Research | IKZ | 29-01-2024

Crystal growth – how does it work?

Are crystals grown in a similar way to bananas, apples or rare tulips? No, of course not! Crystal growth refers to a multiplicity of technical processes and methods that enable us to “grow” crystalline materials.

The most well-known process, but by far not the oldest one, was developed by Polish chemist Jan Czochralski here in Berlin, close to the current site of the Leibniz-Institut für Kristallzüchtung (IKZ). Over a hundred years later, the Czochralski method is still one of the most important processes in commercial semiconductor manufacturing, and continues to require constant refinement. At the IKZ, this is undertaken by a multinational team of scientists. Among them is Dr. Iryna Buchovska, who introduces us to the institute in the IKZ science clip to mark the 30th anniversary of the Forschungsverbund Berlin, taking us on a journey through the various departments at the IKZ.

Pulling a single crystal from the melt

The Czochralski method is also referred to as “pulling from the melt.” This term is a very good description of the process. A material is melted in a crucible. A small crystal, the seed crystal, is now dipped into the melt. Before the seeds start melting, it is slowly withdrawn from the melt under rotation. In the process, the crystal pulls some of the melt with it, which crystallizes on its surface. As a result, the initially small crystal continues to grow. Depending on the material, this can take several hours or even months. According to legend, Jan Czochralski developed the process using an inkwell as a crucible. The crystal he ultimately produced can only have been a few centimeters long and millimeters thick. Today, we have progressed much further. Czochralski-grown semiconductor crystals can now measure several meters in length and a few inches in diameter. These crystals grow in impressively large, high-tech plants.

Researchers from a variety of disciplines

And yet crystal growers are not the only people needed to produce and explore crystals. At IKZ, researchers from a wide variety of disciplines work together. The process requires expertise in physics, chemistry, materials science, plant construction, and computer science, to name just a few disciplines. Numerical simulations support and speed up the research process. For example, computers can model temperatures and flows in the melt during crystal growth. In this way, an inherently very time-consuming experiment can be digitally simulated at high speed, enabling scientists to optimize the growth process from the start. When developing particularly complex growth technologies, it is often beneficial to replicate large-scale experimental facilities on a small scale. These model facilities, usually made of glass, often provide substantial insights into the fundamental physical processes occurring during crystal growth. The Science Clip is very enlightening, with Dr. Kaspars Dadzis explaining how to translate the processes in advanced growing facilities to simpler model facilities, while maintaining their physical complexity.

More and more perfect crystalline materials

Quality control concludes the crystal growing process. Experts such as Dr. Andreas Fiedler characterize the crystalline materials, ensuring that the crystals and processes are suitable for a wide range of applications. Whether in laser technology, semiconductor electronics or diagnostics, our highly technological world would be inconceivable without crystals. More and more perfect crystalline materials are also needed to meet the ever-increasing demands placed on sensors, solar cells, transistors, etc. Even tiny impurities or slight defects in the crystal growth may cause malfunctioning of the devices on which they are based. As a result, the methods used to test their optical and electrical qualities must also continually improve in accuracy.

Crystal growing is not a technology that can be revolutionized single-handedly. Not even a Jan Czochralski would accomplish that today. It takes interdisciplinary teams of technicians, engineers and scientists from a wide range of backgrounds and specializations to significantly advance the technologies required for crystal growth and application. The Leibniz-Institut für Kristallzüchtung and the entire Forschungsverbund wish to offer all employees an open and tolerant working environment, actively promoting technological innovation in the process. The achievements of the last 30 years show that we have often succeeded in this endeavor. We hope to continue to meet current and future challenges with a diverse and competent team in the coming decades, helping to shape the technologies of the future with novel and astounding crystalline materials just as we shape today’s technology.

Text: Dr. Owen Ernst

The article was published in Verbundjournal 119 | 2022 with the focus on "30 years of FVB."

Video / Science Clip