Liquid Encapsulated Czochralski Method Research Articles

Impurities related micro-defects in GaSb crystal grown by LEC method

The epitaxial growth of devices based on gallium antimonide (GaSb) is negatively impacted by defects related to impurities in the crystal. Liquid encapsulated czochralski (LEC) technology was used to grow 2-inch Te-doped GaSb (100) single crystal ingots, which were then processed into polished wafers in order to investigate the origins and consequences of defects related to impurities. Polished GaSb wafers were found to have surface micro-defects. Energy dispersive x-ray spectroscopy (EDAX) and scanning electron microscopy (SEM) measurements indicate that the micro-defects are associated with carbon and oxygen impurities. Glow discharge mass spectrometry (GDMS) is used to identify the origins of carbon and oxygen impurities. Based on the findings, an optimization process was developed to enhance the crystal quality, and a micro-defect-free GaSb single crystal was produced.

Phosphorus escaping phenomena during the growth of InP crystal by in-situ liquid-encapsulated Czochralski method and P-rich-related defects in InP crystal

Phosphorus escaping phenomena during the growth of InP crystal by in-situ liquid-encapsulated Czochralski method and P-rich-related defects in InP crystal

Численное моделирование процесса выращивания монокристаллов методом Чохральского в квазистационарном приближении

We consider the steady-state growth of a single crystal by the liquid encapsulated Czochralski method. The mathematical model accounts for heat transfer in the crystal, melt and encapsulant, radiative heat exchange between the crucible and the surrounding furnace, formation of the growth interface and the melt/encapsulant interface meniscus, release of the latent heat during the phase transition. The time history of the growth is reconstructed from a sequence of steady state calculations with decreasing melt depth. The numerical method is based on explicit interface tracking. The employed computational procedure ensures global conservation of thermal energy. The response of prototype growth system for changes in pull rate or heater temperature is examined numerically.

Stability Analysis of Thermocapillary Convection of B<sub>2</sub>O<sub>3</sub>/Sapphire Melt in an Annular Pool

Aiming at the thermocapillary convection stability of sapphire crystal grown by liquid-encapsulated Czochralski method, by non-linear numerical simulation, obtained the flow function and temperature distribution of R-Z cross section, as well as the velocity and temperature distribution at liquid-liquid interface and monitoring point of B2O3/sapphire melt in annular two liquid system, covered with solid upper wall and in microgravity. By means of linear stability analysis, obtained the neutral stability curve and critical stability parameters of the system, and revealed the temperature fluctuation of the liquid-liquid interface. The calculated results of B2O3/sapphire melt were compared with 5cSt silicone oil/HT-70. The results show that under the same geometrical conditions, the flow of B2O3/sapphire melt system is more unstable than 5cSt silicone oil/HT-70, there are two unstable flow patterns, radial three-dimensional steady flow cell and hydrothermal waves near the hot wall. The larger the ratio of Pr number of upper and lower fluid layers is, the better the effect of restraining the flow of lower fluid layers is.

Residual stress distribution and flatness of dislocation-free Te-GaSb (100) substrate

Raman spectroscopy has been used to evaluate residual stress distribution across GaSb single crystal wafers with different Te doping concentrations grown by liquid encapsulated Czochralski (LEC) method. Undoped GaSb wafers grown by LEC and vertical temperature gradient freezing method were used as reference wafers for comparison analysis. The residual stress increases but its distribution uniformity improves in LEC-GaSb wafers with the concentration of Te dopant increasing. Moreover, annealing at temperature 650 °C can effectively increase its distribution uniformity and results in an improvement of the flatness. The results also suggest that the flatness of GaSb wafers is better when Te doping concentration is controlled within a certain range.

Evaluation of LEC and VGF-InAs substrates through surface defect characterization and epitaxy growth

Undoped InAs (100) substrate wafers prepared by liquid encapsulated Czochralski (LEC) and vertical temperature gradient freezing (VGF) methods have been studied and compared in their epi-ready state. The substrate surface defects have been analyzed by surface scanner KLA candela, Energy Dispersive X-Ray Spectroscopy (EDAX), Total-reflection X-ray fluorescence spectroscopy (TXRF), with an aim to find the contrast between LEC-InAs and VGF-InAs substrates. It is found that the VGF wafers have lower surface point defects and good stoichiometry compared with the LEC-wafer. VGF-InAs is more favorable to LEC-InAs for oxide thermal desorption and midwavelength infrared（MWIR）epitaxial layer growth with low defect density.

