Liquid Encapsulated Czochralski Technique Research Articles

Distribution of Carbon in Large Diameter Semi-Insulating Gallium Arsenide Grown by Liquid Encapsulated Czochralski Technique

Carbon impurity concentration and dislocation density were investigated with optical microscopy and Fourier transform infrared absorption spectrometer in radial direction of large diameter (6-inch) undoped semi-insulating Gallium Arsenide (SI-GaAs) grown by liquid encapsulated Czochralski (LEC). The experimental results showed that their distributions are both “W”-shaped along wafer diameter, which is relatively higher on the center and lower near the center, but highest on the edge of the wafer. The nonuniformity distribution of thermal stress from growth process leads to the “W”-shaped distribution of dislocations in radial direction. The adsorption of matrix elastic strain field around dislocations induces the “W”-shaped distribution of carbon impurity. Dislocations adsorb carbon impurity and carbon impurity decorates dislocations. Dislocation density distribution affects carbon behavior.

The Dislocation Density Distribution of Different Types of Doped InP Wafers

It is of great significance to study on the dislocation density distribution of different types of doped indium phosphide (InP) crystal wafers for fabricating high-quality InP single crystal with low dislocation density. In the paper, a new etched pits density mapping (EPD mapping) measurement is introduced to measure the dislocation density distribution of the S-doped, Fe-doped and non-doped InP wafers pulled by high-pressure liquid encapsulated Czochralski (HP-LEC) technique. Test results show that in the three types of InP wafers， the S-doped InP wafer’s dislocation density is lowest and uniformity is best; the non-doped InP wafer’s dislocation density is maximum and uniformity is the worst; the Fe-doped InP wafer’s dislocation density and uniformity are between the S-doped and non-doped InP wafers. In the paper, the measurement results are analyzed in detail also from the faces of the doping and crystal growth process and thermodynamic mechanism. This study shows that in addition to traditional methods, using reasonable doping process can also effectively reduce the dislocation in the crystal, enhance the lattice strength and improve the uniformity of the InP single crystal.

Influence of Silicon and Boron Doping on the Thermal Conductivity of N-GaAs Single Crystals

Thermal conductivity of three different GaAs crystals, one grown by Liquid Encapsulated Czochralski technique and the other two samples grown by Vertical Bridgman technique have been experimentally measured at temperatures 310 K to 360 K. Two crystals are undoped and semi insulating and one crystal is conductive which is doped with Si and B(Silicon ≈ 4x1015 cm-3 and Boron ≈ 8x 1015cm-3). It has been experimentally observed that doping of silicon and boron gives rise to an increase in thermal conductivity.

Room temperature particle detectors based on indium phosphide

A study of electrical properties and detection performance of particle detectors based on bulk InP and semiconducting LPE layers operated at room temperature is presented. Bulk detectors were fabricated on semi-insulating InP crystals grown by liquid-encapsulated Czochralski (LEC) technique. High purity InP layers of both n- and p-type conductivity were used to fabricate detector structures with p–n junction. The detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from 241Am source at room temperature. Better noise properties were achieved for detectors with p–n junctions due to better quality contacts on p-type layers.

Room-temperature particle detectors with guard rings based on semi-insulating InP co-doped with Ti and Zn

Particle detectors made with a guard-ring (GR) electrode, operating at room temperature, have been studied. The detectors were fabricated on a semi-insulating InP crystal co-doped with Ti and Zn, grown using the Liquid-Encapsulated Czochralski technique. The detection performance of the particle detectors was evaluated using alpha particles emitted from a 241Am source. Good detector performance has been achieved with measured charge-collection efficiencies of 99.9% and 98.2% and FWHM energy resolutions of 0.9% and 2.1%. The measurements were carried out at 230 K for negative and positive bias voltages of the irradiated electrode. The good performance is due to the SI properties of the material which has been achieved by doping with suitable Ti atoms and co-doping with a low concentration of Zn acceptors, sufficient to fully compensate shallow donors. Electron and hole charge-collection efficiencies (CCEs) were measured at various temperatures. At room temperature, unlike at low temperature ( T<250 K), the hole CCE was better than the electron CCE, which can be explained by the presence of electron-trapping centres in InP with a temperature-dependent capture rate.

