Boron Nitride Crucibles Research Articles

Effects of stoichiometry on thermal stability of undoped, semi-insulating GaAs

We provide independent evidence of the effects of melt composition on the semi-insulating behavior and thermal stability of undoped GaAs crystals pulled from pyrolytic boron nitride crucibles by the liquid-encapsulated Czochralski technique. Semi-insulating crystals pulled from stoichiometric or As-rich melts show excellent stability to heat treatments, in contrast to semi- insulating Ga-rich material which exhibits p-type conversion after prolonged annealing at 860 °C. Deep level transient spectroscopy and Hall-effect measurements suggest that p-conversion is caused by outdiffusion of native As and/or Ga defects associated with the EL2 deep donors, resulting in uncompensated residual acceptors, predominantly carbon impurities at the surface. The measured mobility of undoped, semi-insulating GaAs is found empirically to be a sensitive parameter for qualifying substrates for direct ion implantation.

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.

Growth and characterization of large diameter undoped semi-insulating GaAs for direct ion implanted FET technology

The growth of large diameter, semi-insulating GaAs crystals of improved purity by Liquid Encapsulated Czochralski (LEC) pulling from pyrolytic boron nitride (PBN) crucibles and characterization of this material for direct ion implantation technology, is described. Three-inch diameter, 〈100〉-oriented GaAs crystals have been grown in a high pressure Melbourn crystal puller using 3 kg starting charges synthesized in-situ from 6/9s purity elemental gallium and arsenic. Undoped and Cr-doped LEC GaAs crystals pulled from PBN crucibles exhibit bulk resistivities in the 10 7 and 10 8 Ω cm range, respectively. High sensitivity secondary ion mass spectrometry (SIMS) demonstrates that GaAs crystals grown from PBN crucibles contain residual silicon concentrations in the mid 10 14 cm −3 range, compared to concentrations up to the 10 16 cm −3 range for growths in fused silica containers. The residual chromium content in undoped LEC grown GaAs crystals is below the SIMS detection limit for Cr (4 × 10 14 cm −3). The achievement of direct ion implanted channel layers of near-theoretical mobilities is further evidence of the improved purity of undoped, semi-insulating GaAs prepared by LEC/PBN crucible techniques. Direct implant FET channels with (1–1.5) × 10 17 cm −3 peak donor concentrations exhibit channel mobilities of 4,800–5,000 cm 2/V sec in undoped, semi-insulating GaAs substrates, compared with mobilities ranging from 3,700 to 4,500 cm 2/V sec for various Cr-doped GaAs substrates. The concentration of compensating acceptor impurities in semi-insulating GaAs/PBN substrates is estimated to be 1 × 10 16 cm −3 or less, and permits the implantation of 2 × 10 16 cm −3 channels which exhibit mobilities of 5,700 and 12,000 cm 2/V sec at 298K and 77K, respectively. Discrete power FET's which exhibit 0.7 watts/mm output and 8 dB associated gain at 8 GHz have been fabricated using these directly implanted semi-insulating GaAs substrates.

High-purity semi-insulating GaAs material for monolithic microwave integrated circuits

Liquid-Encapsulated Czochralski (LEC) growth of large-diameter bulk GaAs crystals from pyrolytic boron nitride (PBN) crucibles has been shown to yield high crystal purity, stable high resistivities, and predictable direct ion-implantation characteristics. Undoped (≲low 1014cm-3chromium) and lightly Cr-doped (low 1015cm-3range) -GaAs crystals, synthesized and pulled from PBN crucibles contain residual shallow donor impurities typically in the mid 1014cm-3, exhibit bulk resistivities above 107Ω . cm, and maintain the high sheet resistances required for IC fabrication (>106Ω/□) after implantation anneal. Direct29Si channel implants exhibit uniform (± 5 percent) and predictable LSS profiles, high donor activation (75 percent), and 4800- to 5000-cm2/V . s mobility at the (1 to 1.5) × 1017cm-3peak doping utilized for power FET's. It has also been established that LEC crystals can provide the large-area, round

Monolithic microwave amplifiers formed by ion implantation into LEC gallium arsenide substrates

A fabrication procedure for broad-band monolithic power GaAs integrated circuits has been demonstrated which includes formation of via holes through the 100-µm-thick GaAs substrate. A selective implant of29Si ions into the GaAs substrate is used to dope the FET channel region to 1.2 × 1017cm-3. The ohmic contacts are AuGe/Ni/Pt and the gates are Ti/Pt/Au. A 1.5-µm-thick circuit pattern is achieved using metal rejection assited by chlorobenzene treatment of AZ1350J photoresist. Using undoped Czochralski wafers of GaAs pulled from a pyrolytic boron nitride crucible, integrated amplifiers have been produced which deliver 28 ± 0.7 dBm from 5.7 to 11 GHz. These chips are 2 mm × 4.75 mm × 0.1 mm thick.

Incorporation of boron during the growth of GaAs single crystals

A study of GaAs prepared by conventional Bridgman techniques and by liquid-encapsulated Czochralski methods reveals that only small amounts of boron are incorporated from the boric oxide encapsulant. When a pyrolytic boron nitride crucible is used, there is a 100-fold increase in the amount of incorporated boron, suggesting some decomposition of the boron nitride.

