Boron segregation control in silicon crystal ingots grown in Czochralski process

Boron-doped silicon single crystals of 207 mm diameter with various growing conditions are grown from a large amount of the melt in the cusp-magnetic Czochralski method, and the effects of growing parameters on dopant concentrations in the crystals are experimentally investigated. Equilibrium distribution coefficient of boron calculated by BPS model is 0.716. With the crystal rotation (ω) of 13 rpm and the crucible rotation of , the effective distribution coefficient (k_e) is 0.751 in zero magnetic strength and increases up to 0.78 in the magnetic strength of 640 G. For , there is no significant influence of ω on k_e. With , k_e is almost unity. The experimental results are compared with theory.     

Mechanochemical–hydrothermal synthesis of hydroxyapatite from nonionic surfactant emulsion precursors

Nanocrystalline hydroxyapatite [HA, Ca₁₀(PO₄)₆(OH)₂] powders were synthesized by the mechanochemical–hydrothermal method using emulsion systems consisting of aqueous phase, petroleum ether (PE) as the oil phase and biodegradable Tomadol 23–6.5 as the nonionic surfactant. (NH₄)₂HPO₄ and Ca(NO₃)₂ or Ca(OH)₂ were used as the phosphorus and calcium sources, respectively. The calcium source and emulsion composition had significant effects on the stoichiometry, crystallinity, thermal stability, particle size and morphology of final products. Disperse HA crystals with a 160 nm length and aspect ratio of ca. 6 were formed in an emulsion system containing 10 wt% PE, 60 wt% water and 30 wt% surfactant. The HA particles had needle morphology with a specific surface area of . With this technique, HA nanopowders with specific surface areas in the range of 72– were produced.     

Formation of twinning-superlattice regions by artificial stacking of Si layers

We report about the formation of twinning-superlattice regions in Si epitaxial layers grown by molecular beam epitaxy on Si(1 1 1)()R30°-B surfaces. Twinning-superlattice regions were formed by periodical arrangement of 180° rotation twin boundaries along [1 1 1]-direction and are only separated by a few nanometers. The preparation method consists of repeating several growth, boron-deposition and annealing cycles on boron-predeposited undoped Si substrates. It is shown that the amount of subsurface boron and the growth mode influence the formation of twin boundaries. Only the nucleation of Si on the Si(1 1 1)()R30°-surface covered by at least ML boron results in the formation of 180° rotation twins. The size of superlattice regions is restricted by surface morphology. However, the presented technology should also be suitable to prepare a new type of semiconductor heterostructure based on Si polytypes.     

Synthesis of superparamagnetic Mn3O4 nanocrystallites by ultrasonic irradiation

Nanocrystalline Mn₃O₄ has been synthesized by ultrasonic irradiation of Mn acetate solution in water. Analysis of its X-ray diffraction data shows formation of a phase-pure compound with an average particle size of about 15 nm. DC magnetization measurements as a function of temperature and field show a reduced ferrimagnetic transition temperature as compared to those reported for the bulk , and a subsequent observation of superparamagnetic behavior at 40 K. The observed magnetic properties are suggestive of formation of a single domain magnetically ordered Mn₃O₄ nanoparticles below their ferrimagnetic transition temperature.     

Nucleation of AlN on SiC substrates by seeded sublimation growth

The nucleation of aluminum nitride (AlN) on silicon carbide (SiC) seed by sublimation growth was investigated. Silicon-face, 8 off-axis 4H-SiC (0 0 0 1) and on-axis 6H-SiC (0 0 0 1) were employed as seeds. Initial growth for 15 min and extended growth for 2 h suggested that 1850 °C was the optimum temperature of AlN crystal growth: on an 8 off-axis substrate, AlN grew laterally forming a continuous layer with regular “step” features; on the on-axis substrate, AlN grew vertically as well as laterally, generating an epilayer with hexagonal sub-grains of different sizes. The layer's c-lattice constant was larger than pure AlN, which was caused by the compression of the AlN film and impurities (Si, C) incorporation. Polarity sensitive and defect selective etchings were performed to examine the surface polarity and dislocation density. All the samples had an Al-polar surface and no N-polar inversion domains were observed. Threading dislocations were present regardless of the substrate misorientation. Basal plane dislocations (BPDs) were revealed only on the AlN films on the 8 off-axis substrates. The total dislocation density was in the order of when the film was 20– thick.     

