Liquid Encapsulated Czochralski Research Articles

Enhanced Curie temperature of InMnP:Zn—TC∼300K

P -type bulk InP was prepared by the liquid encapsulated Czochralski method and subsequently diffused with Mn by heat treatment after the evaporation of Mn on top of InP:Zn using a molecular beam epitaxy system. The characteristics of Mn-diffused InMnP:Zn were investigated by an energy dispersive x-ray spectroscopy, photoluminescence, and a superconducting quantum interference device magnetometer measurements. The samples were characterized by transmission electron microscopy and no evidence of secondary phase formation of InMnP:Zn was found. The results of energy dispersive x-ray peak displayed injected concentration of Mn near 3%. The results of photoluminescence measurement showed that optical broad transitions related to Mn appeared around 1.2eV and it was confirmed that the transitions around 1.2eV were Mn-related band by the diffusion of Mn into InP:Zn. Clear ferromagnetic hysteresis loops were observed at 10 and 300K and the temperature-dependent magnetization showed ferromagnetic behavior around 300K, which is caused by carrier-mediated ferromagnetism in InMnP:Zn. It is found that a ferromagnetic semiconductor at room temperature can be formed in diluted magnetic semiconductor based on GaMnN and InMnP additionally co-doped with Mg and Zn, respectively.

Electron irradiated liquid encapsulated Czochralski grown undoped gallium antimonidestudied by positron lifetime spectroscopy and photoluminescence

Electron irradiated undoped liquid encapsulated Czochralski (LEC) grown GaSb sampleswere studied by positron lifetime spectroscopy (PLS) and photoluminescence (PL).In addition to the 315 ps component reported in the previous studies, anotherdefect with a lifetime of 280 ps was also identified in the present electron irradiatedsamples. The bulk lifetime of the GaSb material was found to be 258 ps. TheVGa,280 ps andthe VGa,315 ps defects were associated with two independent Ga vacancy related defects having differentmicrostructures. The well known 777 meV PL signal (usually band A) was alsoobserved in the electron irradiated undoped GaSb samples. The band A intensitydecreases with increasing electron irradiation dosage and it disappears after the300 °C annealing regardless of the irradiation dosage. The origin of the band A signal is alsodiscussed.

Role of electrode technology in radiation detector based on semi-insulating InP in development of detector array

In this work the role of electrode technology of a radiation detector based on Liquid Encapsulated Czochralski semi-insulating (SI) InP is investigated with emphasis on the development of a monolithic array of pixel detectors. Two different electrode technologies are applied: (i) Au evaporation to form a metal–semiconductor–metal structure with a quasi-Schottky barrier, and (ii) MOCVD of a p+ layer for the creation of a pin structure using the same SI InP base. The I–V characteristics and pulse height spectra of 241Am and 57Co are measured at room and lower temperatures and evaluated. The observed results show different electrical as well as detection performance of fabricated structures. Mechanical sawing and wet etched trench methods are applied with the aim of reducing electrical charge inter-diffusion between neighbouring strip detectors as a preliminary study to the fabrication of a segmented, monolithic detector array based on SI InP. SM and I–V methods are used for the evaluation of the wet chemical process used. The observed results and future works are discussed in view of results obtained within the study.

Study of indium phosphide wafers treated by long time annealing at high temperatures

High purity InP crystals were grown by liquid encapsulated Czochralski method from undoped InP melt. Wafers from the grown crystals were annealed in phosphorus ambient for 95 hours at 950 °C and cooled slowly. Conversion to semi-insulating state by annealing was studied by temperature dependent Hall measurements and low temperature optical absorption spectroscopy.

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.

Three-dimensional modeling of melt flow and interface shape in the industrial liquid-encapsulated Czochralski growth of GaAs

The heat transport in the melt and in the crystal including the interface shape was numerically investigated by local, fully three-dimensional (3D), time-dependent simulations for an industrially sized liquid-encapsulated Czochralski setup for growing GaAs crystals with 150 mm diameter. The thermal boundary conditions for the local 3D simulations were obtained from global quasi-steady 2D simulations. It was found that the type of thermal boundary conditions (fixed temperature or heat flux) has a strong influence on the 3D results of the interface shape and on the melt convection. Furthermore, a high sensitivity of the interface deflection on the temperature at the bottom wall of the crucible is observed. For a control of the interface shape the use of two types of magnetic fields (horizontal and vertical) was considered. It was found that a horizontal magnetic field has a bigger influence on the interface shape than a vertical magnetic field.

Mn-implanted dilute magnetic semiconductor InP:Mn

Unintentionally doped bulk InP was prepared by the liquid encapsulated Czochralski method and subsequently implanted with various doses of Mn+. The properties of Mn+-implanted InP:Mn were investigated by various measurements. The results of energy dispersive x-ray peaks displayed injected concentrations of Mn of 0.8% and 8.8%, respectively. The results of photoluminescence (PL) measurement showed that optical broad transitions related to Mn appeared near 1.089, 1.144, and 1.185 eV in samples with various doses of Mn+. It was confirmed that the photoluminescence peaks near 1.089, 1.144, and 1.185 eV were Mn-correlated PL bands by the implantation of Mn. Ferromagnetic hysteresis loops measured at 10 K were observed and the temperature-dependent magnetization showed ferromagnetic behavior around 90 K, which almost agreed with the theoretical prediction (Tc∼70 K).

