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1.      A polycrstalline rod is mounted vertically inside a chamber, which may be under vacuum or filled with an inert gas.

2.      A needle-eye coil that can run through the rod is activated to provide RF power to the rod, inducing strong edy current and melting a 2-cm long zone in the rod.

3.      The movement of the molten zone through the entire length of the rod purifies the rod and forms the near-perfect single crystal.

4.      The process may be repeated several times to obtain high purity single crystal.

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The Bridgman method is a popular way of producing certain semiconductor crystals for which the Czochralski process is more difficult, such as gallium arsenide.

Stockbarger method

Bridgman Furnace

Bridgman method

■ Principle & Process

Heating polycrystalline material above its melting point and slowly cooling it from one end of its container, where a seed crystal is located.

Stockbarger method: As a pulling method like Czochralski method, boat pulled out through temperature gradient

Bridgman method: Melt is inside a temperature gradient furnace

■ Characteristics

The shape of the crystal is defined by the container

Drawback: Material is constantly in contact with crucible or sample boat, which introduces mechanical stress that possibly changes ideal crystal structures.

■ Usages & Applications Simple and popular way to producing semiconductor crystals such as GaAs, InP, CdTe.

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Liquid Encapsulated Czochralski Crystal Growth (LEC)

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Liquid Encapsulated Czochralski Crystal Growth (LEC)

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1. The starting materials  polycrystalline chunks or, in the case of semi-insulating GaAs, elemental Ga and As) are placed in the growth crucible along with a pellet of boron trioxide. The crucible is placed inside a high pressure crystal puller and heated up.

2. At 460°C the boron trioxide melts to form a thick, viscous liquid which coats the entire melt, including the crucible (hence, liquid encapsulated). This layer, in combination with the pressure in the crystal puller, prevents sublimation of the volatile group V element.

3.The temperature is increased until the compound synthesises (temperatures and pressures are varied depending on which material is being produced). A seed crystal is then dipped, through the boron trioxide layer, into the melt. The seed is rotated and slowly withdrawn and a single crystal propagates from the seed.

4.Crystal growth is monitored by the use of CCTV

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The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors.

The Working Principle of CZ
1. A fused silica crucible is loaded with a charge of undoped high quality polycrystalline Si.

2.  The gases inside the growth chamber are then evacuated.

3. The growth chamber is then back-filled with an inert gas to inhibit the entrance of atmospheric gases.

4. High quality Si charge inside the crucible is melted at melting point of Si (1421 °C).

5. A seed crystal, mounted on a rod, is dipped into the molten silicon.

6. The seed crystal's rod is pulled upwards and rotated at the same time, while this withdrawal process produce a roughly circular cross-section crystal.

7. As the seed crystal is pulled from the melt, it draws with it a
layer of molten material.