Liquid Encapsulation Technique Research Articles

Synthesis and crystallization of ZnSe by the liquid encapsulation technique

In this paper we present the preliminary results of ZnSe crystal growth by liquid encapsulated Czochralski (LEC) technique. The influence of thermal conditions on the crystal growth process and the properties of the boules were studied. Investigation of physical parameters (resistivity measurements, photoluminescence, infrared transmission) showed the high purity of the obtained material and indicated that the LEC technique can be used for obtaining large single crystals of ZnSe.

Plasticity of undoped GaAs deformed under liquid encapsulation

Undoped GaAs single crystals with 〈123〉 orientation are compressed at different strain rates in the temperature range between 730 and 900 °C, using the liquid encapsulation technique to prevent As loss. The resulting stress-strain curves are characterized by five deformation stages, as is known for other semiconductors. From the lower yield point, at high strain rates, an activation energy of 1.37 eV and a stress exponent of 3.6 are deduced; these parameters nearly agree with those obtained earlier at lower temperatures and under a protective atmosphere of argon. At low strain rates deviations occur, whose origin is discussed. The analysis of the first stage of dynamical recovery (stage III), which shows a uniform behavior over the whole temperature and strain-rate range, yields an activation energy of 2.3 eV and a stress exponent of 4.2. These values are discussed in terms of a diffusion-controlled recovery mechanism. The second recovery stage (stage V) probably is governed by cross slip; the cross over of both recovery regimes takes place near 550 °C. The deformation behavior of GaAs is compared to that observed in other semiconductors.

X-ray investigation of crystal defects in Czochralski grown InP single crystals

X-ray diffraction topography was employed to study extended crystal defects in InP single crystals grown by the Czochralski liquid-encapsulation technique. Semi-insulating iron-doped, p-type and n-type crystals were investigated and two main defects, dislocation lines and large precipitate-like defects, were evidenced. The generation mechanism for the dislocations and the nature of the large defects were analyzed.

Use of implanted samples as standards in spark-source mass spectrometry with application to the analysis of III—V semiconductors

Summary The method described for the analysis of III—V semiconducting materials by sparksource mass spectrometry is especially suitable for the characterization of indium phosphide single crystals. As a means of standardization, some of the crystals were doped either uniformly during growth or by implantation of a well-defined dopant at levels of 1014–1015 atoms cm-2. Implantation is shown to be valuable for providing standards at low levels of impurities. The main impurities in indium phosphide single crystals are Si, C, O, B, N, Al, (S), Zn and As, but sixteen other elements are present below the detection limit. In a single crystal grown by the liquid encapsulation technique, two types of impurity segregation, along the axis of growth and along the radial axis, are revealed.

The growth and perfection of single crystal indium phosphide produced by the LEC technique

This paper describes recent studies at RSRE concerned with identifying residual impurities and structural defects in single crystal InP grown by the Czochralski liquid encapsulation technique (LEC) and discusses means whereby the impurities and defects can be controlled. The role of some deliberately added dopants (e.g., Fe, Co and Ge) in inducing specific properties is also described.

Dislocation clusters in Czochralski-grown single crystal indium phosphide

Clusters of etch pits which sometimes form in single crystal indium phosphide grown by the Czochralski liquid-encapsulation technique, are shown to equate with prismatic dislocation loops generated by a stress source at the centre of the cluster. The morphology of the clusters and the conditions under which such clusters form are shown to be consistent with the presence of either a precipitate or an inclusion. It is demonstrated that water vapour associated with the boric oxide used as the liquid encapsulant is a positive cause of clusters and that vacuum baking is a pre-requisite for their control. The elements responsible for the stress generation promoting the clusters have not been positively identified but the likely possibilities are discussed.

