PAM-XIAMEN, a leading germanium ingot manufacturer, has germanium (Ge) crystals for sale. Due to its scarcity of resources, excellent optical and physical properties, germanium material is widely used in high-tech fields such as fiber optic systems, infrared optical systems, electronics and solar applications, detectors, and is an important functional material and structural material required by strategic industries. About the Ge crystal, the two main methods for germanium crystal growing we adopted are briefly introduced: Czochralski (CZ) and vertical gradient freeze (VGF). According to different germanium crystal properties, germanium crystals have different applications. Infrared optical Ge single crystal and high-purity Ge single crystal are analyzed in this article.
1. Parameters of Germanium Crystal
Item 1: PAM170113-GE
|N Type / Undoped
|> 50 ohm-cm
Item 2: PAM170628-GE
|4” Ge Single Crystal
|100.5 +/- 0.3 mm
|≥ 200 mm
|(111) +/- 2 Deg.
|> 40 ohm-cm
Item 3: PAM190423-GE
|(100) +/- 1 Deg.
|P Type/Ga Doped
Item 4: PAM210203-GE
|Optical Grade Germanium Crystal
|33 +/-0.3 mm
|> 30 ohm-cm
|Double Side Polished
2. Growing Methods of Germanium Single Crystal
Commonly used preparation methods of germanium single crystals mainly include Czochralski method and Bridgman method (Bridgman). The latter includes Horizontal Bridgman (HB), Vertical Bridgman (VB), and vertical gradient freeze (VGF). Other growth methods include heat exchange, Oriented crystallization method, etc. At present, Czochralski method and vertical gradient solidification method are widely used in the world.
Both the Czochralski method and the vertical gradient solidification method use 6N zone-melted germanium ingots as raw materials, and the growth of germanium single crystal is doped with different trace metal elements for different uses. The current germanium single crystal growth equipment adopts the manufacturing technology of silicon single crystal growth equipment. The growth equipment is modified according to the specific requirements of the growth thermal field, material properties, and size of the germanium single crystal.
Germanium(Ge) Crystal Structure
2.1 CZ Method for Germanium Crystal Growing
The Czochralski method mainly includes the processes of seeding, necking, shoulder setting, shoulder turning, equal diameter, and finishing. If the seed crystal is located above the melt, first find a suitable temperature point, and immerse the seed crystal into the zone-melted single crystal germanium ingot melt to form a non-uniform nucleation. The non-uniform nucleation is beneficial to reduce the critical subcooling degree and greatly increase the nucleation rate. Through the designed thermal field, the longitudinal and radial temperature distribution are effectively controlled, and then the seed crystal is rotated and pulled up at a certain speed, and the newly solidified crystal slowly grows into a single crystal on the seed crystal.
The key for germanium crystal growing by Czochralski method is to equip the single crystal furnace with a reasonable thermal field system. A better thermal field distribution should allow the longitudinal temperature gradient to be as large as possible to ensure sufficient power for germanium crystal growth without being too large, avoiding metacryst. The radial temperature gradient tends to zero as much as possible to ensure the stability of the crystalline interface. In addition, the equipment and technology of Czochralski method for growing single crystals are relatively simple. The CZ method is easy to realize automatic control, high production efficiency and easy to draw single crystals with larger diameters, which can better control the impurity concentration in the single crystals to meet the needs of different applications.
2.2 Ge Single Crystal Grown By VGF Method
The vertical gradient solidification law is just the opposite, the seed crystal is located below the melt.
Firstly breaking the zone-melted ingot type germanium, the surface is chemically treated, cleaned and dried, and put into a crucible (different from the graphite crucible of the Czochralski method, boron nitride crucible is generally used), and then vacuum-encapsulated with a quartz tube. The encapsulated quartz tube is placed in the germanium single crystal furnace according to the technical requirements.
Then, design the longitudinal and radial temperature gradients of the thermal field of the low dislocation growth type VGF furnace. According to the selected technical parameters, the computer program group control technology is programmed to realize the gradual heating and melting of the zone-melted germanium boule and the growth of the seed crystal. The set pulling speed is used to control the slow downward movement of the quartz tube, and the solid-liquid interface is precisely cooled to control the shape and growth rate of the crystal interface. Finally, the closed tube crystal annealing method is used to obtain a germanium single crystal with high uniformity and low stress.
Although the vertical gradient solidification method has a slow growth rate and low efficiency, the germanium crystal dislocations are low.
3. Germanium Single Crystal Material
3.1 Germanium Crystal Usage in Infrared Optics
Germanium single crystal for infrared optics is one of the most widely used infrared optical materials in the world, which is usually prepared by the Czochralski method.
In addition, the continuous development and maturity of infrared product-related technologies, resulting a lower cost of production, thereby the application of infrared Ge products in the commercial field has become more and more extensive, and its growth rate is much higher. Now the more mature applications are mainly in the prevention and detection of the electric power industry. With the rapid development and popularization of thermal imaging cameras in the fields of fire protection, engineering construction, security, forest fire prevention, and on-board systems, the infrared market for germanium single crystals has huge potential.
3.2 Challenges for Infrared Germanium Single Crystal Growing
At this stage, infrared germanium crystal growing is limited by growth equipment and technology. It is usually difficult to grow germanium single crystals with larger diameters. The global growth level is basically between φ300 and 400mm. In order to meet the special needs of airborne and shipborne germanium windows greater than φ500mm, the concept of quasi-single crystal in the silicon industry has been introduced into the germanium industry. Quasi-single crystals mainly include seedless ingot casting and seeded ingot casting. However, how to define quasi-single crystal technology has not yet reached a consensus, and there is no consensus and unified standard in the industry. This technology is a huge test for the R&D, design, and processing capabilities for semiconductor wafer labs.
3.3 High Purity Germanium Single Crystal Applications
Due to the special performance of the high-purity germanium crystal detector, it has not only become the first choice for experimental research in nuclear physics, particle physics, and astrophysics, but also has been gradually applied to many fields such as nuclear industry, medicine, customs inspection and so on.
3.4 High Requirements for HP Ge Crystal
High-purity germanium single crystal material is the highest-end germanium product in the world, with a purity of 13N, and is the core material for manufacturing high-purity germanium crystal detector (HPGe). In order to meet the requirements of the detector, the material properties of the germanium single crystal must be guaranteed. Therefore, the growth and preparation process of the germanium single crystal is extremely difficult.
For the high-purity germanium crystal growing, the germanium raw materials are purified by zone melting, and then the electrical properties are measured by van der Pauw Hall measurement method. If the impurity level of zone-melted germanium boule reaches 1010～1011 cm– 3. Compared with the original zone melted germanium ingot of 1013 ～1014 cm-3, it is reduced by 3 orders of magnitude. This purified zone melted germanium can be used to grow high-purity germanium single crystals. After the crystal is grown, X-ray diffraction analysis, Van der Powell measurement, photo thermal ionization spectroscopy (PTIS) and dislocation measurement are used to characterize the grown crystal. If the impurity level of the crystal reaches 109 ～1010 cm-3 and the dislocation density is between 102 ～104 cm-2, it can be used to make a detector. Therefore, during the preparation of high-purity germanium single crystals, it is essential to characterize the grown crystals.