Growth and optical absorption spectra of ZnO films grown by pulsed laser deposition

ZnO films on Al₂O₃ substrate were grown by using a pulsed laser deposition method. Through photoluminescence (PL) and X-ray diffraction (XRD) measurements, the optimum growth conditions for the ZnO growth were calculated. The results of the XRD measurement indicate that ZnO film was strongly oriented to the c-axis of hexagonal structure and epitaxially crystallized under constraints created by the substrate. The full-width half-maximum for a theta curve of the (0 0 0 2) peak was 0.201°. Also, from the PL measurement, the grown ZnO film was observed to be a free exciton, which indicates a high quality of epilayer. The Hall mobility and carrier density of the ZnO film at 293 K were estimated to be 299 cm²/V sec and , respectively. The absorption spectra revealed that the temperature dependence of the optical band gap on the ZnO films was − .     

Study on optimal growth conditions of a-plane GaN grown on r-plane sapphire by metal-organic chemical vapor deposition

Non-polar a-plane GaN thin films were grown on r-plane sapphire substrates by metal-organic chemical vapor deposition. In order to obtain a-plane GaN films with better crystal quality and surface morphology, detailed comparisons between different growth conditions were investigated. The results showed that high-temperature and low-pressure conditions facilitating two-dimensional growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best mean roughness of the surface morphology was 10.5 Å. Various thickness values of AlN nucleation layers and the V/III ratios for growth of the a-plane GaN bulk were also studied to determine the best condition for obtaining a smooth surface morphology of the a-plane GaN layer.     

Diffusion of vanadium in GaAs

The diffusion of Vanadium has been studied in V-doped GaAs layers (GaAs:V) grown by Metal-Organic Chemical Vapour Deposition (MOCVD) using secondary ion mass spectroscopy (SIMS). The vanadium (V) concentration profiles of sandwiched structures made of alternatively undoped and V doped GaAs layers have shown a concentration independent diffusion coefficient (D_V) for varying V doping levels from 10¹⁸ to 10¹⁹ cm⁻³. Measurements of D_V at 550, 615 and 680 °C indicate that the temperature dependence of D_V can be represented by the Arrhenius equation:  cm² s⁻¹. It is suggested that V diffuses via interstitial sites.     

Growth of single crystals of the new double perovskite Ba2HoRu1−xCuxO6 from high temperature solutions

Single crystals of Ba₂HoRu_1−xCu_xO₆ have been grown from high temperature solutions using PbO–PbF₂ as solvent in the temperature range 1150–1250 °C. Crystals with a six sided plate like morphology measuring up to 3 mm across and 0.5 mm thick and polyhedral habit measuring up to 2 and 1 mm in thick mass were obtained. Powder X-ray diffraction patterns obtained on the crystals were indexed to give a monoclinic space group P2₁/n with lattice parameters a=5.875(2), b=5.874(3), c=8.960(1) and β=89.995(2)°. The crystals with x=0 show a single anomaly at 6.5 K corresponding to an antiferromagnetic phase with . The crystals containing Cu show additional anomalies at 18 and 48 K. The SEM and EDS analysis reveals a 2116 phase.     

Kinetics of dopant incorporation in GaAs grown by organometallic vapor-phase epitaxy

A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal–Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p_Ga (which is proportional to the growth rate) in agreement with data on S_As, Zn_Ga, and Si_Ga where p_Ga is the partial pressure of trimethylgallium in the input gas stream.     

Some aspects on thermodynamic properties, phase diagram and alloy formation in the ternary system BAs–GaAs—Part II: BGaAs alloy formation

We present a detailed analysis of the thermodynamics of the BGaAs alloy formation taking into account the question of boron solubility and Gibbs free energy change. We also predict a Gibbs free energy change for the gas phase formation of BAs to be compared to for GaAs. We show that the experimental boron solubility is actually an open question both theoretically and experimentally, while the maximum concentration obtained up to date is reaching 6–7%. It thus follows that despite the low boron solubility, the Gibbs free energy change for the alloy formation is dominated by the chemical term over the mixing energy change. We could deduce order of magnitude for the ratio of the boron partial pressure and that of gallium. P_B could be estimated as being always much lower than P_Ga; it is shown that the alloy content is probably controlled by the Ga equilibrium partial pressure.     

