Simulating microgravity conditions for crystal growth

Germanium single crystals (GSCs), valued for their electrical and optical applications, suffer from the effects of melt convection during crystal growth. Melt conventions introduce defects by disturbing the shape and temperature at the solid-liquid interface (SLI). Space-based microgravity experiments suppress melt convection, but of course, they are too costly for industrial contexts.

To find an alternative approach, Feng et al. studied the application of a high magnetic field (HMF) in GSC growth. The goal was to simulate a microgravity environment where diffusion enables uniform solidification; similarly, a sufficient HMF limits velocity fluctuations in liquid germanium, leading to energetically favorable conditions for stable crystal growth.

The team found that a 10 tesla HMF induces a transition from convective to diffusive-controlled states, reducing dislocation density — structural perturbations that disrupt the crystal lattice — by over 35%. This finding is important for nucleation kinetics. As thermal diffusion dominates heat transfer, the thermal boundary layer expands, lowering the nucleation rates of unwanted crystals.

Also key to the production of defect-free GSCs is a planar SLI, which creates uniform temperature distributions and can be achieved through controlling the localized thermoelectromagnetic flow at the interface. Simulations confirmed how the HMF flattened the originally convex SLI during directional solidification.

Ultimately, high-quality, defect-free GSCs are vital to semiconductor development, which the authors plan to further explore.

“Our future work will deepen the understanding of HMF-assisted crystal growth by clarifying the coupling among magnetic field intensity, thermoelectromagnetic effects, and interface evolution,” said author Wenhao Lin. “We will evaluate scalability for large-diameter germanium crystals and explore extending this approach to other semiconductors such as silicon, gallium arsenide, and cadmium zinc telluride.”

Source: “Tailoring high-quality germanium crystal via high magnetic field,” by Meilong Feng, Congjiang Zhang, Zhuolin Li, Bangfei Zhou, Zhe Shen, Qiang Li, Biao Ding, Peijian Shi, Zhongze Lin, Weili Ren, Wenhao Lin, Tianxiang Zheng, and Yunbo Zhong, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0312731 .