Analysis of twin formation in sphalerite-type compound semiconductors: A model study on bulk InP using statistical methods

The type of twinning in sphalerite-type III–V compound semiconductors is well known. However, the detailed formation mechanism, although intensively studied in the last two decades, is not entirely understood. It is still widely accepted that twin formation is a rather fortuitous issue. In addition to many empirical observations and phenomenological explanations, there was a first theoretical approach by Hurle [Speculation Concerning the Causes of Twinning during Czochralski growth of Crystals having Diamond Cubic or Zinc-blende Structure, 1991], later refined. The theory predicts a correlation between crystal slope angle α and twin generation frequency, where α is defined as the angle between the tangent to the crystal surface and the growth axis. Angles of 70 . 53 ∘ and 74 . 21 ∘ should promote twinning, while that of 35 . 26 ∘ should reduce twin frequency. However, a critical review of experimental results on InP, grown by LEC (liquid encapsulated Czochralski) and VCz (vapor pressure controlled Czochralski) techniques, does not yield such a clear correlation. To shed some more light on the possible factors already discussed in literature, a systematic study based on statistical methods is performed. It can be shown that, at least for the Czochralski technique, twin formation is closely connected to the crystal growth rate and its fluctuations, i.e. instabilities of the growth system. This confirms some of the literature suggestions.

X-Ray High-Resolution Diffraction and Transmission Topography Study of InGaAs Grown by Liquid Encapsulated Czochralski Technique

Laser diodes, solar cells, photodetector structures and other optoelectronic applications of InGaAs ternary bulk crystals and layers stimulate constant interest in the improvement of growth methods for this material. Growth of bulk ternary crystals based on III–V compounds with chemical compositions given by formula A 1−xB III x C V is a difficult task due to the thermodynamical properties of their solutions. Most of the techniques to obtain ternary crystals are focused on layer growing on the relevant substrates. Techniques like metalorganic chemical vapor deposition (MOCVD) [1, 2], metalorganic vapor phase epitaxy (MOVPE) [3, 4] and molecular beam epitaxy (MBE) [5, 6] are often used. Growth of quantum wells and quantum wires is also focused on ternary crystals. Some theoretical discussions about bulk growth of ternaries can be found in [7]. Recently rotational Bridgman method [8], liquid phase electroepitaxy [9] and zone growth [10] were used. ∗corresponding author; e-mail: Jerzy.Gronkowski@fuw.edu.pl

Direct recognition of non-radiative recombination centers in semi-insulating LEC InP:Fe using double excitation photoluminescence

In order to observe the effect of intra-band gap excitation on the photoluminescence (PL) properties of undoped InP and iron doped InP (InP:Fe), PL measurements were performed in InP crystals with thickness of 360 μm and area of about 4×3 mm 2, grown by the liquid encapsulated Czochralski (LEC) technique upon excitation with both Ar-ion laser and 980 nm light. The PL intensities for InP:Fe under 980 nm wavelength light illumination relative to no illumination increased by about 52%, 33%, and 12% for the 1.337, 1.380, and 1.416 eV peaks, respectively, at 10 K, whereas there was no illumination effect for undoped InP. This is a strong indication that Fe centers play a role as non-radiative recombination centers to decrease the PL intensity. PL experiments were performed in the spectral range of 1320–1440 meV for InP in the sample temperature range of 10–160 K. The electron and hole photoionization cross-sections at 980 nm wavelength light illumination were calculated as σ n 0 [ Fe 2 + / 3 + → CB ] = 2.34 × 1 0 - 18 cm - 2 and σ p o [ VB → Fe 2 + / 3 + ] = 8.20 × 1 0 - 17 cm 2 , respectively.

Temperature-Dependent Galvanomagnetic Measurements on DopedInSb and InAs Grown by Liquid Encapsulated Czochralski

Resistivity, magnetoresistivity and Hall effect measurements in n-typeTe-doped InSb and S-doped InAs samples grown by the liquid encapsulatedCzochralski technique were carried out as a function oftemperature (14–350 K) and magnetic field (0–1.35 T). In Te-dopedInSb, an impurity level with energy E1 = 3 meV andthe activation energy E0 = 0.26 eV, which is the band gapenergy, are obtained from the resistivity and Hall carrierconcentration analysis. In S-doped InAs, both the linear and power lawmodels are used in explaining the temperature-dependent resistivity.The effects of impurities on the electron and magnetic transportationproperties of InAs and InSb have also been discussed.

