Float Zone (FZ) Technique of Crystal Growth
Theory
The Float Zone (FZ) technique is a method used to grow ultra-high purity single crystal materials, especially silicon.
In this method, a small region of a solid rod is melted and moved along its length. Impurities concentrate in the molten zone and move with it, resulting in a highly pure crystal.
Also known as: Zone Refining Method
Principle
A moving molten zone carries impurities along the rod, leaving behind purified solid crystal.
Process Steps
- Starting Material: Polycrystalline silicon rod
- Seed Crystal: Attached at one end
- Heating: RF coil creates a localized molten zone
- Zone Movement: Molten region moves along the rod
- Crystal Growth: Material solidifies into single crystal
- Impurity Removal: Impurities move to one end
Advantages
- Very high purity crystal
- No contamination from crucible
- Low oxygen content
Disadvantages
- Expensive process
- Limited crystal size
- Complex control
Applications
- Power semiconductor devices
- High-frequency electronics
- Research applications