Some aspects on thermodynamic properties, phase diagram and alloy formation in the ternary system BAs–GaAs—Part I: Analysis of BAs thermodynamic properties

Owing to the lack of available thermodynamic data based on experimental measurements of heat capacity, decomposition reaction or vapour pressure measurements, the problem of BAs stability is considered. We propose a new set of thermodynamic data for enthalpy of formation, entropy and Gibbs free energy of Bas compound. By using thermodynamic database, our approach is based on the semi-empirical trends and analogy in the variation of those quantities for several binary series in different III–V systems like arsenides, nitrides and phosphides. Thus, the values for BAs were derived by extrapolation from Al to boron-based compounds (BAs, BP and, BN). For pure BAs(s), we predict a low enthalpy of formation in the standard state of at 300 K and a Gibbs free energy of indicating a lower stability of this compound than GaAs. Those values are contradictory discussed with trends in the cohesive energy of several III–V systems. A cohesive energy of 900 kJ/mol (9.4 eV) is proposed in agreement with Philips's rule.     

The tri-methyl-Sb flow and the surfactant time effect on InGaAsN/GaAs-strained MQWs grown by MOCVD

The tri-methyl-Sb flow and the surfactant time dependence of photocurrent (PC) spectra was studied on InGaAsN/GaAs-strained multiple quantum wells (MQWs) structures grown by using metalorganic chemical vapor deposition (MOCVD). The structural properties of InGaAsN/GaAs-strained MQWs were investigated by using high-resolution X-ray diffraction (HRXRD). In the case of InGaAsN/GaAs-strained MQWs, an increase in compressive strain from an analysis of the satellite peaks in HRXRD was observed on increasing the tri-methyl-Sb flow and the surfactant time. For InGaAsN/GaAs-strained MQWs, the peaks observed in the photocurrent spectra were preliminarily assigned to electron–heavy hole (e₁–hh) and electron–light hole (e₁–lh) fundamental excitonic transitions. Their peaks are red-shifted with increasing tri-methyl-Sb flow and surfactant time. But the photocurrent peak is blue-shifted at the surfactant time of . It seems to be due to the improvement of structure properties at interface owing to a surfactant-suppressing surface diffusion phenomenon during growth. We compared this with the result of the experimental energies for InGaAsN/GaAs-strained MQWs.     

Controlled growth and kinetics of porous hydroxyapatite spheres by a template-directed method

Porous hydroxyapatite (HA) spheres with high purity of phase and well-controlled pore size were grown by a template-directed method. We studied for the initial concentration of Ca–P how to control the chemical component of the products, and for the concentration of template how to control the aperture and the morphology of porous HA spheres. The experimental results indicated that the lower concentration of Ca–P was prone to pure HA phase and the aperture decreased gradually with the increase of the concentration of template. Correspondingly, the crystallization thermodynamics and template-directed growth kinetics were discussed in details. The solubility isotherms of HA and dicalcium phosphate (DCPD) were calculated based on classical crystallization theories of thermodynamics. The results suggested that there was a critical concentration of in the case of Ca:P=5:3 and thus DCPD could be avoided only when in this given reaction system. Kinetic analysis of HA crystal growth revealed that the template depressed the interfacial potential energy E, then enhanced the roughness on the surface of crystal nucleus and directed HA crystal to selectively grow along the [0 0 0 1] direction, and consequently governed the aperture of porous HA spheres. The experimental results were in agreement with the theoretical analysis.     

Arsenic cross-contamination in GaSb/InAs superlattices

We have investigated the cross-contamination of As in GaSb/InAs superlattices. We demonstrate a method of varying the lattice constant of the superlattice. By controlling the As background pressure in the growth chamber, the strain can be controlled to about 0.01%, corresponding to As cross-incorporation variations of about ±1%. The distribution of As is investigated by X-ray diffraction and cross-sectional scanning tunneling microscopy, and the critical thickness is obtained.     

