Growth Of ZnSe Single Crystals Research Articles

溶液成長法によるZnSe単結晶の成長 : バルク成長 I フラックス法

溶液成長法によるZnSe単結晶の成長 : バルク成長 I フラックス法

Thermodynamic analysis and growth of ZnSe single crystals in Zn-Se-I2 system

A modified chemical vapor transport system is developed to grow ZnSe single crystals from zinc–selenium source materials, where iodine serves as the chemical transport agent to avoid the kinetics limitations of the congruent sublimation conditions. ZnSe crystals with different crystalline quality are obtained under various growth conditions. The thermodynamic properties of Zn-Se-I2 system are studied by combining the mass conservation with the vapor-solid reactions related to crystal growth. The mass transport is analyzed by using the diffusion-convection mathematical model. Depending on initial iodine concentration and the designed temperature difference between source zone and growth zone, the optimum growth conditions can be predicted based on the calculated maximum growth rate. Comparing growth results with theoretical analysis indicates that Zn-Se-I2 system affords a feasible route to grow ZnSe crystals. High quality ZnSe crystal can be achieved under the theoretically optimized growth conditions.

Growth of ZnSe single crystals from Zn–Se–Zn(NH 4) 3Cl 5 system

A modified chemical vapor transport method in a closed-tube system was developed to grow ZnSe single crystals from zinc–selenium –Zn(NH 4) 3Cl 5 system, where Zn(NH 4) 3Cl 5 served as the chemical transport agent to avoid the kinetics limitations of the congruent sublimation conditions to ZnSe crystals growth. The growth temperature of 1001–1005 °C was employed. The ZnSe crystal with a dominated (1 1 1) singular face was obtained. The structure characteristic and crystalline quality of as-grown ZnSe single crystal were investigated by several methods such as XRD, rotating orientation X-ray diffraction, double-crystal diffraction, photoluminescence spectrum and optical microscope. The infrared transmission spectra and ultraviolet absorption measurement of as-grown crystal were also reported. The microscopic observation on the surface of as-grown ZnSe crystal revealed that two-dimension dendrite crystal growth governs the crystal growth in the system. Comparing this result with the growth of ZnSe–Zn(NH 4) 3Cl 5 system suggested that ZnSe single-crystal grown directly from two elements in one step has lower purity and quality than ZnSe crystal grown from ZnSe polycrystal source system.

Thermodynamic Calculations and Growth of ZnSe Single Crystals by Chemical Vapor Transport Technique

A thermodynamic model has been proposed for the growth of ZnSe single crystals by the chemical vapor transport (CVT) method using iodine as the transporting agent. The optimum growth conditions for the growth of good quality ZnSe single crystals have been investigated theoretically using partial pressure values of I, I2, ZnI2, and Se2, which were calculated empirically at different growth temperatures and for different iodine concentrations, present inside the growth ampule. The diffusion-limited transport rates have also been calculated by taking into consideration the growth temperature, the ampule length, the total pressure present inside the ampule, and the partial pressures of ZnI2 at growth and source zones. The change in supersaturation ratio with respect to temperature and initial iodine concentration has also been calculated using this numerical model. The optimum growth temperature for the ZnSe−I2 system has been predicted from the theoretical results. Experiments were carried out for the growth...

Crystal growth of zinc selenide under μ g-conditions

The CVT growth of ZnSe single crystals under micro-gravity (μ g)-conditions was investigated in comparison with the corresponding ground-based (1 g) experiments. The transport rates have been found to be considerably higher than the computed values accounting mainly for diffusion and Stefan flow. Different types of convection may be masked or superimposed by thermal convection when under 1 g-conditions. The quality of μ g-grown crystals was improved even at such high mass transport rates that arise at 1 g-experiments.

Contactless growth of ZnSe single crystals by physical vapor transport

ZnSe crystals were grown by self-seeded physical vapor transport (PVT) technique in the horizontal configuration. The source materials were heat treated by H 2 reduction to remove the oxides followed by baking under dynamic vacuum to adjust the source composition toward that of congruent sublimation. Contactless growth of ZnSe single crystals have been performed using three different source materials. The crystals grew away from the ampoule wall with large (1 1 0) facets tending to align parallel to the gravity direction. The SEM micrographs and the AFM images showed that large (1 1 0) terraces and steps dominate the as-grown facets. The measured residual gas pressure and composition (mostly CO and H 2) in the processed ampoules were similar for all source materials used. One-dimensional diffusion model on the mass flux of a multi-species PVT system was employed to analyze the conditions for contactless growth. The calculated thermal profile for supersaturation is very close to the thermal profile measured inside the empty furnace bore in the region of contactless growth. The effects of convective flows in the vapor phase inside the ampoule on the growth processes are discussed.

Vapour growth and doping of ZnSe single crystals

The results of seeded vapour-phase free growth of ZnSe single crystals in both the 〈1 1 1〉 and 〈1 0 0〉 directions are presented and discussed. Optimum growth conditions were found to be essentially different for these two directions. The doping by In and Al from both vapour phase during the growth process at T=1180–1240°C and liquid phase by means of annealing in liquid Zn with In or Al additions at T=900–950°C was performed. To characterize grown crystals, selective chemical etching, X-ray diffraction rocking curve, cathodoluminescence study, atomic-emission analysis, specific resistance and Hall effect measurements were carried out.

