Results of this period

(1)  Development of the concentration gradient partial melting method

Full paper: "Homogeneous In_0.3Ga_0.7As Crystal Growth by the Graded Solute Concentration Method" in PDF file (File Size: 649 KB)

Combining ideas of the graded solute concentration method and partial melting method, we have succeeded in growing homogeneous InxGa1-xAs single crystals with x = 0.2 to 0.33.   We simulated crystal growth in microgravity by the growth in capillary tubes with bores of 1.5 to 2.0 mm.   The maximum length of the homogeneous part was more than 20 mm and such long homogeneous crystals were obtained for the first time.   This shows the validity of the concentration gradient partial melting method.

(2)  Thermodynamic analysis of the concentration gradient partial melting method

Full paper: "Qualitative Description of the Concentration Gradient Partial Melting Method and Application to In_xGa_1-xAs" in PDF file (File Size: 2540 KB)

Solid-liquid reactions in the crystal growth by the concentration gradient partial melting method were examined and conditions for growing homogeneous In_0.3Ga_0.7As crystals were analyzed from a thermodynamic point of view.   Initial zone width and optimum growth rates were calculated varying concentration profile of feeds and they were compared with those obtained by experiments, giving the theoretical basis of the concentration gradient partial melting method.

(3)  Numerical analysis of InxGa1-xAs crystal growth conditions

Full paper: "Numerical Analysis of Crystal Growth of an InAs-GaAs Binary Semiconductor under Microgravity Conditions" in PDF file (File Size: 184 KB)

A numerical calculation method for the growth of the pseudobinary system in which the moving solid-liquid interface can be treated has been developed.   The method was applied to the In_xGa_1-xAs crystal growth and the effect of buoyancy convection induced by residual acceleration in space craft was investigated.   Even the small residual acceleration of 10^-6 g is found to disturb the concentration field in the melt and direction of residual acceleration to the growth axis has also great influence on it.   Influence of g-jitter and Soret effect is small compared with that of the residual acceleration.

(4)  InAs-GaAs interdiffusion coefficient measurements

Full paper: "InAs-GaAs interdiffusion measurements" in PDF file (File Size: 1028 KB)

Interdiffusion coefficients of the InAs-GaAs system and self diffusion coefficients of InAs in the system InAs-¹¹³InAs have been measured accurately for the first time by using the sounding rocket TR-IA#7 and the shear cell method combined with glass sealing technique in microgravity.   Measured diffusion coefficients were in the range between 1.2 to 4.1ﾗ10^-8 m²/s at temperatures between 1070 and 1200 degrees centigrade.   Two significant digits were obtained for regular compositional profiles.

(5)  Thermal diffusivity measurements of molten In_xGa_1-xAs

Full paper: "Measurements of Thermal Diffusivity of Molten InGaAs by the Laser Flash Method" in PDF file (File Size: 187 KB)

Thermal diffusivity of molten In_0.8Ga_0.2As was measured using the laser-flash method.   The sample In_0.8Ga_0.2As was sandwiched between thin graphite disks and sealed in a transparent quartz container with a flat window of sufficient strength to withstand the high vapor pressure of arsenic.   Thermal diffusivity is 10 ~ 12 mm²/s from melting point to 1150 degrees centigrade.

(6)  Preparation of feeds with concentration gradient of InAs

Full paper: "Preparation of InGaAs Starting Materials Having the Gradient InAs Concentration" in PDF file (File Size: 589 KB)

Graded In concentration feeds were prepared by directional solidification of In_xGa_1-xAs melt for x = 0.3, 0.5 and 0.7.   At a temperature gradient of 40～60 K/cm, sample translation rates are required to be lower than 1.5 mm/h for avoiding constitutional supercooling.   Profiles of solute concentration are similar to those obtained in the diffusion limited growth rather than those solidified in the complete mixing conditions.

(7)  In_xGa_1-xAs seed crystal growth by the multi-component zone melting method

Full paper: "In_0.3Ga_0.7As Seed Crystal Preparation Using The Multi-Component Zone Melting Method (II)" in PDF file (File Size: 228 KB)

In_0.3Ga_0.7As seed crystal preparation using the multi-component zone melting method is currently under way for space experiments.   In a sample configuration with an InAs crystal sandwiched between GaAs seed and feed crystals, the x-value of growing In_xGa_1-xAs crystal is increased from 0.03 to 0.3 before maintaining at 0.3 for several millimeters of growth.   The length of single crystalline In_0.3Ga_0.7As was increased from 4 to 6 mm and scattering of the x-value in a In_0.3Ga_0.7As layer was reduced from ｱ0.01 to ｱ0.005 this year.

(8)  Thermal analysis of sample devices

Full paper: "Reliability Investigation on Numerical Analysis by Comparison with Experimental Result" in PDF file (File Size: 1566 KB)

Temperature distribution of the growth ampoule and the cartridge were analyzed so as to obtain convex solid-liquid interface curvature, which is important for growing large single crystals.   A new code has been developed for the analysis of diameter change between a seed and growing crystal.   To treat the effect of convection in the melt, non-steady calculation has been performed for various gravity levels.   The interface shape is improved toward convex in microgravity but complete convex shape has not been shown yet.   Reactions of In_xGa_1-xAs melt with Ta and WC103 alloy was investigated in order to make use of cartridge safety.

(9)  Characterization of In_xGa_1-xAs feeds using Raman scattering

Full paper: "Analysis of Compositional Fraction in Polycrystalline In_xGa_1-xAs Using Raman Scattering" in PDF file (File Size: 155 KB)

As a non-destructive method for analyzing compositional profiles of feeds, micro-Raman scattering has been investigated.   Molar fractions evaluated by Raman scattering show good agreement with those obtained by conventional chemical analysis.   Spacial resolution of micro-Raman scattering is about 1 mm.   Therefore, micro-Raman scattering is confirmed to be one of the best non-destructive methods to analyze the compositional profiles in high spacial resolution for In_xGa_1-xAs feeds.