the B concentration in the Si seed for growing dislocation-free CZ-Si crystals without Dash necking is in the order of 10 18 atoms/cm 3, corresponding to a resistivity of several tens of mΩ cm.

Ultrasound-induced surface hardening of dislocation-free silicon

The effect of ultrasonic treatment on the microplastic properties of a near-surface layer in dislocation-free silicon single crystals was studied using [111]-oriented p-Si samples with artificial dislocation rosettes. The ultrasonic processing resulted in the formation of an approximately 100-µm-thick hardened near-surface layer and the emergence of point-defect pileups of the vacancy and/or vacancy-impurity cluster type on the sample surface. Possible mechanisms of the observed phenomena are discussed.