Etch features in Czochralski-grown single crystal indium phosphide

Two etchants for InP have been used to categorize etch features in both horizontal and vertical sections of InP single crystals grown by the Czochralski liquid encapsulation technique; these are the AB etchant, used extensively for defect analysis in GaAs and another etchant based on a phosphoric acid/hydrobromic acid mixture. The behaviour of these etchants is different but a cross correlation has been made between the types of etch feature produced. Transmission X-ray topography has been used to correlate etch features with dislocations. Nominally undoped crystals and material doped with specific impurities, e.g. Fe, Ge, Zn, have been examined. The principal features produced by etching are pits, ridges and striations. It is shown that the density and distribution of pits and ridges is consistent with these features being dislocation structures and the mechanisms by which they are revealed are discussed in terms of etching rates. The results allow comment to be made upon interface shape and the source of dislocations in InP crystals grown by the Czochralski technique.

The electrical properties of n-type semi-insulating indium phosphide

The electrical properties of semi-insulating n-type indium phosphide single crystals which have been pulled from the melt by the liquid-encapsulation technique are reported. Measurements of thermal activation energies for both ohmic and space-charge limited conduction over a broad temperature range have enabled the deduction of both depth and concentration of the localized levels in Cr-doped material. One dominant level is situated approximately 0.20 eV from the conduction band. A deeper level at 0.54 eV is attributed to the Cr impurity in the crystals. Data for iron-doped InP show that this type of crystal may also be suitable as an epitaxial substrate material.

Impurity effect on the growth of dislocation-free InP single crystals

Dislocation-free InP crystals were pulled in a 〈111〉 %In direction by using a liquid encapsulation technique. InP crystals were free from dislocations only when they were grown from a melt doped heavily with impurities. Zn was found to be the most effective impurity to reduce the grown-in dislocation. Dislocation density was drastically decreased when Zn concentration exceeded a value of 1018/cm3. Donor impurities, such as S and Te, were also effective in reducing the grown-in dislocation. A single-bond energy model for the impurity effect on reduction of dislocations is proposed. Zn and S were presumed to also be effective in making dislocation-free GaAs, in light of this model. These were confirmed by experiment.

不純物添加によるＩＩＩ‐Ｖ族化合物の無転位結晶成長

Dislocation-free InP and GaAs crystals have been grown by a liquid encapsulationtechnique by means of an impurity doping procedure. It was found that grown-indislocations were diminished, when a certain kind of impurities was added into themelt from which crystal was pulled.Impurity effect on grown-in dislocation density was examined for Zn, S and Te inInP, and for Zn, S, Te, Al and N in GaAs. It was found that these impurities wereeffective for reducing grown-in dislocation density, except for Zn in GaAs.Effectiveness of impurity for reducing the grown-in dislocation density was ascribedto strength of bonds formed between the substitutional impurity atoms and host crystalatoms surrounding the impurity atoms.

High pressure Czochralski growth of Fe 1−xS (0< x≤0.1) single crystals

The high-pressure Czochralski growth of Fe 1− x S crystals (0< x≤0.1) is described. As x approaches zero (troilite) the low equilibrium vapour pressure of sulphur permits direct pulling under an argon pressure of 20 atm. The occurence of defects such as cells and Fe/FeS eutectic structures are related to the incongruent melting of such crystals; the occurence of cracking is related to the anisotropic thermal expansion which has been measured by X-ray diffraction at temperatures in the range 20–500°C. Congruently melting crystals ( x≅0.1) have been grown using the high-pressure B 2O 3 liquid encapsulation technique to prevent sulphur vapour loss (equilibrium vapour pressure of sulphur ca. 1 atm). Although B 2O 3 does not wet the growing crystal, growth at the congruent melting composition offers advantages with respect to the occurence of defects such as cellular structures, oxide inclusions and cracking.

Eutectic formation in chromium-doped indium phosphide

The occurence of second phase separation in chromium-doped indium phosphide is reported. The phenomenon has been studied in crystals grown by the high pressure. Liquid Encapsulation Technique. The second phase was examined by infra-red microscopy, X-ray microanalysis and scanning electron microscopy. X-ray diffraction patterns of the second phase were obtained after the host material had been chemically removed. On this evidence the second phase has been identified as eutectic needles of chromium phosphide (CrP). The needles showed a high degree of short range order and a general alignment almost parallel to the growth axis.