The growth of single crystal lithium-aluminum, 7LiAl

Single crystal lithium-aluminum has been prepared as chemically and isotopically pure 7LiAl. Growth has been by the Stockbarger technique in a low-pressure bomb. Pyrolytic boron nitride crucibles have proven to be nonreactive and noncontaminating containers for pyrometallurgial synthesis and for crystal growth from the melt. The chemical and physical quality of the monocrystalline boules have been documented. The lattice constant varies with composition across the β-phase and can be used as a probe to evaluate stoichiometry and phase homogeneity.

Permeability, magnetomechanical coupling and magnetostriction in grain-oriented rare earth–iron alloys

Grain-oriented samples of highly magnetostrictive rare earth–iron compounds have been prepared. These samples possess lower inhomogeneous strains than found in the random polycrystalline RFe2 compounds, resulting in much higher values of relative permeability (μr) and magnetomechanical coupling (k33). A partially oriented Th.20Dy.22Ho.58Fe1.95 sample was prepared using a pyrolytic Bridgman type boron nitride crucible. At a bias field of 100 Oe k33=.73, which is considerably larger than found in the random polycrystal of the same composition. A relative permeability of 36 occurs in this same sample when a low ac drive of 1.6 Oe rms is used. A second fabrication method using a horizontal zone technique with a supporting ’’cold finger’’ was employed to grow the ternary Tb.27 Dy.73Fe1.98. The low ac drive values of k33 and μr were .74 and 19 respectively. The permeability at low bias was found to possess a sharp ac drive dependence. Near zero bias, when the drive was changed from 1.6 Oe rms to 13 Oe rms, μr in the quaternary increased from 36 to 98. In the ternary the values of μr near zero bias increased from 19 to 61. Magnetostriction measurements on both samples show a significant increase in dλ/dH and λs over the random polycrystals.

The electrical properties of undoped and oxygendoped GaP grown by the liquid encapsulation technique

Hall coefficient and conductivity measurements have been made on undoped and oxygen-doped gallium phosphide grown by the liquid encapsulation technique over the temperature range 80 to 400 K. The electrically active impurity in undoped crystals grown from a silica crucible is silicon. The thermal ionization energy of this donor is estimated at 82 meV, which is in good agreement with the optically estimated value. The ionization energy decreases with donor concentration and, to a first approximation, is given (in eV) by ED = 0·082 - 0·021 × 10−6 NDfraction one-third where ND is the donor concentration (cm−3).Undoped crystals grown from a boron nitride crucible and oxygen-doped crystals grown from a silica crucible have similar electrical properties. The room-temperature carrier concentration in these crystals lies between 5 × 109 and 2 × 1015 electrons/cm3 and the thermal ionization energies range from 0·20 to 0·55 eV. The impurities responsible for these levels have not been identified although it seems likely that oxygen is involved.

The localized vibrations of nitrogen in gallium phosphide

Infrared absorption measurements on gallium phosphide crystals grown in a boron nitride crucible have revealed a localized vibrational mode at 496.1 +or- 0.2 cm-1. Absorption measurements made on these samples in the visible part of the spectrum showed that nitrogen was present and the vibrational mode is therefore attributed to this impurity.

Transport numbers in molten fluorides—I. Sodium fluoride

The external transport number of Na + in molten NaF was determined to be 0·64 ± 0·05 by a tracer technique. A boron-nitride crucible was used as reference; it also served as a diaphragm separating the anolyte and the catholyte. Viscous flow could not be avoided completely, but was corrected for by performing several experiments and extrapolating to zero charge.

Evaluation of Pyrolytic Boron Nitride Crucible Thimble in Carrier Gas Fusion Determinations of Gases in Metals.

Evaluation of Pyrolytic Boron Nitride Crucible Thimble in Carrier Gas Fusion Determinations of Gases in Metals.

New Pair Spectra in Gallium Phosphide

Crystals of GaP doped with Zn+Te, Zn+Se, Cd+Te, and Cd+Se were grown from gallium-rich solutions contained in pyrolytic boron nitride crucibles, using vapor-grown GaP as source material. The low-temperature photoluminescence of these crystals reveals the presence of new pair spectra involving zinc or cadmium on gallium sites and tellurium or selenium on phosphorus sites (type II spectra). The values of (${E}_{A}+{E}_{D}$), the sum of the acceptor and donor binding energies, derived from the spectra are in excellent agreement with the values predicted from previously observed pair spectra. The data on all the previously observed spectra have also been recalculated to yield more consistent values of (${E}_{A}+{E}_{D}$) and the Van der Waals parameter.

Sc5Ga3and Y5Ga3withD88structure

Abstract : The phases Sc5Ga3 and Y5Ga3 were synthesized in an investigation of the occurrence of compounds with D8 sub 8 structure. Induction melting of the metals mixed in proper weight proportions in a boron nitride crucible under argon produced homogeneous samples of Se5Ga3 and Y5Ga3. (Author)