Diffusion of Zn in stoichiometric LiTaO3

As stoichiometric LiTaO₃ (LT) draws a considerable attention for integrated optical waveguide devices, we have investigated Zn diffusion into this material by diffusing 70- nm-thick ZnO films deposited on y-cut LT substrates at 700–900 °C under various atmospheres. It was observed that the surface quality was very sensitive to pressure, but weakly affected by other diffusion conditions such as temperature and atmosphere. While the surface degraded, being covered with some residuals after heat treatment at the atmospheric pressure, it was very smooth and clear when the pressure was lowered below about 10 Torr. Another feature of Zn-diffused stoichiometric LT is that the crystal maintains its transparency even after diffusion at a pressure as low as 0.1 Torr, thus without a post-annealing step required. The diffusion coefficient varied from D=1.1×10^-2 to 5.5×10⁻¹ μm²/h in the given temperature range, with an activation energy of .     

Study of the hydrodynamic instabilities in a differentially heated horizontal circular cylinder corresponding to a Bridgman growth configuration

We are interested in determining the origin of the instabilities occurring in a metallic liquid (Prandtl number Pr=0.026) contained in horizontal circular cylinders heated from the end-walls. Our approach by direct numerical simulation (DNS) allows the determination of the transition thresholds for different aspect ratios varying from 1.5 to 10 as well as a precise characterization of the nature and structure of the new flow regimes close to the thresholds. In order to understand the mechanisms of flow transition, fluctuating energy analyses close to the threshold have been performed. The main contributions have been determined and localized in the cavity: shear has been found as the main instability factor but the way it acts is different according to the aspect ratio.     

Determination of kinetic parameters of crystal growth rate of borax in aqueous solution by using the rotating disc technique

Growth rate of polycrystalline disc of borax compressed at different pressure and rotated at various speed has been measured in a rotating disc crystallizer under well-defined conditions of supersaturation. It was found that the mass transfer coefficient, K, increased while overall growth rate constant, K_g, and surface reaction constant, k_r, decreased with increasing smoothness of the disc. It was also determined that kinetic parameters (k_r,r,K,g) of crystal growth rate of borax decreased with increasing rotating speed of the polycrystalline disc. The effectiveness factor was calculated from the growth rate data to evaluate the relative magnitude of the steps in series bulk diffusion through the mass transfer boundary layer and the surface integration. At low rotating speed of disc, the crystal growth rate of borax is mainly controlled by integration. However, both diffusion and integration steps affect the growth rate of borax at higher rotating speed of polycrystalline disc.     

Densities of Li2O–B2O3 melts

The densities have been systematically measured in xLi₂O–(1−x)B₂O₃ melts of different compositions with Li₂O content varying from x=0 to 0.68 from their respective melting points up to about 1450 K with a modified Archimedean method. The density decreased with increasing temperature for all the melts measured in this work. When x<0.15, the plot of temperature versus density could be well fitted by a quadratic polynomial function, and when x0.15, density decreased linearly with increasing temperature. At a fixed temperature, the density of the melts increased rapidly with Li₂O content, went through a maximum at about x=0.333 (Li₂O–2B₂O₃), and then decreased slowly as Li₂O content was further increased. In addition, the volume expansion coefficient (β) was calculated based on the densities measured in this work, and it was found that a maximum value appeared in the dependence of β on the molar ratio of Li₂O at about x=0.333.     

A study of the degree of relaxation of AlGaN epilayers on GaN template

The strain state of 570 nm Al_xGa_1−xN layers grown on 600 nm GaN template by metal organic chemical vapor deposition was studied using Rutherford backscattering (RBS)/channeling and triple-axis X-ray diffraction measurements. The results showed that the degree of relaxation (R) of Al_xGa_1−xN layers increased almost linearly when x0.42 and reached to 70% when x=0.42. Above 0.42, the value of R varied slowly and Al_xGa_1−xN layers almost full relaxed when x=1 (AlN). In this work the underlying GaN layer was in compressive strain, which resulted in the reduction of lattice misfit between GaN and Al_xGa_1−xN, and a 570 nm Al_xGa_1−xN layer with the composition of about 0.16 might be grown on GaN coherently from the extrapolation. The different shape of (0 0 0 4) diffraction peak was discussed to be related to the relaxation.