PBN Crucibles Research Articles

Single crystal growth of small-angle-grain-boundary-free Mg2Si via vertical Bridgman method

Mg2Si single crystal was grown via vertical Bridgman method using pyrolytic boron nitride (pBN) crucibles coated with boron nitride (BN). No stress was imposed from the liquid/ solid interface (molten Mg2Si/ BN-coated crucible surface) during the solidification leading to a small angle grain boundary free crystal. As a result of X-ray rocking curve measurement of the cut wafer, in-plane high crystallinity was confirmed and a sharp single peak with FWHM of 44–51 arcsec was measured. The typical electron concentration of grown crystal was 6.6 × 1017 cm−3 and Hall mobility was 280 cm2/Vs. The high electron concentration was attributed to the contamination of crystal by boron from BN coating source, confirmed by glow discharge mass spectroscopic (GDMS) analysis.

Centimetric CrSi2 crystal grown by the vertical gradient Freeze method

CrSi2 ingots were grown by the Vertical Gradient Freeze (VGF) method in silica (SiO2) crucibles with boron nitride (BN) coating and in pyrolytic boron nitride (pBN) crucibles in order to minimize the sticking and the reaction with the molten Cr-Si alloy. High quality chromium disilicide single crystal was obtained with a mosaicity of 1–2° using pBN crucible with a thermal gradient of 0.6 K/mm and a growth rate of 10 mm/h. To recycle the crucibles and so to reduce the production costs, pBN crucibles were cleaned with hydrofluoric acid solution. As a result of this treatment, it was not possible to obtain CrSi2 single crystals due to a modification of the crucible surface and the subsequent increase of boron compounds in the melt during the growth. The effect of the growth conditions on the microstructure of polycrystalline sample was also investigated using the texture analysis technique.

Nanopipe formation as a result of boron impurity segregation in gallium nitride grown by halogen-free vapor phase epitaxy

The work reported herein demonstrated that nanopipes can be formed via a surfactant effect, in which boron impurities preferentially migrate to semipolar and nonpolar facets. Approximately 3 μm-thick GaN layers were grown using halogen-free vapor phase epitaxy. All layers grown in pyrolytic boron nitride (pBN) crucibles were found to contain a high density of nanopipes in the range of 1010 to 1011 cm−2. The structural properties of these nanopipes were analyzed by X-ray rocking curve measurements, transmission electron microscopy, and three-dimensional atom probe (3DAP) tomography. The resulting 3DAP maps showed nanopipe-sized regions of boron segregation, and these nanopipes were not associated with the presence of dislocations. A mechanism for nanopipe formation was developed based on the role of boron as a surfactant and considering energy minima. A drastic reduction in the nanopipe density was achieved upon replacing the pBN crucibles with tantalum carbide-coated carbon crucibles. Consequently, we have confirmed that nanopipes can be formed solely due to surface energy changes induced by boron impurity surface segregation. For this reason, these results also indicate that nanopipes should be formed by other surfactant impurities such as Mg and Si.

Influence of carbon coated pBN crucible on crystal growth of Cd0.9Zn0.1Te for radiation detector applications

In the Bridgman and Vertical Gradient Freeze (VGF) techniques, it is common to use a high purity crucible for crystal growth. One disadvantage of pBN crucibles is associated with the crucible material interacting with the melt during the growth cycle. Using pBN crucibles for the growth of CZT, we have observed that the crucible does in fact interact with the CZT melt. To prevent this interaction, a vacuum carbon coating system for applying a carbon coating to pBN crucibles has been developed. The effects of crucible use with time are studied, as are the compositional and device properties of the bulk material. GDMS measurements are used to investigate on broron and nitrogen content, among other trace impurities found in the crystal. Devices harvested from ingots grown using cc-pBN exhibit high resistivity and good functionality as room temperature gamma ray detectors.

Growth of Undoped GaAs Single Crystal by Pulling-Down Method

Undoped GaAs single crystal has been grown in PBN crucibles by the pulling-down method. The temperature profile of the furnace was optimized with a narrow melting zone and a small temperature gradient at the solid-liquid interface. Quartz ampoules were used to protect the evaporation of As during the growth and the deformation of the ampoule was discussed as a function of temperature, time and pressure differential. A Ø56 mm×70 mm GaAs crystal with nearly 100 % single crystalline yield was obtained. X-ray rocking curve analysis revealed the excellent crystalline quality. The average EPD and electrical properties of the crystal were tested comparable to those of the crystal produced by the VGF method. Therefore, the pulling down method was a feasible approach for GaAs crystal production.