Dislocation-free GaAs by the liquid encapsulation technique

Dislocation-free GaAs single crystals were grown by the liquid encapsulation technique by means of a necking-in procedure. It was found that the thinning of the crystal diameter is the main step for diminishing the dislocations. The stoichiometry of the melt composition is not very critical; it can be sufficiently maintained with regard to an adapted growing rate. A low temperature gradient near the solid-liquid interface is necessary and can be governed by the encapsulating B2O3 itself. No dislocations must be created by the B2O3 melt. Crystals were grown in [111]-as well as in [100]-orientation. The dislocations were examined by etching the (111)-Ga surface and (100) surface, respectively. It was found that all dislocations of the seed crystal have disappeared from the neck portion toward the crystal surface.

Crystal growth and properties of group IV doped indium phosphide

InP crystals have been grown from the melt by the high pressure liquid encapsulation technique. A study of the segregation of group IV elements based on measurements of free electron concentrations in doped crystals indicates that the mean effective distribution coefficients for Ge and Sn are 2.4 × 10−2 and 2.1 × 0−2 respectively. Whereas doping with Ge and Sn gave high quality and reproducible n-type crystals, controlled doping experiments using Si and Pb were not successful. The role of these latter elements together with that of C is discussed. The characteristic photoluminescence spectra of these doped crystals were measured at 77°K, and in conjunction with the electrical and chemical evidence thepeaks were assigned to specific impurity/vacancy interactions. The highest energy peak at about 1.41 eV is associated with donors and is sensitive to Ge and Sn doping, while the acceptor level appears to lie at 1.37 eV. The peaks at 1.32 eV and 1.35 eV are attributed to the effects of growth from B2O3 and copper doping respectively, and the broad peak between 1.12 and 1.20 eV may be associated with phosphorus vacancies.

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.

Preparation and Properties of Bulk In1 − xGaxAs Alloys

Single crystals of have been grown by Czochralski techniques for and . Polycrystalline single‐phase material has also been pulled for . Two Czochralski techniques were employed: (i) the sealed system or Gremmelmaier technique, and (ii) the liquid encapsulation technique. Mass spectrographic data have been correlated with alloy lattice parameter determinations on the as‐grown material to yield information on the solidus curve of the system. Hall measurements were made and impurity analyses were performed using the spark source mass spectrometer.

The absorption coefficient of gallium phosphide in the wavelength region 530 to 1100 nm

The absorption coefficient of gallium phosphide has been measured over the spectral width of a red light emitting diode. The material was grown by the liquid encapsulation technique, and an absorption associated with the presence of oxygen has been observed.

Nachweis und diffusion von Sauerstoff in GaAs

The oxygen content of GaAs single crystals grown under a protective B 2O 3 melt by the liquid encapsulation technique was determined by mass spectrometry, deuteron and neutron activation analysis and was found to be 10 19 –10 20 atoms cm -3. Crystals grown from the melt by other techniques as well as vapour- and solution-grown epitaxial layers were found to have concentrations of the same order of magnitude. An estimate from mass-spectrometric data yields an effective diffusion coefficient of oxygen in GaAs of D eff = 2 × 10 -3 exp (-1.1 eV.kT) cm 2 s -1 between 700 and 900°C.

On the preparation and electrical properties of PtSb2

The preparation and the Czochralski growth of single crystals of PtSb2 by a liquid encapsulation technique is described. Conductivity and Hall effect measurements have been made in the temperature range 20 to 300° K. It is found that the material is n-type, with a carrier concentration of about 6 × 1016/cm3, the ratio of electron to hole mobility,μe/μh, is 0.57 at 110° K, and the electron mobility has a maximum value of 2100 cm2/V sec at 50° K. The thermal energy gap is 0.112 eV.

Crystal pulling and constitution in Pb1?xSnxTe

Single crystals of Pb1−x Sn x Te have been pulled from the melt using the liquid encapsulation technique and the onset of constitutional supercooling as a function of growth rate has been investigated. From the analysis of crystals and their corresponding melts, a drastically revised phase diagram of the PbTe/SnTe pseudo-binary system has been constructed.