Investigation of thick GaAs:Cr pixel sensors for X-ray imaging applications

The new generation of synchrotron radiation sources sets advanced requirements in the performance of hybrid pixel detectors. A critical point in the design of such detectors is the choice of the sensor material. Chromium-compensated Gallium Arsenide (GaAs:Cr) is a promising candidate for use in pixel detectors, targeting imaging applications in the intermediate energy range 20–50 keV. In this work, thick GaAs:Cr sensors grown recently using the Liquid Encapsulated Czochralski (LEC) method were bonded to Timepix chips. The performance of the sensors was characterised by using various X-ray sources in view of imaging applications. The uniform illumination of the sensors reveals inhomogeneities due to the presence of crystal defects in the microscopic level. Using a micro-focused X-ray beam we extract sensitivity maps and the mobility-lifetime product at the pixel level. The results obtained confirm that the non-uniformities observed at the sensor level are directly linked with the microscopic defects. Overall, the efficient use of such sensors in X-ray imaging applications relies on their stability over irradiation-time.

Influence of melt convection on distribution of indium inclusions in liquid-encapsulated Czochralski-grown indium phosphide crystals

Indium (In) inclusions have been found in 〈100〉 indium phosphide (InP) single crystals grown in In-rich melt by the liquid-encapsulated Czochralski (LEC) method. Two kinds of In inclusions with different morphologies, one is lath-like and the other is polyhedral, have been observed. Most of the In inclusions are lath-like and their long sides are always parallel to the $$[0\overline{1}1]$$ or $$[0{\overline{1}}{\overline{1}}]$$ orientation. In (100) InP wafers, these inclusions mainly distribute in two regions viz., center of the wafer and annular belt at a certain distance from the center. These special distributions of In inclusions in InP crystals were found in our experiments for the first time. In order to clarify the cause of the special distributions of In inclusions, numerical simulations have been carried out on the melt convection in the process of InP crystal growth. The results show that the rotations of crystal and crucible significantly affect the number and direction of convection cells in the melt, which have a great influence on the enrichment and distribution of excess In at the solid–liquid interface. Different melt convections modify the radial distributions of excess In atoms near the solid–liquid interface and result in different radial distributions of In inclusions in the crystals.

Evaluation of residual stress in InP and InAs (100) substrates obtained from single crystals grown by LEC and VGF methods

Raman spectroscopy has been used to characterize and compare residual stress distribution across wafers sliced from un-doped InP and InAs single crystals grown by liquid encapsulated Czochralski (LEC) and vertical temperature gradient freezing (VGF) methods, respectively. Both VGF-InP and VGF-InAs wafers exhibit greater residual stress but even distribution across the wafer than their LEC wafers. There is an inverse distribution correlation between the residual stress and the Full width at half maximum (FWHM) of Raman peak for the wafer grown by LEC or VGF method. The flatness results suggest that VGF-grown wafers generally have better flatness parameters but with higher residual stress than LEC-grown wafers.

A Comparison of Defects Between InAs Single Crystals Grown by LEC and VGF Methods

InAs single crystals grown by the liquid-encapsulated Czochralski (LEC) method and vertical gradient freezing (VGF) are studied by low-temperature photoluminescence spectroscopy, infrared transmission and reflectance spectroscopy, double-crystal x-ray diffraction and Hall effect measurement, respectively. A properly controlled etching solution is used to reveal beautiful square dislocation etch pits in the crystals. In addition to extremely low dislocation density, the concentration of native defects in the VGF-InAs single crystals is much lower than that in LEC-InAs, giving VGF-InAs better electrical and optical properties. The nature of the defects in InAs single crystals is discussed by considering the variation in stoichiometry and environment during the crystal growth processes.