2D simulation of carbon transport at the growth of GaAS crystals by liquid encapsulated Czochralski techniques

We present a 2D model for the unsteady carbon transport and incorporation into the crystal during the vapor pressure-controlled Czochralski growth of semi-insulating GaAs. The model is based on a conjugated analysis of global heat transfer, turbulent melt convection, and the flow in the encapsulant within a quasi steady-state approximation. Carbon transport in the melt is coupled to the transport of carbon monoxide in B 2O 3 encapsulant, assuming CO dissolution at the melt/encapsulant interface. CO concentration in the gas near the encapsulant surface, estimated from experimental observations, is used to formulate an external boundary condition. The model is validated using measurements of carbon concentration in grown 3-in GaAs crystals. The results obtained help to reveal basic mechanisms controlling carbon incorporation into the crystal.

Comparative study on residual strain and thermal stress in 4-in GaAs crystals grown by LEC and VB techniques

Residual strains of 4-in diameter GaAs crystals grown by liquid encapsulated Czochralski (LEC) and vertical Bridgman (VB) techniques have been measured by scanning infrared polariscope (SIRP). It was found that the residual strain of the substrate cut at the shoulder portion of a LEC-grown crystal was remarkably larger than that cut at the middle portion of the crystal. It was also found that the residual strains of the substrates cut at the shoulder and middle portions of a VB-grown crystal were both smaller than those of the LEC-grown crystal, and showed the similar values and profiles with each other. Von Mises stress and excess shear stress according to the Jordan's criterion were calculated to understand these experimental results. It was found that large thermal stress was caused during the LEC growth especially in the early stage, while thermal stresses caused during the VB growth were considerably smaller than those caused during the LEC growth from the shoulder to the middle. These experimental and analytical results suggest that the difference in the residual strain along the growth axis between LEC and VB crystals is due to the difference of the thermal stress caused during the crystal growth between LEC and VB techniques.

Growth of co-doped semi-insulating indium phosphide crystals for X-ray detection

Co-doped indium phosphide crystals were grown by liquid encapsulated Czochralski technique for application in X-ray detection. Semi-insulating state was created by iron–zinc, titanium–zinc and titanium–manganese co-doping using one or two stage growth procedure. Crystals were characterized by temperature-dependent resistivity and Hall coefficient measurements. The resistivity of InP(Fe,Zn) was 5.8×10 7 Ω cm, of InP(Ti,Zn) was 3.7×10 5 Ω cm and of InP(Ti,Mn) was 2.2×10 6 Ω cm.

Evidence of a sulfur-boron-hydrogen complex in GaAs grown by the liquid encapsulation Czochralski technique

In LEC-grown GaAs:S, two vibrational absorption lines are measured at 2382.2 and $2392.8\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $(T=7\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and assigned to $^{11}\mathrm{B}\ensuremath{-}\mathrm{H}$ and $^{10}\mathrm{B}\ensuremath{-}\mathrm{H}$ stretching modes. Uniaxial stress experiments reveal that the symmetry of the responsible complex is ${C}_{s}$. Bond strength considerations suggest that this complex is a ${\mathrm{S}}_{\mathrm{As}}\ensuremath{-}{\mathrm{B}}_{\mathrm{Ga}}$ pair passivated by hydrogen bonded to boron. The constituents of this $\mathrm{S}\ensuremath{-}\mathrm{B}\ensuremath{-}\mathrm{H}$ complex are located within a {110} plane.

Comparative study on residual strain profiles in GaAs substrates grown by LEC and VB techniques

Residual strain profiles have been experimentally and theoretically compared between the two different growth techniques preparing GaAs substrates. One is the vertical boat (VB) technique and the other is the liquid-encapsulated Czochralski technique. It is found from the experimental observations that the residual strain profile of VB substrate is simple bowl-shaped, in which the residual strain value is high near the peripheral region, while the residual strain profile of LEC substrate is more complex and fourfold-symmetrical, in which the residual strain value is high in the inner regions as well as near the peripheral regions. In order to explain this experimental observation, we have estimated the thermal stress caused during the crystal growth by computer analysis. Thermal stress during VB growth is dominantly caused near the solid-liquid interface. On the other hand, strong thermal stress is caused during LEC growth both near the surface of boric oxide encapsulant and near the solid-liquid interface. It is therefore concluded that the observed difference of residual strain profiles may be coming mainly from the temperature profile difference between VB and LEC techniques.

Electrical properties of semi-insulating GaAs crystals grown by vertical gradient freeze and liquid encapsulated Czochralski techniques

Electrical, photoelectrical, luminescent characteristics and the spectra of deep levels are compared for undoped semi-insulating SI-GaAs crystals grown by vertical gradient freeze (VGF) and liquid encapsulated Czochralski (LEC) techniques. It is shown that generally the reverse current of the Schottky diodes prepared on VGF material is considerably lower than for the LEC material which could be a serious advantage for use in radiation detectors. At the same time it is demonstrated that such parameters as photosensitivity and bandedge luminescence efficiency are to a greater extent dependent on the type of the ingots annealing procedure setting up the deep levels spectra in the material than on dislocation density.

