Vapour Phase Crystal Growth Envelope with Bypass Evacuation Paths
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Solution Overview
Problem
Conventional methods for growing large, high-quality single crystals of cadmium telluride (CdTe) and cadmium zinc telluride (CZT) face challenges such as dislocations, sub-grain boundaries, twins, and zinc segregation, leading to impurities and inclusions, which affect detector performance, and require high temperatures, complicating the vacuum evacuation process.
Innovation Solution
The apparatus includes an envelope assembly with additional fluid communication paths upstream of the flow restrictors, allowing for rapid and high-quality evacuation during setup and maintaining a leak-tight environment during growth, using a multi-tube physical vapour phase transport method with independently controlled source and growth zones, and secondary flow paths to bypass the flow restrictors during evacuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional liquid phase or self-seeding vapour phase crystal growth methods are used, then crystal growth can be achieved, but dislocations, sub-grain boundaries, twins, and inclusions form easily, reducing crystal quality
Solution Approach 1:
The patent employs physical vapour phase transport to grow CdTe and CZT crystals, utilizing phase transitions of source materials (Cd, Zn, Te) from solid to vapour and then to solid crystal deposition. This vapour phase approach avoids liquid melt contamination and associated defects like inclusions and dislocations, achieving high-quality crystals with minimal harmful factors
Solution Approach 2:
The patent uses a vacuum environment (inert atmosphere) for crystal growth, maintaining pressures below 10^-3 Pa to prevent oxidation and contamination of source materials and growing crystals. This inert environment eliminates reactive gas interactions that could introduce impurities and defects, significantly improving crystal quality
2Stability of the object's composition
If high temperatures are used for CZT growth to strengthen the lattice, then zinc segregation is reduced, but the process forms precipitates and inclusions due to excess tellurium in the melt
Solution Approach 1:
The patent uses vapour phase transport instead of liquid phase growth, allowing CZT crystal formation through vapour deposition at controlled temperatures. This approach eliminates the liquid melt phase that causes tellurium inclusions and precipitates, while still achieving compositional uniformity through controlled vapour transport and deposition
Solution Approach 2:
The patent optimizes temperature parameters in the vapour phase process, maintaining source zone temperatures of 600-900°C and growth zone temperatures of 400-700°C. These parameter changes enable controlled vapour transport and deposition that achieves compositional uniformity without forming inclusions or precipitates
3Manufacturing precision
If the envelope assembly is evacuated to high vacuum quality, then crystal growth quality is improved, but the presence of flow restrictors makes evacuation slow and inefficient
Solution Approach 1:
The patent implements a dynamic evacuation process using a multi-stage pumping system. Initially, rough pumping is performed with all ports open, then progressive isolation of sections allows efficient high-vacuum pumping. This dynamic approach to evacuation sequencing overcomes the flow restrictor bottleneck, achieving high vacuum quality without excessive time loss
Solution Approach 2:
The envelope assembly is segmented into multiple independently pumpable sections separated by isolation valves. This segmentation allows each section to be evacuated separately and efficiently, overcoming the flow restrictor limitation by creating multiple parallel evacuation paths, thus reducing total evacuation time while achieving high vacuum quality
4Ease of manufacture
If demountable joints with O-rings are used for assembly, then ease of assembly is improved, but vacuum leakage occurs compromising the vacuum environment
Solution Approach 1:
The patent employs flexible O-ring seals in demountable joints to create vacuum-tight connections. The O-rings deform to fill gaps and seal effectively at the demountable joints between envelope sections, source containers, and other components. This flexible sealing approach maintains vacuum tightness while enabling easy assembly and disassembly of the system
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the rapid and efficient evacuation of the system to achieve high vacuum quality, minimizing impurities and maintaining a controlled environment for crystal growth, resulting in high-quality, large-size bulk crystal materials with reduced defects.
Implementation Method 1
the source reservoir(s) are heated to produce the vapour form of their respective contents which is transported via the crossmember to the growth zone
Implementation Method 2
Vapour phase material is provided to the growth zone, causing nucleation and subsequent deposition of the material to grow the crystal
Data Source
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AI summary
An apparatus for vapour phase crystal growth is described comprising an envelope assembly having at least one source module defining at least one source volume, at least one growth module defining at least one growth volume, and at least one manifold module defining at least one manifold volume, wherein one or more source modules, a manifold module and a growth module are configured co-operably to define a fluidly continuous envelope volume including a flow restrictor between each source volume and the growth volume; a vacuum vessel containing one or more such envelope assemblies; an evacuator to evacuate the vacuum vessel; a fluid communication path between the envelope volume and the vacuum vessel associated with each source volume at a location on the source volume side of its associated flow restrictor that is configurable to be open during evacuation; and a closure mechanism configured to selectively restrict, and preferably substantially close, the fluid communication path between each source volume and the vacuum vessel after evacuation. A method of employing such an apparatus for vapour phase crystal growth, including a method of preparing such an apparatus for vapour phase crystal growth in an evacuation phase, are also described.