Study on the perfection of in situ P-injection synthesis LEC-InP single crystals

Undoped, S-doped and Fe-doped InP crystals with diameter up to 4-inch have been pulled in 〈1 0 0〉-direction under P-rich condition by a rapid P-injection in situ synthesis liquid encapsulated Czochralski (LEC) method. High speed photoluminescence mapping, etch-pit density (EPD) mapping and scanning electron microscopy have been used to characterize the samples of the single crystal ingots. Dislocations and electrical homogeneity of these samples are investigated and compared. By controlling the thermal field and the solid–liquid interface shape, 4-inch low-EPD InP single crystals have been successfully grown by the rapid P-injection synthesis LEC method. The EPD across the wafer of the ingots is less than 5×10 4 cm −2. Cluster defects with a pore center are observed in the P-rich LEC grown InP ingots. These defects are distributed irregularly on a wafer and are surrounded by a high concentration of dislocations. The uniformity of the PL intensity across the wafer is influenced by these defects.

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.

Pure and intentionally doped indium phosphide wafers treated by long time annealing at high temperatures

High-purity InP crystals were grown by the liquid encapsulated Czochralski method from undoped InP melt and from the melt doped with Ca, Zn, Fe or Mn or co-doped with Ti and Zn. Wafers from the grown crystals were annealed in phosphorus ambient for 95 h at 950 °C and cooled slowly. Conversion to the semi-insulating state by annealing was studied by temperature-dependent Hall measurements and low-temperature optical absorption spectroscopy. The undoped samples with electron concentration below 1 × 1016 cm−3 became semi-insulating due to the decreasing content of shallow donors and the increasing content of the active Fe2+ deep acceptors. The narrow absorption line of hydrogen vibrations in the complex VInH4 disappeared after annealing and three new narrow lines appeared instead. Besides, new lines appeared which were interpreted as due to Fe2+ featured by a nearby lattice defect. The n-type InP lightly doped with Zn became semi-insulating due to the formation of a new deep acceptor level at 0.33 eV below the conduction band edge.

6-in diameter InP single crystals grown by the hot-wall LEC method and the mirror wafers

6-in diameter Fe-doped semi-insulating InP single crystals have been grown by the hot-wall liquid encapsulated Czochralski method. This method has a quartz inner vessel to stabilize the thermal convection. Temperature gradient and solid-liquid interface shape can be controlled by a multizone heater system. The weight of grown crystal was 18 kg and the full length was 250 mm. The dislocation density was about 1/spl times/10/sup 5/ cm/sup -2/. The resistivity was more than 1/spl times/10/sup 7/ /spl Omega/cm and its uniformity was the same as the smaller diameter crystal. The conditions of wafer processing were optimized to improve the wafer flatness. The rolloff and the slope of the wafer surface could be reduced especially by the improvement of the polishing conditions. The typical total thickness variation was 3.3 /spl mu/m, and it was comparable to the GaAs wafer.

A comparative study of EL2 and other deep centers in undoped SI GaAs using optical absorption spectra and photoconductivity measurements

The performance of radiation detectors fabricated from semi-insulating (SI) GaAs is highly sensitive to EL2 +-concentration in the material. Near-infrared optical absorption measurements are commonly used to determine the EL2-concentration and to roughly estimate the EL2 +-concentration under the assumption that the optical absorption is mainly determined by the photoionization and the photoneutralization of EL2 0 and EL2 +, respectively. However, the presence of different native defects can contribute to optical absorption and reduce the precision of determination of EL2-concentration. In this work, we evaluate the contributions into optical absorption from EL2 and other deep center namely EL3 defect (0.55 eV) using near-infrared optical absorption and photoconductivity (PC) measurements in the photon energy interval 0.5–1.4 eV for SI GaAs crystals grown by the liquid encapsulated Czochralski method from melts with As content changing from 50% to about 46%. The photoelectrical spectra were measured on p–i–n structure detectors with heavily doped p + and n + layers grown by Liquid Phase Epitaxy and on Schottky diodes. The short circuit photocurrent spectra were registered for all detectors in the energy interval 0.65–1.4 eV. Unexpectedly, the current sensitivities in the regions of the extrinsic and intrinsic absorption were comparable. A comparative study of optical absorption, PC and short circuit photocurrent spectra resulted in determination of EL2 +-concentration. It was concluded that contribution of additional deep centers, particularly the ionized EL3 + defect could be comparable to the EL2-contribution. The EL3 centers were attributed to oxygen-related defects based on published results and on some indirect evidence in our experimental data.