In situ observation of twin formation during the growth of ZnSe single crystals from the vapor phase

Single crystals of ZnSe are grown by sublimation in closed ampoules of fused silica at temperatures between 1300 and 1400 K. With a video camera it is observed that the crystals develop preferably {1 1 0} faces. The free corner of three {1 1 0} faces appears as the preferred place of formation of a nucleus in twinned position. Repeated twin formation leads to a dominant growth in the 〈1 1 1〉 direction. In the presence of SiS 2, however, {1 0 0} and {1 1 1} faces appear near equilibrium and twins form on {1 1 1} faces resulting in a preferred growth in 〈1 1 2〉 directions. These observations are qualitatively explained by an idealized atomic arrangement of growth steps.

Growth of ZnSe single crystal by CVT method with self-moving convection shield

The self-moving convection shield was used in the growth of ZnSe single crystal by chemical vapor transport method using iodine as a transport agent. The reduction of the convection enables the growth of a 1-in diameter ZnSe single crystal. The incorporation efficiency of iodine on (1 1 1)B facet was proved to be larger than that on (1 0 0) facet. Impurity-hardening effect of incorporated iodine in the grown ZnSe crystal is also suggested.

Growth of large ZnSe single crystal by CVT method

The growth of ZnSe single crystals by chemical vapor transport (CVT) method using iodine as transport agent was investigated for the purpose of growing a large ZnSe crystal with a diameter of 1 in. The optimum growth temperature, seed orientation associated with the angle at the conical tip and iodine concentration were determined from the viewpoint of high growth rate and morphological stability. A 1″∅ ZnSe single crystal was successfully grown under determined growth conditions.

Seeded vapour-phase free growth of ZnSe single crystals in the 〈1 0 0〉 direction

Seeded vapour-phase free growth of ZnSe single crystals at T g = 1100–1250°C in 〈1 0 0〉 direction was studied. The 〈1 0 0〉 growth process was found to be more sensitive to the temperature profile in a furnace than the 〈1 1 1〉 direction. The problem that seed attachment to a support pedestal is followed by a generation of high dislocation density was solved by use of a reverse temperature gradient along the axis of the furnace between the seed and the pedestal and by optical monitoring of the attachment process during the growth. Seeds with dislocation density of 10 4–10 5 cm −2 and 2–4 cm 2 area selected from single crystals grown in 〈1 1 1〉 direction were used for the first growth processes in 〈1 0 0〉 direction. To increase the diameter of the grown crystals, a tangential growth regime was developed. Twin free ZnSe single crystals of 51 mm diameter and of 15 mm height were grown in helium. The average dislocation density was about 10 4 cm −2 and the full-width at half-maximum (FWHM) of the X-ray rocking curve was as small as 16 arcsec.

Seeded vapour-phase free growth of ZnSe single crystals in the 〈1 0 0〉 direction

Seeded vapour-phase free growth of ZnSe single crystals in the 〈1 0 0〉 direction

Melt growth of ZnSe single crystals with B 2O 3 encapsulant: the role of solid-solid phase transformation on macro defect generation in ZnSe crystals

B 2O 3 is an available encapsulant for the melt growth of ZnSe single crystals with a limited degree of contamination of boron, 10 16−6 × 10 18 atmos cm −3. It is effective to reduce the density of twins in ZnSe crystals. Through the consideration of the role of B 2O 3 encapsulant, the generation process of three specified structures of melt-grown ZnSe crystals was interpreted. It is attributed to the different solid-solid transformation mechanisms governed by the nucleation process of the zincblende phase.

GroWth of ZnSe Single crystals by the sublimation method

GroWth of ZnSe Single crystals by the sublimation method

ZnSe epitaxial growth by the temperature difference method under controlled vapor pressure (TDM-CVP) using Se solvent

We performed epitaxial growth of ZnSe single crystals by the temperature difference solution growth method with and without a Zn over pressure and using Se as solvent. In case of undoped epitaxy the surface morphologies as well as the cathodoluminescence (CL) spectra depend greatly on the growth temperature which was variant between 650–950°C. Uniform surface morphologies were obtained at a growth temperature of 950°C. On the other hand, the intensity of the CL spectra increases at lower growth temperature. By controlling the Zn vapor over pressure at a certain optimum value above the Se solution, the intensity of the exciton emission was found to increase even at a high growth temperature. Also, all of the epitaxial crystals grown under applied Zn vapor pressure with doped impurities, Na and Li, showed p-type conductivity.

The growth of ZnSe single crystals by physical vapor transport

Zinc selenide single crystals have been grown in sealed quartz ampoules by the physical vapor transport method. Complete transport of the starting material and single site growth have been achieved with no material adhering to the ampoule wall. Growth is initiated in a narrow channel in the cold finger attached to the growth end of the ampoule. The highest growth rate to date has been 280 mg/day which corresponds to an average transport rate of about 1.93 mmol/day. The largest single crystal, measuring 1 cmX4 mmX2 mm, had a total growing time of 11 days or an average growth rate of 171 mg/day. Polished wafers cut from the crystals have been etched and examined by optical and electron microscopy. No impurities or unwanted phases were detected, but frequent twinning occurs. Etch pit densities on (111) surfaces are as high as 10 6 cm −2.

Growth of ZnSe single crystals by iodine transport

Large ZnSe single crystals (14x14x20 mm 3) have successfully been grown from the vapor phase by iodine transport. Substrates with large area (10x10 mm 2) for epitaxial growth were prepared by cutting the crystal. It is important to control the temperature fluctuation and seed direction for rapid growth. As an etchant for the measurement of dislocation density, the NaOH solution on (111) B is better than the Br-CH 3OH solution on (111) A. The etch-pit density is (2–7)x10 4/cm 2. The iodine concentration in the crystal is about 200 ppm. The resistivity of the ZnSe crystal annealed in molten Zn is 0.03 Ω cm.