Compositional variation in AlGaAs crystals grown by LPE under microgravity and terrestrial conditions

Abstract We grew AlGaAs crystals on GaAs substrates from solutions aboard the Japanese free-flying satellite SFU, using low temperature range type isothermal heating furnaces. Six GaAs substrates forming a cube eliminate the free surface from the solution, which causes surface tension-driven convection. The samples were heated to 850°C to make Al–Ga–As solutions by dissolving the GaAs substrate surfaces into the Al–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 convectionless conditions. The surface morphology of the μ-g sample was much smoother than that of the 1-g sample. The growth thickness difference in the six substrates used in the μ-g experiments was much less than that of those used in the 1-g experiments. These facts prove that convectionless growth was achieved. The Al composition in the crystal decreases as the distance from the growth interface increases. This decrease in the μ-g sample is more gradual than that in the 1-g sample. Our calculational results using a theoretical model maintaining phase-equilibrium together with the constancy of diffusion flux at the growth interface at the same time showed the same tendency, while conventional diffusion-limited model results in opposite tendency. These results prove that our model for calculating compositional variation in ternary LPE layers correctly expresses diffusion-limited growth conditions.