Vertical Gradient Freeze

The Vertical Gradient Freeze (VGF) process is an established crystal growth method, specifically designed for the production of monocrystalline semiconductors. Unlike other processes, VGF operates without moving system components and relies exclusively on precisely controlled temperature profiles. This allows for the production of extremely pure and defect-free crystals—a crucial foundation for numerous high-tech applications.

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The process

During the VGF process, the starting material is placed in a crucible together with a seed crystal and melted completely. A vertical temperature gradient is then applied, enabling controlled solidification from bottom to top. The solidification front moves from the seed crystal through the material. The temperature is controlled either by targeted heating or by adjusting the temperature field—entirely without mechanical movement.

Typical Materials

Key materials grown using the VGF process include compound semiconductors such as gallium arsenide (GaAs), indium phosphide (InP), and cadmium telluride (CdTe), as well as sapphire (Al₂O₃) and calcium fluoride (CaF₂). These materials are essential for modern electronics, particularly in the field of optoelectronics, communications, high-frequency technology, and optical applications.

Vertical Gradient Freeze crystal growth system in a cleanroom environment

Relevant industries

Vertical gradient freeze systems play a crucial role in producing advanced materials for high-frequency technology and optical applications, enabling the manufacture of components such as GaAs and InP microwave amplifiers and transistors for fast signal processing in communications and radar, as well as high-purity calcium fluoride single crystals for demanding optical uses in the UV and IR range. Further relevant industries please find below:

Semiconductor

GaAs and InP are used as wafers for integrated circuits and high-frequency transistors—ideal for fast, energy-efficient computer chips and specialized electronics.
LEDs, laser diodes, and photodetectors based on GaAs, InP, and GaP enable efficient light emission and detection, for example in lighting, medical technology, and sensor applications.

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Medical

Vertical Gradient Freeze (VGF) enables the controlled growth of compound semiconductor crystals with low defect density and high material uniformity. In medical imaging, VGF is used to produce GaAs, InP, and CdTe/CZT for high‑precision detectors in X‑ray, CT, PET, and SPECT systems, where stable electrical properties and high sensitivity are essential for accurate diagnostics.

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Aerospace & Defense

Crystals produced using the Vertical Gradient Freeze (VGF) process—such as gallium arsenide, indium phosphide, cadmium telluride, and sapphire—are widely used in the aerospace and defense sectors. They are employed in high‑performance solar cells for satellites, radar systems, infrared and radiation detectors, as well as protective windows and optical components for sensors and LiDAR. With their exceptional crystalline quality, high reliability and long service life under extreme conditions, along with outstanding electrical and optical properties, these materials provide significant advantages for next‑generation aerospace and defense applications.

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The Flexible System for VGF Crystal Growth

Operator in cleanroom suit working with a Vertical Gradient Freeze crystal growth system

Kronos

The Kronos system has been specifically developed for the Vertical Gradient Freeze (VGF) process, enabling the production of monocrystalline compound semiconductors of exceptional quality.

A standout feature of Kronos systems is their high operating pressure: in the range of 10 to 40 bar, it is possible to crystallize materials whose components exhibit high vapor pressure. This makes Kronos ideal for crystals such as gallium arsenide (GaAs), which is processed at up to 10 bar in the standard version, and indium phosphide (InP), which can be grown at pressures up to 40 bar in a special version.

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