International Journal of Science and Technology (IJST)

Diffusion controlled entirely detached growth of in₀.₅Ga₀.₅Sb by VDS process: Role of interface stability, thermodiffusion, and quasi-microgravity condition

This study reports, for the first time, the diffusion-controlled growth of In₀.₅Ga₀.₅Sb crystals under entirely detached conditions using the Vertical Directional Solidification (VDS) process in a vacuum-sealed quartz ampoule. The detached configuration eliminates crystal–wall contact, suppresses buoyancy-driven convection, and establishes a quasi-microgravity environment governed by diffusion and thermodiffusion. Crystal growth was achieved under controlled conditions of gap width (70–250μm), axial temperature gradient (10–32 °C·cm⁻¹), and translation rate (≤ 3 mm·h⁻¹), ensuring a stable and planar crystal–melt interface. Mass transport is governed by coupled Fickian diffusion and Soret-driven thermodiffusion, leading to systematic solute redistribution along the growth axis. A polarity transition from n-type to p-type conduction occurs near the equiatomic composition (~50% GaSb), confirming thermodiffusion-controlled segregation. Key transport parameters, including boundary layer thickness (δ ≈ 0.05–0.3 cm), diffusion time (~10² s), and a low Peclet number (Pe ≪ 1), confirm diffusion-dominated growth with negligible convection. The constitutional supercooling criterion is satisfied under detached conditions, ensuring interface stability and defect-free solidification. Structural, electrical, and optical characterizations confirm high crystalline quality, reduced dislocation density, and excellent compositional uniformity. A dimensionless diffusion framework is introduced to quantify the transition from gravity-influenced to diffusion-dominated regimes. The results demonstrate that the VDS process enables quasi-equilibrium and quasi-microgravity solidification and provides a viable terrestrial alternative to alike microgravity-based crystal growth of high-quality In₀.₅Ga₀.₅Sb.