Materials & Detectors
The cadmium telluride (CdTe) family of materials (CZT, CdMnTe etc) is universally recognised as the premier material for digital and spectral radiation detectors. However, it has historically proved very difficult to produce them in a consistent and commercially viable way.
Current manufacturers all use techniques based on liquid phase growth methods, but these suffer from poor yield of sufficiently high quality material due to fundamental limitations arising from the physical materials properties.
This has meant device and system builders have been unable to design and construct mainstream equipment around CdTe/CZT, although the materials are used in certain high end or cost insensitive applications. Many technological advances have been and will continue to be made, but the process limitations impose obstacles on scalability and materials uniformity.
Multi-Tube Physical Vapor Transport (MTPVT) Kromek produces the crystals using a novel vapour phase growth technique - MTPVT, a process that originated at Durham University, UK, as a result of 25-years of research on vapor growth techniques for bulk crystalline materials. This patented technique is capable of producing material of improved structural integrity, uniform composition and exceptional purity.
Kromek has further developed and refined the technique into a highly controllable and flexible production growth system for CdTe and CZT allowing it to develop, manufacture and integrate detectors using the CdTe family of materials.
These detectors differ significantly in their operation and output from traditional detectors, such as Si diode scintillators which indirectly generate output through use of an x-ray scintillator, and are employed as direct converters of x-ray and gamma ray photon energy into electrical signals.
Hetero-epitaxially seeded growth
Low initial growth rates allow lattice mismatch defects to be grown out and result in zero stress materials within 20 microns.
U tube configuration radiatively decouple the growth and source heaters. This allows independent control of these growth parameters during the growth process.
Controllable source flows
Use of flow orifices between sources and growth together with annular pumping at the growth side makes source flows essentially independent of growth side pressure. This decoupling allows mass flow control.
Semi-open growth for impurity removal
High volatility impurities and stoichiometry imbalances which cause diffusion limitations in closed systems are eliminated.
Multiple independent sources including dopants
Independent CdTe and ZnTe precursors allows active control of stoichiometry. Exact Cd and Te concentrations are affected by the source and growth temperatures together with the pumping annulus dimensions. Dopants can be introduced as compounded or pure materials in additional furnaces.
Bulk alloy growth
Despite initial epitaxial growth rates, bulk growth allows 30mm of useful material to be grown in a one week growth cycle time.
Optical access at the source and growth furnaces allows the use of multiple in-situ instrumentation. This includes interferometric measurement of nucleation and ramp to growth, optical absorption measurement of species concentration and pyrometric measurement of source and growth surfaces.
Boule to detectors in 3-days
Due to unique properties of material produced on MTPVT, there is no requirement for post-growth processing before detectors can be fabricated. This reduces both costs and time within detector manufacturing.