Detached growth of germanium by directional solidification

The conditions of detached solidification under controlled pressure differential across the meniscus were investigated. Uncoated and graphite- or BN-coated silica and pBN crucibles were used. Detached and partly detached growth was achieved in pBN and BN-coated crucibles, respectively. The results of the experiments are discussed based on the theory of Duffar et al.

Characterization of InP grown by LEC using glassy carbon, silica and PBN crucibles

Undoped InP single crystals were grown by liquid-encapsulated Czochralski method (LEC) using glassy carbon, silica and PBN crucibles. The samples were characterized by Hall and resistivity measurements, photoluminescence at 2 K and glow discharge mass spectroscopy. The residual impurity concentrations for InP grown using glassy carbon or silica crucible are of the same order of magnitude but both higher than that for InP grown with PBN crucibles. All samples exhibit good optical quality. The main acceptor impurities detected in all samples were C and Zn, while the main donors were S and Si. The InP grown from the glassy carbon crucible has the lowest C concentration and the main dopant detected in this sample was S originating from the crucible.

Growth of InP by LEC using glassy carbon crucibles

Abstract Undoped InP single-crystals were grown by the LEC method using glassy carbon crucibles. The samples were grown in the 〈100〉 direction; they were of 100 g weight and 25 mm diameter. The residual carrier concentration at room temperature was about 1.0 × 1.0 16 cm −3 and the glassy carbon crucible was shown to be fully reusable. For comparison, with the same growth conditions and starting materials, single crystals were grown using silica and PBN crucibles and their residual carrier concentration were, respectively, 4.1 × 10 15 and 3.3 × 10 15 cm −3 .

Influence of pyrolytic boron nitride crucibles on GaAs crystal growth process and crystal properties

The influence of pyrolytic boron nitride (pBN) crucibles on the GaAs liquid encapsulated Crochralski (LEC) growth process and on the crystal properties was investigated. An increased boron concentration in the crystals is found to be caused by oxidation processes between B 2O 3 · xH 2O, GaAs and impurity elements in GaAs as a function of water content and not by dissolution of boron from the crucible. Variations of pBN deposition parameters influence the texture and properties of pBN crucibles with regard to their suitability for the GaAs LEC crystal growth application. Correlations between pBN morphologies and thermal conditions of GaAs growth process and the crystal perfection were found. The best results are obtained by using so-called substrate nucleated pBN crucibles.

Minority carrier lifetimes in molecular beam epitaxy grown AlxGa1−xAs/GaAs double heterostructures doped with aluminum

Both Al-treated pBN crucibles and Al-doped Ga melts have been used to reduce Ga-cell related oval defect densities in molecular beam epitaxy (MBE) grown epilayers. This practice, although effective in reducing the oval defect density, results in small amounts of Al contamination in the grown films. In this work, we have grown diagnostic Al0.3Ga0.7As/GaAs double heterostructure (DH) devices doped with Al in order to determine the effect of Al contamination on the minority-carrier lifetime. The active region of the DH structures was doped with Al at 5×1018 atoms/cm3 to emulate the levels observed when Al-treated pBN crucibles are used. Al impurity levels and distribution profiles were characterized by secondary ion mass spectrometry, and minority-carrier lifetimes of DH devices were characterized using time-resolved photoluminescence (PL) measurements. Device structures grown with various GaAs active layer thicknesses were used to calculate the interface recombination velocity (S) and the bulk lifetime (τB). We found that Al doping of the GaAs active layer adversely affects the measured PL decay time. GaAs active layers of DH devices doped with Al exhibited poor bulk lifetimes (τB≤120 ns) limited by Shockley–Read–Hall recombination. In contrast, DH devices grown with Al-free active layers resulted in significantly improved PL decay times with bulk lifetimes as high as τB=700 ns.

Effects of total liquid encapsulation on the characteristics of GaAs single crystals grown by the vertical gradient freeze technique

Total liquid encapsulation with B 2O 3 has been used to grow 50 mm diameter GaAs single crystals in PBN crucibles in a vertical gradient freeze configuration. The B 2O 3 layer efficiently prevents direct contact between the crucible and the GaAs charge and reproducible growth of single crystals can be achieved. The effect of B 2O 3 water content on the structural and electrical characteristics of the crystals was investigated. Water vapor can be trapped betwen the crystal and the crucible affecting the surface morphology of the crystals. The water content of the B 2O 3 encapsulant was found to affect the electrical properties of the crystals in a manner similar to what is observed for growth of GaAs crystals by the liquid encapsulated czochralski technique. Crystals grown encapsulated with dry B 2O 3 have been ion-implanted with silicon. The implant activations are comparable to those obtained on LEC grown crystals. Total liquid encapsulation in vertical gradient freeze can be used to produce device quality substrates.

