A polycrystalline CZT ingot for single crystal growth produced at
TuocaiTech’s facility in the heart of China’s Optics Valley ©TuocaiTech
Silicon-based semiconductors have dominated the ongoing “semiconductor war” between China and the West. However, in their recent technological tit-for-tat, global attention has been diverted to non-silicon-based or compound semiconductors, especially gallium-based ones, after the recent announcement of the new gallium export controls in China.
As articles about compound semiconductors, i.e .gallium arsenide (GaAs), gallium nitride (GaN) and indium phosphide (InP), flood newsfeeds, a less well-known compound semiconductor has quietly ignited a technological revolution, in applications from clean energy to diagnostic medicine — cadmium telluride (CdTe).
Comparing diagnostic imaging and phone technologies, the heart of our current medical imaging tools is still in the legacy analog era, while phones have become smart, so smart that artificial intelligence is now a reality. A CdTe-based semiconductor called cadmium zinc telluride (CZT) is changing the narrative, enabling the shift from scintillators to solid-state detectors used in x-ray to gamma-ray medical imaging. This room temperature semiconductor can directly convert X-ray or gamma-ray photons into electrons, resulting in better spatial resolution and sensitivity. This also means lower administered doses of radiopharmaceuticals.
CZT has been well-researched for 40 years, but its commercialisation has been impeded by challenges in single crystal growth and mass production at economic scale. Finally, in 2019, the CZT revolution began. Unfortunately, the pandemic pushed back its adoption, as hospital funding prioritised vaccines, PPE, portable x-rays and ventilators. But, inevitably, in a post-pandemic world, medical diagnostic imaging will shift to solid-state detectors – transforming conventional SPECT, CT and X-ray scans, dental imaging, mammography, etc.
The application of such CdTe-based semiconductors is not restricted only to medical imaging but covers an array of radiation detector products for x-ray and gamma-ray detection. CdTe-based technologies are now powering up airport baggage scanners, drones and ground rovers for site monitoring (radioactivity) and position sensing, and even allowing us to capture images of blackholes in our universe. Furthermore, apart from x-ray and gamma-ray detection, CdTe with mercury (Hg), creating HgCdTe (MCT) has been the primary semiconductor for infrared detection, especially in remote sensing and military technology (night vision).
In a nutshell, CdTe-based semiconductors will revolutionise anything related to x-ray, infrared and gamma ray detection. But CdTe has another application that has brewed up a separate yet tensed discussion on its criticality in clean energy technologies. With China as the leading silicon-based solar technology producer, the US is aiming massively to push its homegrown solar technology — through CdTe thin film solar photovoltaics.
High to ultra-high purity cadmium and tellurium are used to create the poly- to single crystals of CdTe-based semiconductors. Even though the applications are wide-ranging, CdTe is still considered a low-volume market compared with other compound semiconductors. And only few refiners and ultra-refiners spread across the world have the expertise and production capacity to meet the sensitive specifications for such materials.
By Dan Manaig
Director of Global Sales and Strategy
MMTA member TuocaiTech is a manufacturer of high purity metals and compounds that enable tomorrow’s technologies.
www.tuocaimetals.com