Mechanism of free electron concentration saturation phenomenon in Te-GaSb single crystal**Project supported by the National Natural Science Foundation of China (Grant Nos. 61474104 and 61504131).

Te-doped GaSb single crystal grown by the liquid encapsulated Czochralski (LEC) method exhibits a lag of compensating progress and a maximum carrier concentration around 8×1017 cm−3. The reason for this phenomenon has been investigated by a quantity concentration evaluation of the Te donor and native acceptor. The results of glow discharge mass spectrometry (GDMS) and Hall measurement suggest that the acceptor concentration increases with the increase of Te doping concentration, resulting in the enhancement of electrical compensation and free electron concentration reduction. The acceptor concentration variation is further demonstrated by photoluminescence spectra and explained by the principle of Fermi level dependent defect formation energy.

Photoluminescene study acceptor defects in lightly doped n type GaSb single crystals

Lightly Te-doped GaSb samples grown by the liquid encapsulated Czochralski (LEC) method have been studied by Hall measurements and low-temperature PL spectroscopy. The results suggest that acceptor-related antisite is the dominant defect in n-type GaSb with low Te-doping concentration. As the Te concentration increases, gallium vacancy related defects become the main acceptor. A new band of around 665 meV is observed in the GaSb sample with the lowest Te-doping concentration. The variation of the acceptor defects and their influence on the electronic and optical property on the n-GaSb single crystal are discussed based on the results.

Chromium compensated gallium arsenide detectors for X-ray and γ-ray spectroscopic imaging

Semi-insulating GaAs material of 500μm thickness grown using the Liquid Encapsulated Czochralski (LEC) method has been compensated with chromium to produce high resistivity single crystals suitable for spectroscopic imaging applications. Results are presented for the performance of three small pixel detectors each with 80×80 pixels on a 250μm pitch, fabricated with metal contacts and bonded to a spectroscopic imaging ASIC. Current–voltage measurements demonstrated a material resistivity of 2.5×109Ωcm at room temperature. At an optimised bias voltage, the average energy resolution at 60keV (FWHM) was in the range 2.8–3.3keV per pixel. An analysis of the voltage dependent X-ray spectroscopy suggests that the electron mobility lifetime (μτe) for each detector is in the range 2.1–4.5×10−5cm2V−1. The spectroscopic imaging capability of the detectors is also demonstrated in X-ray absorption spectroscopy measurements.

D215 GaAs単結晶成長に及ぼす融液流動および温度分布の影響(OS-2:複合対流)

2D computer simulation assists in the decision of growth parameters to reduce the crystal defects of GaAs crystal in liquid encapsulated Czochralski (LEC) method. In this paper, we numerically investigated the reason why the 450mm-long crystal has more crystal defects than the 350mm-long crystal by comparing heat exchange, temperature distribution and velocity vector in the source melt at several stage of the growth. The simulation results indicated that large heat release from crystal and small heat release from crucible bottom are advantageous to the crystal growth with few defects. It is also necessary that forced convection and natural convection of GaAs melt is delicately controlled by the crucible rotation rate and the temperature distribution.

10.1007/s11445-008-2014-2

Microdefects in undoped and zinc-doped GaP single crystals grown by the liquid-encapsulation Czochralski method have been studied by X-ray diffuse scattering. In undoped GaP single crystals, deviation from stoichiometry increases from the beginning to the end of an ingot. The ingot end is characterized by enhanced precipitation of excess gallium with formation of platelike microdefects. With an increase in their size, stress relaxation around microdefects begins to manifest itself. Doping with zinc leads to a significant change in the microdefect formation pattern.

LEC growth of semi-insulating GaAs crystals in traveling magnetic field generated in a heater–magnet module

For the first time semi-insulating (SI) GaAs single crystals were grown by the liquid encapsulated Czochralski (LEC) method using a traveling magnetic field (TMF) system generated in a heater–magnet module (HMM). The system was developed within the framework of the KRIST MAG ˜ ® project. The HMM, that generates heat and TMF simultaneously, was placed closely around the crucible inside the chamber of the industrial CI 358 puller. Before the growth experiments the induced vertical Lorentz force density F Lz was evaluated by the weight force response of a dummy. First growth experiments at various f/ ϕ ratios ( f—frequency and ϕ—phase shift) were carried out. Interface morphology and temperature fluctuation strengths were analyzed by a striation technique. Etch pit density, carbon, residual impurity and EL2° contents as well as electrical properties of the as-grown TMF–LEC GaAs crystals were measured. A preliminary correlation between crystal qualities and field frequency has been noticed.