Preparation of molecular-beam epitaxy growth high-quality GaAs–AlGaAs quantum wells and their properties investigation

The quality of molecular‐beam epitaxy (MBE) growth GaAs–AlGaAs are essential for the properties of new type microstructural devices. Improved growth conditions in MBE have permitted the fabrication of high‐quality ultrathin microstructural materials. In this paper, we report the preparation of MBE grown high‐quality GaAs–AlGaAs quantum wells (QW’s) and their properties. The 1.2 meV FWHM of E1h indicates the high quality of the material. Growth conditions (especially growth temperature Ts and precise control of the layer thickness) and the substrate preparation are important factors for MBE growth of high‐quality ultrathin microstructural materials. The molecular‐beam sources of our MBE system are vertical type Knudsen cells employing PBN crucibles. Entire component parts of our MBE system were made in China.

Photoluminescence study of residual shallow acceptors in liquid-encapsulated Czochralski-grown InP

For nominally undoped InP crystals grown in silica, pBN, ceramic AlN, and pG crucibles by the liquid-encapsulated Czochralski (LEC) technique, residual shallow acceptors are investigated by photoluminescence measurements. Mg and Ca, contained in the InP starting materials, are found to be removed due to reactions with the B2O3 encapsulant. Zn and C, of which Zn was dominant throughout the undoped crystals, are found to be residual acceptors incorporated during LEC growth. The B2O3 encapsulant is identified as one Zn contamination source.

Thermal detection of electron spin resonance in the persistent photoconductive state of semi-insulating GaAs crystals grown from pyrolytic BN crucibles

Thermally detected electron spin resonance (TDESR) has been applied to paramagnetic defects characteristic of semi-insulating (SI) GaAs crystals grown from pyrolytic boron nitride (pBN) crucibles. A strong isotropic TDESR signal near g=2.2 and two anisotropic lines at higher fields were observed at T=4.2 K and 13 GHz after in situ optical excitation. Spin-dependent scattering of electrons, in their persistent photoconducting state, by paramagnetic defects is discussed as a possible cause of these resonances. Unsuccessful searches for this TDESR signal in semi-insulating GaAs crystals grown under non-pBN ambient conditions point to paramagnetic defects owing to the inclusion of some crucible material, e.g., nitrogen, as the source of the TDESR spectrum in pBN-GaAs.

LEC-growth and the major electrical and structural characteristics of semi-insulating gallium arsenide

Etch-pit density, mobility, Hall constant and sheet resistance have been measured in several GaAs ingots grown by LEC procedure. The main results are that: i) the dislocation density is influenced by the melt stoichiometry; ii) the sheet resistance varies monotonically along the crystal radius; iii) the mobility and Hall constant vary with temperature and behave as if one deep level (which changed its filling state according to T) were present. Moreover, it has been observed that PBN crucibles chemically react with the molten boron oxide, resulting in a contamination of the melt, which can be responsible for crystal twinning.

Boron contamination and precipitation during the growth of InP

We have examined polycrystalline and single crystal, liquid encapsulated Czochralski (LEC) grown InP for evidence of boron contamination using secondary-ion mass spectrometry (SIMS) and photoluminescence. Precipitates of boron or a boron compound have been found in InP grown by the LEC method with boric oxide (B 2O 3) encapsulation and pyrolytic boron nitride (pBN) crucibles. The density of precipatates appears to increase towards the last-to-freeze end of the boules. Neither B 2O 3 or pBN appears to be solely responsible for the observed phenomenon. At present, the source of boron contamination most consistent with our observations is the result of interaction between B 2O 3 and pBN. A diffusion coefficient of D(750°C) < × 10 -14 cm 2 s -1 for boron in InP has been determined in this work.

Undoped semi-insulating LEC GaAs: a model and a mechanism

Undoped semi-insulating GaAs grown by the high-pressure liquid encapsulated Czochralski (LEC) method has been produced for use in direct ion implantation in several laboratories. A clear understanding of the factors controlling impurity transport and compensation in these materials has been lacking to date. In this work, detailed characterization has been performed on undoped semi-insulating crystals grown from both SiO2 and PBN crucibles followed by a proposed impurity model and compensation mechanism.