The effect of nitrogen implantation on structural changes in semi-insulating InP

110 keV nitrogen ions (N +) of fluences 1 × 10 14–1 × 10 17 cm −2 have been implanted in liquid encapsulated Czochralski grown Fe-doped semi-insulating indium phosphide (InP) single crystal substrates. Grazing incidence X-ray diffraction measurements on as-grown and implanted samples have been carried out and analyzed. At all above fluences, a broad hump in the region of InP(1 1 1) peaks is observed. It might have resulted from implantation-induced misoriented grains along certain preferred orientations. The peak observed at a d-value of 1.77 Å for all the fluences becomes more pronounced as the implantation fluence increases up to 1 × 10 16 cm −2. This could indicate formation of an Indium phosphide nitride alloy. Post-implantation annealing reduces the structural defects and assists in the growth of the nitride phase.

Modeling analysis of liquid encapsulated Czochralski growth of GaAs and InP crystals

AbstractThe results of three‐dimensional unsteady modeling of melt turbulent convection with prediction of the crystallization front geometry in liquid encapsulated Czochralski growth of InP bulk crystals and vapor pressure controlled Czochralski growth of GaAs bulk crystals are presented. The three‐dimensional model is combined with axisymmetric calculations of heat and mass transfer in the entire furnace. A comprehensive numerical analysis using various two‐dimensional steady and three‐dimensional unsteady models is also performed to explore their possibilities in predicting the melt/crystal interface geometry. The results obtained with different numerical approaches are analyzed and compared with available experimental data. It has been found that three‐dimensional unsteady consideration of heat and mass transfer in the crystallization zone provides a good reproduction of the solidification front geometry for both GaAs and InP crystal growth.

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.

Magnetic field effects during liquid-encapsulated Czochralski growth of doped photonic semiconductor crystals

During the liquid-encapsulated Czochralski (LEC) process, a single compound semiconductor crystal such as indium phosphide or gallium antimonide is grown by the solidification of an initially molten semiconductor contained in a crucible. The motion of the electrically conducting molten semiconductor can be controlled with an externally applied magnetic field. This paper presents a model for the unsteady transport of a dopant during the LEC process with a steady axial magnetic field. The convective species transport during growth produces significant segregation in both the melt and the crystal. Dopant distributions in the crystal and in the melt at several different stages during growth are presented.

Prediction of the melt/crystal interface geometry in liquid encapsulated Czochralski growth of InP bulk crystals

Prediction of the crystallization front geometry largely affecting crystal defects and growth stability is a crucial issue in numerical simulation of InP liquid encapsulated Czochralski (LEC) growth. In this paper, a comprehensive numerical analysis using various two-dimensional (2D) steady and 3D unsteady models is performed. A 3D unsteady model including the interface shape calculation is presented for the first time. The 3D model is combined with axisymmetric calculations of heat and mass transfer in the entire LEC furnace. Results obtained with different numerical approaches are analyzed and compared to available experimental data.

Flow characteristics of two immiscible liquid layers subjected to a horizontal temperature gradient.

Marangoni convection, driven by an interfacial instability due to a surface tension gradient, presents a significant problem in crystal growth in normal microgravity environments. It is important to suppress and control the convection phenomenon for better material processing, especially in crystal growth by the liquid encapsulated Czochralski or liquid encapsulated floating zone techniques, in which the melt is encapsulated in an immiscible medium. Marangoni convection can occur on the liquid-liquid interface and on the gas-liquid free surface. Buoyancy driven convection can also affect and complicate the flow. In the study we report here, experiments were carried out with two liquid layers, silicone oil and fluorinert, in an open and enclosed rectangular cavity. The flow in the cavity was subjected to a horizontal temperature gradient. The interactive flow near the liquid-liquid interface was measured by the particle image velocimetry technique. The measured flow field is in agreement with numerical predictions. Free surface fluctuations with several dominant frequencies were also measured.

Magnetic stabilization of the buoyant convection in the liquid-encapsulated Czochralski process

This paper presents a linear stability analysis for the buoyant convection during the liquid-encapsulated Czochralski growth of compound semiconductor crystals with a steady, uniform, vertical magnetic field. Results are presented for two values of the Prandtl number, corresponding to indium-phosphide (InP) and gallium-arsenide (GaAs). Most of the results are for a melt depth equal to the crucible diameter, but some results are also presented for a smaller depth. For the cases considered here, the instability involves a transition from a steady axisymmetric flow to a steady nonaxisymmetric flow corresponding to the first Fourier mode in the azimuthal direction. For the weaker magnetic fields, the critical Rayleigh number is close to that for the Rayleigh–Bénard instability in a vertical cylinder. For the stronger magnetic fields, the critical Rayleigh number for GaAs is higher than that for InP because convective heat transfer in the GaAs base flow reduces the vertical temperature gradient.

Controlled vapor-pressure heat-treatment effect on deep levels in liquid-encapsulated czochralski-grown GaP crystals

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of Ec-1.1 eV, Ec-1.6 eV, Ec-1.9 eV, and a hole trap of Ev+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the Ec-1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both Ec-1.1 eV and Ec-1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of Ec-1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that Ec-1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.