COMPOSITIONAL VARIATION IN ALGAAS CRYSTALS GROWN BY LPE UNDER MICROGRAVITY AND TERRESTRIAL CONDITIONS

We grew AlGaAs crystals on GaAs substrates from solutions aboard the J apanese free-flying satellite SFU, using low temperature range type is othermal heating furnaces. Six GaAs substrates forming a cube eliminat e the free surface from the solution, which causes surface tension-dri ven convection. The samples were heated to 850 degrees C to make Al-Ga -As solutions by dissolving the GaAs substrate surfaces into the AI-Ga solutions. Then the furnace temperature was reduced gradually to grow crystals from the supersaturated solution. The space experiments were carried out as planned, and AlGaAs crystals were grown under convecti onless conditions. The surface morphology of the mu-g sample was much smoother than that of the l-g sample. The growth thickness difference in the six substrates used in the mu-g experiments was much less than that of those used in the 1-g experiments. These facts prove that conv ectionless growth was achieved. The Al composition in the crystal decr eases as the distance from the growth interface increases. This decrea se in the mu-g sample is more gradual than that in the l-g sample. Our calculational results using a theoretical model maintaining phase-equ ilibrium together with the constancy of diffusion flux at the growth i nterface at the same time showed the same tendency, while conventional diffusion-limited model results in opposite tendency. These results p rove that our model for calculating compositional variation in ternary LPE layers correctly expresses diffusion-limited growth conditions. ( C) 1998 Elsevier Science B.V. All rights reserved.