The appearance of superconductivity in GaP and GaAs samples highly doped withCr

Bulk GaAs and GaP samples, highly doped with Cr, were grown by the liquid encapsulatedCzochralski (LEC) method. Magnetic measurements revealed type I superconductivity withTc≈6.2 Kand Hc∼600 Oe, identical for both compounds. The presence of amorphous inclusions of gallium, due tospecific cellular structures of the defects in the crystals grown by the LEC method, mayexplain existing superconductivity as a result of a phase transition leading toβ-Ga during cooling down of the sample. Since the observed parameters are also close to theparameters characteristic for superconducting Ga II we are not ruling out this possibility.

Study of microdefects in GaP and GaPZn single crystals grown by the liquid-encapsulation Czochralski method

Microdefects in undoped and zinc-doped GaP single crystals grown by the liquid-encapsulation Czochralski method have been studied by X-ray diffuse scattering. In undoped GaP single crystals, deviation from stoichiometry increases from the beginning to the end of an ingot. The ingot end is characterized by enhanced precipitation of excess gallium with formation of platelike microdefects. With an increase in their size, stress relaxation around microdefects begins to manifest itself. Doping with zinc leads to a significant change in the microdefect formation pattern.

The appearance of clear ferromagnetism for p-type InMnP:Zn implanted with Mn of 1 at.%

The p-type InP:Zn was prepared by the liquid encapsulated Czochralski method and subsequently implanted with Mn + of 5 × 10 15 cm −2. The results of energy dispersive X-ray displayed that the concentration of incorporated Mn into InP:Zn is 1 at.%. The cross-sectional transmission electron microscopy showed that the thickness of Mn-incorporated layer was ∼300 nm. For photoluminescence measurements, the Mn-related optical transitions caused by incorporation of Mn were broadly observed at the energy region of 1.034, 0.985, and 0.958 eV. The samples clearly showed ferromagnetic hysteresis loops at 10 K, and the ferromagnetic behavior was observed to persist up to 360 K. Thus, the Curie temperature of Mn +-implanted InMnP:Zn (Mn ∼ 1 at.%) is expected to be above 300 K. It is found that a room-temperature-ferromagnetism of InMnP:Zn can be formed by ion implantation of a relatively low concentration of Mn (1 at.%).

Optical, structural, and magnetic properties of p-type InMnP:Zn implanted with the Mn (1 and 10 at.%)

The p-type InP:Zn was prepared by the liquid encapsulated Czochralski method and subsequently implanted with Mn + of 5×10 15 cm −2 (1 at.%) and 5×10 16 cm −2 (10 at.%). The results of energy dispersive X-ray showed that the concentrations of Mn incorporated into InP:Zn is about 1 and 10 at.%. For photoluminescence measurements, the Mn-related optical transitions of the InMnP:Zn samples annealed at 350 ∘C for 60 s and at 450 ∘C for 30 s with Mn (1 at.%) were broadly observed at the energy region around 1.0 eV. The InMnP:Zn samples implanted with Mn (1 at.%) clearly showed ferromagnetic hysteresis loops at 10 K, and the ferromagnetic behavior was observed to persist up to 291 K. Curie temperature ( T C ) at 291 K has originated from MnP. The InMnP:Zn samples implanted with Mn (10 at.%) were annealed at 350 ∘C for 60 s and at 450 ∘C for 30 s. Using transmittance electron microscopy, both single crystalline and polycrystalline structures containing MnP and InMn 3 sized ∼20 nm were observed depending on the annealing condition. These samples exhibited two different Curie temperatures: T C 1 at 291 K and another ( T C 2 ) well above 291 K. The high-temperature ferromagnetic behavior up to T C 1 and above T C 2 is believed to have originated from two magnetic MnP and InMn 3 phases, respectively.