Preliminary study of two immiscible liquid layers subjected to a horizontal temperature gradient

Marangoni convection, driven by interfacial instability due to a surface tension gradient, presents a significant problem in the crystal growth process. To achieve better materials processing, it is necessary to suppress and control this convection, especially in crystal growth using Liquid Encapsulated Czochralski techniques in which the melt is encapsulated in an immiscible medium. Marangoni convection can occur at the liquid-liquid interface and at the gas-liquid free surface. Buoyancy driven convection can also affect and complicate the flow. The present report studied Marangoni convection in a two-liquid layer system in an open and enclosed cavity. Flow in the cavity was subjected to a horizontal temperature gradient. Interactive flow near the liquid-liquid interface was measured by the Particle Image Velocimetry (PIV) technique. The measured flow field is in good agreement with numerical predictions.

Synchrotron X-ray topography of electronic materials.

Large-area transmission, transmission section, large-area back-reflection, back-reflection section and grazing-incidence topography are the geometries used when recording high-resolution X-ray diffraction images with synchrotron radiation from a bending magnet, a wiggler or an undulator of an electron or a positron storage ring. Defect contrast can be kinematical, dynamical or orientational even in the topographs recorded on the same film at the same time. In this review article limited to static topography experiments, examples of defect studies on electronic materials cover the range from voids and precipitates in almost perfect float-zone and Czochralski silicon, dislocations in gallium arsenide grown by the liquid-encapsulated Czochralski technique, the vapour-pressure controlled Czochralski technique and the vertical-gradient freeze technique, stacking faults and micropipes in silicon carbide to misfit dislocations in epitaxic heterostructures. It is shown how synchrotron X-ray topographs of epitaxic laterally overgrown gallium arsenide layer structures are successfully explained by orientational contrast.

Investigation of semi-insulating oxygen-doped GaAs

We found Oxygen-doped GaAs crystals to be suitable materials for CO 2 laser optical component preparation, with application at 10.6 μm. An optical transmission of 55% in the IR spectrum range, between 2 and 15 μm has been reached for such a GaAs type material. The GaAs crystals that we have analysed were grown by two procedures: Horizontal Bridgman (HB) and Liquid Encapsulated Czochralski (LEC). The HB method has been used for obtaining pure (undoped) crystals, while the oxygen-doped GaAs ingots were grown by LEC technique. The two types of samples processed in the same manner as regards mechanical polishing and chemical etching, which were investigated by Hall measurements, optical transmission spectrometry and elastic recoil detection analysis (ERDA) technique. The GaAs:O (LEC) has near semi-insulating properties as can be observed from the results of the electrical resistivity and Hall effect measurements. The ERDA spectrum shows an intense signal of oxygen in the bulk of GaAs:O (LEC) crystals, while the oxygen signal is not present in the ERDA spectrum of the undoped GaAs (HB). We consider that these results could recommend the ERDA technique as a possible qualitative and quantitative analysis in an ion-beam accelerator for oxygen content in oxygen-doped GaAs crystals. The analysis is not sensitive to the native oxide, as could be seen by measuring GaAs (HB) undoped crystals.

Investigation by γ-ray diffraction of the crystalline quality of GaAs and InP single crystals

The crystalline quality of GaAs and InP single crystals grown by the liquid-encapsulated Czochralski technique, was investigated by γ-ray diffraction. In particular, the rocking curve was measured in different areas of each crystal, obtaining the mosaic spread, which characterises the grain disorientation around the average direction. The analytical technique which was used, proved useful for the non-destructive characterisation of nearly perfect crystals. In particular, the crystalline quality of Si-doped GaAs and S-doped InP single crystals was found to be very high, whereas the undoped InP crystal appeared to be of worst quality, with a mosaic of the order of few minutes and varying from place to place.

Vibrational Absorption of a Nitrogen–Oxygen Complex in GaP

In liquid encapsulated Czochralski (LEC) grown GaP, a set of twelve vibrational absorption lines is measured in the frequency region 500 to 1150 cm -1 . They originate from a single defect as their intensities are correlated with each other. It is shown that this defect is a [N-O] complex consisting of several nitrogen and oxygen atoms. This complex is characteristic of GaP produced with the LEC technique under high nitrogen inert gas pressure conditions.